BIOLOGICAL CONTROL OF THE INVASIVE BROWN MARMORATED STINK BUG 

(HALYOMORPHA HALYS) (HEMIPTERA: PENTATOMIDAE) IN MICHIGAN BY 

INTRODUCED AND NATIVE PARASTIOIDS IN A CHANGING CLIMATE 

By  

Olivia Claire Simaz 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

A THESIS 

Submitted to 

Michigan State University 

in partial fulfillment of the requirements 

for the degree of 

Entomology – Master of Science 

2020 

i 

 

 

ABSTRACT 

 

BIOLOGICAL CONTROL OF THE INVASIVE BROWN MARMORATED STINK BUG 

(HALYOMORPHA HALYS) (HEMIPTERA: PENTATOMIDAE) IN MICHIGAN BY 

INTRODUCED AND NATIVE PARASTIOIDS IN A CHANGING CLIMATE 

By 

Olivia Claire Simaz 

This thesis focuses on evaluating the potential of native natural enemies and an exotic 

parasitoid to provide biological control of an invasive pest, the brown marmorated stink bug 

(Halyomorpha halys Stål) in Michigan and explores the consequences climate change might 

have both on the pest and its natural enemies.  

The first chapter provides background on the invasion of H. halys and reviews research 

on the native parasitoid community and their potential to provide biological control for this pest. 

The second chapter focuses on augmentative releases of the biological control agent, 

Trissolcus japonicus (Ashmead), which is an exotic parasitoid, discovered in Michigan in 2018. 

The importance of release size and of release frequency were tested during two years of 

augmentative releases and the native parasitoid community was surveyed. Overwintering success 

and reproduction of Tr. japonicus were confirmed but population growth was found slow. 

Parasitism by native parasitoids was below 5%, which is too low to provide control of H. halys. 

In the third chapter the effects of heat waves were evaluated on H. halys and Tr. 

japonicus. Eggs of H. halys were found to be more sensitive to heat waves than larval stages of 

Tr. japonicus. While heat waves did not reduce parasitism rates, Tr. japonicus adult mortality 

increased and their development was delayed with intensifying heat waves. These results suggest 

that Tr. japonicus could maintain its biocontrol potential even in the face of climate change. 

 

 

 

ii 

     ACKNOWLEDGEMENTS 

 

First, I would like to thank my major professor, Marianna Szűcs, for inviting me to join 

the Biological Control lab as her first graduate student. I am very grateful to have had such 

wonderful mentor for these years for professional success as well as personal growth. Thank you 

for pushing me to do better than my best. Thank you as well to the other members of my 

committee, Dr. Matthew Grieshop and Dr. Nikki Rothwell, for lending advice and expertise to 

my research.  

Thank you to the rest of the Biological Control lab, past and present, for their support and 

help throughout the past two years: B. Jarrett, C. Hernandez, B. Alred, B. Foster, S. Linder. 

Thank you to all of the technicians, J. Okuniewicz, N. Tabara, A. Jain, and M. Hamlyn involved 

in colony maintenance and field site setup. Thank you to those that helped me find field sites, 

introduced me to the growers and supplied stink bug eggs for rearing and monitoring: J. Wilson, 

L. Gut, and J. Pote. 

Thank you to the New Jersey Department of Agriculture Phillip Alampi Beneficial Insect 

Laboratory rearing facility for supplying additional H. halys eggs for our colony and Elijah 

Talamas from the Florida Department of Agriculture for parasitoid identification. Thank you to 

the following for funding: Michigan State University AgBioResearch Project GREEEN, the 

Michigan Apple Committee, Michigan State Horticultural Society, Michigan Vegetable Council 

and Nestlé Gerber.

 

iii 

TABLE OF CONTENTS 

 

LIST OF TABLES..…………………………………………………………………………...….v 

LIST OF FIGURES……...……………………………………………………………………….vi 

CHAPTER 1: The status of Halyomorpha halys invasion and its biological control in the U.S… 1 
 
Background………………………………………..………………………………………1 
 
CHAPTER 2: Augmentative field releases of the exotic parasitoid Trissolcus japonicus and 
survey of native parasitoids attacking brown marmorated sting bug ……………………………. 5 
Introduction ……………………………………………………………………………….5 
Materials and Methods…………………………………………………………………….9 
Results……………………………………………………………………………………19 
Discussion………………………………………………………………………………..27 
 

CHAPTER 3: The effects of heat waves on Halyomorpha halys survival and parasitism success 
by Trissolcus japonicus ………………………………………………………………………… 32 
Introduction………………………………………………………………………………32 
Materials and Methods………………………………………………………………...…35 
Results………………………………………………………………………………...….42 
Discussion…………………………………………………………………………….….51 

 
REFERENCES…………………………………………….…………………………………….56 

 

 

 

 

 

 

 

 

iv 

 

 

 

LIST OF TABLES 

 

Table. 2.1. Study sites, experimental design and site characteristics. All sites designated as 
‘Mixed’ had both a diversity of fruits and vegetables grown. Sites characterized as ‘Low input’ 
use a mix of conventional and organic management methods.…………………………………. 13 

Table. 2.2. Outcome of monitoring using H. halys and P. maculiventris sentinel egg masses 
deployed at 12 field sites each in 2019 and 2020.……………………………………………….20 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

v 

LIST OF FIGURES 

 

Figure.1.1. The distribution on H. halys in Michigan. Misin.msu.edu. Accessed Oct 2020…2 

 

Figure. 2.1 Study sites for Tr. japonicus releases in 2019 (solid fill) and in 2020 (pattern fill) in 
lower Michigan. Different shaded circles indicate the 4 regional blocks each year within which 
sites were assigned to different Tr. japonicus release treatments. In 2019, sites received either 0 
(control), 100 or 900 adult parasitoids as part of a single release. In 2020, sites received either 0 
(control) or 500 in a single release or 250 individuals first and then an additional 50 at a second 
release date. The four underlined release numbers indicate the sites where Tr. japonicus was 
recaptured in 2020. For exact coordinates see Table. 2.1.………...……………………………..16 

Figure. 2.2. Figure. 2.2. Total number of parasitoids of five species (or genera) emerging from 
H. halys sentinel eggs. The year of sampling is shown at the top of the graph. Parasitoids were 
released and monitored using sentinel eggs in southwestern Michigan in 2019 (left panel) and in 
southeastern Michigan in 2020 (right panel). There was no difference in the mean number of 
parasitoids emerging between months (p = 0.5342) or for the different parasitoid species (p = 
0.4565) in 2019. Note that releases and sampling took place later in 2020 than in 2019 and only 
frozen eggs were used in 2020 for monitoring, which may explain the relatively lower parasitoid 
captures……………………………….………………………………………………………….22 

 

Figure. 2.3. Mean (± SE) number of parasitoids emerging from frozen or fresh H. halys sentinel 
eggs deployed in 2019. Across species more parasitoids emerged from frozen than from fresh 
sentinel eggs (p = 0.0281) but within parasitoid species there was no difference between numbers 
emerging from frozen versus fresh eggs..……..…………………………………………………23 

 

Figure. 2.4. The relationship between the number of H. halys sentinel egg masses parasitized 
and the number of H. halys captured by pyramid traps at the 12 study sites in 2019 (R2 = 0.61). 
Dotted lines represent 95% confidence interval curves……….…………………………………24 
Figure. 2.5. Parasitoid captures by yellow sticky traps in 2020 at 12 study sites where Tr. 
japonicus was released in 2019 (left panel) and 12 sites where released in 2020 (right panel). 
Traps were changed every 3 weeks at the 2019 release sites and every 2 weeks at the 2020 
release sites. To display monthly total captures the number of parasitoids captured by each trap 
was divided in proportion of the number of days spent in the field for and given month.………25 

 

Figure. 2.6. Figure. 2.6. Mean number of H. halys captured by pyramid traps at sites where Tr. 
japonicus was released either in 2019 or 2020. The 2019 release sites were sampled both in 2019 
and 2020 (2019 West and 2020 West). The 2020 release sites were sampled in 2020 (2020 East). 
For the 2019 release sites more H. halys was captured in 2020 than in 2019 between June and 
August. Here mean captures are shown for the entire sampling season, which ended in early 
September in 2019 but continued until the end of September in 2020…………………......……26 

Figure. 3.1. Results of Experiment 1. Emergence success of H. halys nymphs from eggs exposed 
to an ambient temperature (25˚C) or four heat wave treatments (36, 38, 40, and 42˚C) in two 

 

vi 

independent trials (A: trial 1, B: trial 2). The curve is the logistic regression curve that indicates 
the probability of successful emergence at the different temperature treatments. Dots are 
randomly jittered in a vertical position. Blue dots under the curve indicate replicated egg masses, 
each with 28 eggs, from which at least one nymph emerged. Red dots above the curve are 
replications without any adult emergence. The reference categories on the right y axis show the 
probability of successful (1) or unsuccessful emergence (0) across all temperature 
treatments………………………………………………………………………………………...43 

Figure. 3.2. Results of Experiment 1. Mean (± SE) H. halys nymphs emerging from egg masses, 
each with 28 eggs, that were exposed to an ambient temperature (25˚C) or four heat wave 
treatments (36, 38, 40, and 42˚C) in two independent trials (Blue: trial 1, Red: trial 2). Letters 
indicate significant difference between temperatures within each trial……….…………………44 

Figure. 3.3. Results of Experiment 2. Emergence success of Tr. japonicus from H. halys eggs 
that were parasitized prior to exposure to an ambient temperature (25˚C) or four heat wave 
treatments (36, 38, 40, and 42˚C) in two independent trials (A: trial 1, B: trial 2). The curve is the 
logistic regression curve that indicates the probability of successful emergence at the different 
temperature treatments. Dots are randomly jittered in a vertical position. Blue dots under the 
curve indicate replicated H. halys egg masses, each with 28 eggs, from which at least one adult 
Tr. japonicus emerged. Red dots above the curve are replications without any adult emergence. 
The reference categories on the right y axis show the probability of successful (1) or 
unsuccessful emergence (0) across all temperature treatments…………………………...……..45 

Figure. 3.4. Results of Experiment 2. Mean (± SE) number of Tr. japonicus adults emerging 
from H. halys egg masses, each with 28 eggs, that were parasitized prior to exposure to an 
ambient temperature (25˚C) or four heat wave treatments (36, 38, 40, and 42˚C) in two 
independent trials (A: trial 1, B: trial 2). Letters indicate significant difference between 
temperatures within each trial……………………………………………………........................46 

Figure. 3.5. Results of Experiment 2 trial 1. Mean (± SE) development time (days) of Tr. 
japonicus exposed to an ambient temperature (25˚C) or four heat wave treatments (36, 38, 40, 
and 42˚C). Note that development time here is shown as the time between the first day of heat 
wave treatments and the first adult emergence. Eggs were parasitized five days prior to the start 
of the experiment. Letters indicate significant difference between temperatures.……….……...46 

Figure. 3.6. Results of Experiment 3. Emergence success of Tr. japonicus from H. halys eggs 
that were parasitized during exposure to an ambient temperature (25˚C) or four heat wave 
treatments (36, 38, 40, and 42˚C). The curve is the logistic regression curve that indicates the 
probability of successful emergence at the different temperature treatments. Dots are randomly 
jittered in a vertical position. Blue dots under the curve indicate replicated H. halys egg masses, 
each with 28 eggs, from which at least one adult Tr. japonicus emerged. Red dots above the 
curve are replications without any adult emergence. The reference categories on the right y axis 
show the probability of successful (1) or unsuccessful emergence (0) across all treatments……48 

Figure. 3.7. Results of Experiment 3. Mean (± SE) number of Tr. japonicus adults emerging 
from H. halys egg masses, each with 28 eggs, that were parasitized during exposure to an 
ambient temperature (25˚C) or four heat wave treatments (36, 38, 40, and 42˚C). Letters indicate 
significant difference between temperatures…………………………………………………….48 

 

vii 

Figure. 3.8. Results of Experiment 3. Mean (± SE) development time (days) of Tr. japonicus 
exposed to an ambient temperature (25˚C) or four heat wave treatments (36, 38, 40, and 42˚C) in 
the first experiment. Eggs were parasitized during the heat wave treatments. Letters indicate 
significant difference between temperatures.………….……………………………………..….49 

Figure. 3.9. Survival of adult Tr. japonicus when exposed to an ambient temperature (25˚C) or 
four heat wave treatments (36, 38, 40, and 42˚C) for five days. The curve is the logistic 
regression curve that indicates the probability of successful emergence at the different 
temperature treatments. Dots are randomly jittered in a vertical position. Blue dots under the 
curve indicate females that survived and red dots above the curve indicate females that died by 
day five. The reference categories on the right y axis show the probability of successful (1) or 
unsuccessful emergence (0) across all temperature treatments…………………………………49 

Figure. 3.10. Results of Experiments 4 and 5 testing transgenerational effects Second generation 
(F2) emergence rates of Tr. japonicus where the maternal generation (F1) was exposed either as 
5-10 days (A – Experiment 4) or 1-4 days old (B – Experiment 5) larvae to an ambient 
temperature (25˚C) or four heat wave treatments (36, 38, 40, and 42˚C). Blue dots indicate 
replicated H. halys egg masses, each with 28 eggs, from which at least one adult emerged. Red 
dots are replications without any adult emergence.………………………..…………………….50 

Figure. 3.11. Results of Experiments 4 and 5 testing transgenerational effects. Mean (± SE) 
number of second-generation (F2) Tr. japonicus adults emerging from mothers that were 
exposed either as 5-10 days (Experiment 4 - Blue) or 1-5 days (Experiment 5 - Red) old larvae to 
an ambient temperature (25˚C) or four heat wave treatments (36, 38, 40, and 42˚C). Letters 
indicate significant difference between temperatures within each experiment. Numbers above 
bars show the number of replications. ………………………………………………………..…5

 

viii 

CHAPTER 1: The status of Halyomorpha halys invasion and its biological control in the 

U.S. 

Background 

Brown marmorated stink bug, Halyomorpha halys Stål (Hemiptera: Pentatomidae) is a 

severe agricultural pest in Eastern and Mid-Atlantic states and is an emerging pest in Michigan, 

threatening fruit and vegetable production. Native to East Asia, H. halys was first detected in the 

US in the late 1990s and since has established in 44 states and four Canadian provinces 

(Hoebeke and Carter, 2003; stopbmsb.org). It was discovered in Michigan in 2010 and has since 

spread to all but four counties (Figure. 1.1) (Wilson et al. 2018; www.misin.msu.edu). H. halys is 

extremely polyphagous, being able to feed on over 200 different plant species including tree 

fruits, vegetables, field crops, ornamentals, and native vegetation (Leskey et al., 2012a). 

Economic losses attributed to H. halys feeding were first recorded in 2006 in Mid-Atlantic 

orchards and by 2009, H. halys damage on apples was estimated to cost $37 million (Leskey et 

al. 2012b). Given that Michigan is the third largest producer of apples in the USA, H. halys is 

poised to become a major threat to the Michigan apple industry (MI Agricultural Statistics 2017-

2018). In addition to becoming a crop pest, H. halys is also a nuisance pest due to its habit of 

overwintering in human-made structures, and in some instances, people can find tens of 

thousands of stink bugs in their homes during the fall (Leskey et al., 2012).

 

1 

Figure.1.1. The distribution on H. halys in Michigan. Misin.msu.edu accessed Oct 2020. 

 

 

Management of H. halys currently relies on the use of broad-spectrum pesticides applied 

throughout the growing season (Leskey et al. 2012b). The increase in the amount and frequency 

of pesticide applications for H. halys management has interfered with integrated pest 

management (IPM) programs by indiscriminately killing natural enemies and resulted in 

outbreaks of secondary pests that were previously successfully kept at bay by biological control 

(Leskey et al. 2012a; Rice et al. 2014). Despite continued chemical control within cropping areas 

large populations persist in natural areas and other plant hosts where they can recolonize 

cropping system. Thus, alternative control methods that include biological control by either 

native or introduced natural enemies are likely to be essential for managing this pest in the long 

term.  

Surveys of natural enemies covering mostly Eastern and Central states in the U.S. found 

that at least eight native endoparasitoids from three families (Scelionidae, Eupelmidae, and 

 

2 

Encyrtidae) and four genera (Telenomus, Trissolcus, Anastatus and Ooencyrtus) already attack 

H. halys eggs in the field (reviewed in Abram et al. 2017). The ability of different parasitoid 

species to develop on this new host varies among crops and regions (Abram et al. 2017; 

Cornelius et al. 2016a; Cornelius et al. 2016b; Dieckhoff et al. 2017; Jones et al. 2017; Ogburn et 

al. 2016). To date, rates of native parasitoid emergence from viable H. halys eggs are generally 

low, below 5% in most cases, and vary among environments between 0 – 59% (Abram et al. 

2017; Dieckhoff et al. 2017). A 9-year survey in Delaware found no indication that parasitism by 

native parasitoids increased over time (Dieckhoff et al. 2017). These data indicate that native 

parasitoids alone may not provide effective biological control of H. halys in the near future. 

Classical biological control, the introduction of host-specific natural enemies from the 

native range of exotic species is a critical component of sound long-term management of many 

invasive species. The exotic egg parasitoid, Trissolcus japonicus Ashmead (Samurai wasp) 

(Hymenoptera: Scelionidae) originating from Eastern Asia, the native range of H. halys, has been 

under investigation as a candidate for a classical biological control program since 2007 (Talamas 

et al. 2015). Adult female wasps lay their eggs into H. halys eggs and their larvae consume the 

entire stink bug embryo. Tr. japonicus has shown great potential to be a successful biological 

control agent because it can parasitize 50-70% of H. halys eggs (Yang et al. 2009; Talamas et al. 

2013). However, studies in quarantine revealed that Tr. japonicus can attack and develop on at 

least seven native stink bug species in Oregon (Hedstrom et al. 2017) and 15 native species in 

Michigan (Botch and Delfosse, 2018). Because Tr. japonicus attacks native stink bugs it has not 

been field released.  

Even though field release is not permitted adventive (accidentally introduced) 

populations of Tr. japonicus were found first in MD in 2014 and, within a few years, in some 

 

3 

Mid-Atlantic and Western states (Talamas et al. 2015; Hedstrom et al. 2017; Herlihy et al. 2016; 

Milnes et al. 2016; stopbmsb.org). Molecular analyses confirmed that the adventive populations 

are genetically distinct from those in quarantine, indicating these were unrelated and independent 

introductions rather than accidental escapees from quarantine colonies (Milnes et al. 2016). 

Given its effectiveness on H. halys in Asia, the accidental introduction and spread of Tr. 

japonicus in the U.S., we need to further examine its potential as an effective agent of natural H. 

halys population suppression.  

Despite the presence of Tr. japonicus in the field in several states, interstate redistribution 

of this parasitoid is not permitted. However, biological control programs can be initiated within 

states where Tr. japonicus has been detected using the captured individuals for rearing. The mass 

rearing and redistribution of Tr. japonicus is already underway in several Eastern and Western 

states to augment populations (BMSB SCRI Annual Report, 2018). Tr. japonicus arrived at 

neighboring Ohio in 2017 (stopbmsb.org) and was first found in Michigan in 2018 at a single 

location despite widespread sampling within the state (Jarrett et al. 2019). Given the pattern of 

detection across the U.S., Tr. japonicus appears to be expanding its populations westward from 

an initial introduction point on the east coast and was found in Michigan very early upon its 

arrival. Thus, its density was likely very low around 2018, and its state-wide distribution very 

limited. The second chapter of this thesis focuses on augmentative releases of Tr. japonicus 

using a laboratory rearing that had been initiated from live field captures in Michigan.  

 

 

 

 

4 

CHAPTER 2: Augmentative field releases of the exotic parasitoid Trissolcus japonicus and 

survey of native parasitoids attacking brown marmorated sting bug 

 

Introduction 

 

Classical biological control has a long history, with introductions of biological control 

agents dating back to the 1880s (Cock et al. 2016), but we still know relatively little about how 

to release biological control agents against invasive insects to ensure their establishment. Less 

than 33% of predator and parasitoid introductions against insect pests led to establishment 

worldwide (Cock et al. 2016), while in North America, an estimated 54% of released parasitoid 

species have established since 1985 (Driesche et al. 2020). Multiple mechanisms may influence 

establishment, including abiotic conditions, species-specific biological traits, stochastic 

processes, Allee effects, or the level of genetic variation within the released population. 

However, the most consistent predictor of establishment success across a wide range of species 

is found to be propagule pressure: the combined size and number of introductions (Blackburn et 

al. 2015; Lockwood et al. 2005; Simberloff 2009). Recent experimental laboratory studies using 

insects also confirm that higher release sizes increase establishment success (Hufbauer et al. 

2013; Szűcs et al. 2014; Szűcs et al. 2017). This could be due to multiple factors including a 

reduction in Allee effects, demographic, and environmental stochasticity at larger release sizes 

(Boyce et al. 2006; Lande, 1993). Additionally, more individuals in a founding group usually 

harbor higher genetic diversity, which could reduce the probability of inbreeding, increasing 

chances of adaptation to novel environmental conditions and ensuring longer-term persistence of 

populations (Drake, 2006; Forsman, 2014; Rius and Darling, 2014).  

 

5 

 

For insect biological control, Hopper and Roush (1993) reviewed releases against species 

within the order Lepidoptera and found indirect evidence that release size was positively 

correlated with establishment success of natural enemies (Hopper and Roush, 1993). However, 

the three field studies, that we know of, that experimentally manipulated release size of 

parasitoid classical biological control agents did not find the same relationship (Borowiec et al. 

2018; Fauvergue and Hopper 2009; Fauvergue et al. 2007). Establishment rates were similar for 

Neodryinus typhlocybae (Ashmead) (Hymenoptera: Dryinidae) against plant hoppers regardless 

of release sizes (1, 10 or 100 females) (Fauvergue et al. 2007). The release of 1,200 or 11,400 

aphid mummies parasitized with Aphelinus asychis Walker (Hymenoptera: Aphelinidae) also 

yielded similar parasitoid establishment success (Fauvergue and Hopper, 2009). Neither release 

size nor release frequency explained establishment success of Torymus sinensis Kamijo 

(Hymenoptera: Torymidae) against the chestnut gall wasp (Borowiec et al. 2018). In weed 

biological control, experimental field introductions have shown that larger releases of biological 

control agents are more likely to establish and persist (Grevstad, 1999a; Grevstad, 2006; 

Memmott et al. 2005; Memmott et al. 1998). However, there are examples of a single female 

founding populations (Grevstad, 1999a) and of releases made with 65,000 individuals failing 

(Grevstad et al. 2011).  

 

Establishment success may be impacted not only by the number of individuals in a single 

release (propagule size) but also by the frequency of releases (propagule number). Models 

considering propagule number provide contrasting recommendations for biological control 

release strategies. Grevstad (1999b) recommends several smaller introductions to a variable 

environment and a single large release when Allee effects are present in a homogenous 

environment. In contrast, if the hosts are established only at a few sites, a few large releases were 

 

6 

predicted to yield success (Shea and Possingham, 2000). For parasitoid releases, Hopper and 

Roush (1993) recommended releasing over 1000 individuals at a single site and time. If the 

number of individuals available for releases is limited, single larger releases were predicted to 

maximize establishment, but if environmental stochasticity is substantial, then several smaller 

releases spread over time may be the optimal approach (Hopper and Roush, 1993).  

 

Given the scarcity of experimental field studies and the contrasting recommendations of 

models and laboratory experiments, there are no specific guiding principles on how to release 

parasitoid biological control agents. The lack of information on release strategies can be 

particularly problematic for biocontrol agents that are difficult or expensive to rear in large 

numbers, and haphazard releases can lead to the loss of significant time and financial 

investments in case they do not establish. New releases of classical biological control agents that 

are imported from the native range of a pest would be ideal to assess experimentally how best to 

release parasitoids. However, there has been a steep decline in exotic parasitoid approvals and 

releases in the past few years (Driesche et al. 2020), and thus few opportunities for such studies. 

Nevertheless, exotic parasitoids sometimes follow invasive pests and their redistribution could 

provide insights into the effectiveness of different release strategies for establishment.  

 

Trissolcus japonicus (Ashmead) (Hymenoptera: Scelionidae) is an exotic egg parasitoid 

that was introduced accidentally, likely along with its host, the brown marmorated stink bug 

(Halyomorpha halys (Stål)) (Hemiptera: Pentatomidae) from eastern Asia. Halyomorpha halys 

was found in the US in 1996, while adventive populations of Tr. japonicus were first discovered 

in 2014 in Maryland and in subsequent years in multiple mid-Atlantic and Western states 

(Hedstrom et al. 2017; Herlihy et al. 2016; Hoebeke and Carter, 2003; Milnes et al. 2016; 

Northeastern IPM Center, 2020; Talamas et al. 2015). Since its introduction, H. halys has spread 

 

7 

across 44 states and four Canadian provinces and has become a primary agricultural pest of 

multiple fruit and vegetable crops (Abram et al. 2019, Gariepy and Talamas, 2019; Leskey and 

Nielsen, 2018; Northeastern IPM Center, 2020). A suite of native parasitoids from three families 

(Scelionidae, Eupelmidae, and Encyrtidae) and four genera (Telenomus, Trissolcus, Anastatus 

and Ooencyrtus) were found to attack H. halys eggs in North America, but their rates of 

parasitism had been too low (<10%) to provide control (reviewed in Abram et al. 2017). 

Trissolcus japonicus has been the primary candidate for a classical biological program (Talamas 

et al. 2015), because it can parasitize 50–80% of H. halys eggs in its native range (Yang et al. 

2009; Zhang et al. 2017). Host-specificity tests have shown that it can attack over 10 native stink 

bug species but strongly prefers H. halys both in the laboratory and in the field (Botch and 

Delfosse, 2018; Hedstrom et al. 2017; Milnes and Beers, 2019). Thus, once it fortuitously 

arrived, multiple states started conducting augmentative releases to increase its geographic 

distribution and population densities to accelerate biological control (Jentsch 2017; Milnes and 

Beers, 2019).   

 

In Michigan, Tr. japonicus was first found in 2018 at a single location despite extensive 

sampling across the state (Jarrett et al. 2019). The rate of discovery within the U. S. suggests that 

it has spread from the east coast to the Midwest and that it was discovered in Michigan soon after 

its arrival from neighboring Ohio, where it had been found just a year before, in 2017. A colony 

of Tr. japonicus was built from this initial capture and augmentative releases were conducted in 

2019 and 2020 across the state, testing the importance of release size in year one, and of release 

frequency in year two for establishment. Fresh or frozen H. halys sentinel eggs and yellow sticky 

cards placed at two different heights were used to monitor the presence of Tr. japonicus before 

and after releases and the diversity of native parasitoids attacking H. halys in Michigan. In 

 

8 

addition, potential non-target effects of Tr. japonicus were evaluated on a native beneficial stink 

bug species, Podisus maculiventris (Say) (Hemiptera: Pentatomidae).  

 

The overall objective of the study was to increase the geographic distribution and 

population densities of Tr. japonicus across Michigan to accelerate biological control of H. 

halys. The hypotheses were that larger releases in 2019 and multiple releases in 2020 would 

establish at higher rates than smaller or single releases, respectively. In addition, the expectation 

was that there would not be a difference in parasitism between fresh and frozen H. halys sentinel 

eggs (Abram et al. 2017) and that eggs and traps placed higher in the canopy would capture more 

parasitoids than those closer to the ground (Quinn et al. 2019).   

 

Materials and Methods 

Insect rearing 

 

The colony of Tr. japonicus was started from five individuals, two males and three 

females that emerged from a single H. halys sentinel egg mass placed at the Student Organic 

Farm at Michigan State University (MSU) campus (42.6749, -84.4897) in August 2018 (Jarrett et 

al. 2019). Wasps were reared by providing either fresh (< 72 h old) or frozen (at -80˚C) H. halys 

egg masses to groups of 5–15 mixed sex individuals for 3–7 days for oviposition in 10-dram 

vials. A drop of honey was placed on the lids to provision wasps. Vials were kept in an incubator 

at 20˚C and 70% humidity with a photoperiod of 16:8 L:D. Adult wasps emerged 14–21 days 

following oviposition.  

 

Halyomorpha halys eggs used for rearing Tr. japonicus originated either from colonies 

maintained on MSU campus or from the New Jersey Department of Agriculture Phillip Alampi 

 

9 

Beneficial Insect Laboratory rearing facility. Adult H. halys was reared in mesh cages (30 x 30 x 

60 cm) (Educational Science, League City, TX, U.S.) by keeping 40-60 mixed-sex adults in each 

cage at 25°C, 50–75% humidity and 16:8 L:D photoperiod in a climate controlled room. Nymphs 

were housed in 236 ml clear plastic containers (Ziploc® large rectangle). A six square cm hole 

was cut on the lids and covered with gauze to provide ventilation. All stages were provided water 

via dental wicks (Dynarex N/S #2 Medium) inserted into 60 ml cups (Gordon Food Service) 

filled with water. Their diet included organic green beans, snap peas, broccoli, carrots, apples, 

and mixed nuts. The native stink bug, P. maculiventris, used to assess non-target effects of Tr. 

japonicus, was reared in groups of 40–50 in 1.2 L clear, round plastic containers (Gordon Food 

Service) at 25˚C, 50–75% humidity and 16:8 L:D photoperiod in a climate chamber. Water was 

provided via dental wicks inserted in 60 ml cups filled with water. Their diet included wax 

worms (Top Hat Cricket Farm Inc., Portage, Michigan) and organic green beans. For both stink 

bug colonies, eggs were collected two to three times weekly and used either to rear parasitoids, 

as sentinel eggs in the field, returned to the colony, or were frozen at -80˚C for later use. 

 

Experimental design 

 

To test how different release methods may impact establishment success of Tr. japonicus, 

a 2-year field study was conducted. In year one, in 2019, the importance of release size was 

evaluated. For this study 12 field sites were chosen in southwestern and central Michigan (Table 

2.1, Figure. 2.1). A randomized complete block design was used with three release treatments (0, 

100, or 900 individuals) assigned randomly within each block, replicated over four blocks. The 

blocks represented sites that were in geographic proximity (Figure. 2.1). Releases took place in 

2019 and were monitored in 2019 and in 2020. Establishment success of the different release 

 

10 

treatments was evaluated using a mix of fresh and frozen H. halys sentinel eggs in 2019 (Table 

2.2) and yellow sticky traps (Trécé® AM no-Bait traps) in 2020 to capture Tr. japonicus. Half of 

the sentinel eggs and the yellow sticky traps were placed at 1.5 m and the other half at 3.5 m 

height to evaluate parasitoid activity at different heights. The density of H. halys was measured 

using four pyramid traps at each of the 12 study sites both in 2019 and 2020. Non-target effects 

of Tr. japonicus on native stink bugs were evaluated by placing P. maculiventris sentinel eggs in 

2019 at sites where 900 Tr. japonicus had been released, where the potential for attack was 

highest. Parasitism by native species was evaluated by identifying parasitoids emerging from H. 

halys sentinel eggs in 2019.  

 

To test how the release frequency may impact establishment success, 12 new study sites 

were identified in southeastern Michigan in 2020 (Table 2.1). A randomized complete block 

design was used with three release treatments: 0 (control), 500 wasps released at one date, or 250 

wasps at one date and 50 more wasps four weeks later. Release treatments were replicated over 

four sites in four blocks that were assigned based on geographic proximity (Figure. 2.1). 

Establishment success was evaluated by monitoring Tr. japonicus numbers with frozen H. halys 

sentinel eggs and with yellow sticky traps in 2020. Half of the sentinel eggs and the yellow 

sticky traps were placed at 1.5 m and the other half at 3.5 m height to evaluate parasitoid activity 

at different heights. The density of H. halys was measured using four pyramid traps at each of 

the 12 study sites. 

 

 

 

 

11 

Experimental procedures 

 

The main criterion for choosing sites was to have relatively high densities of H. halys in 

the region as assessed by a multi-year monitoring effort prior to this study. Another criterion was 

to have at least one side of the field bordered with a woodlot that can provide habitat for H. halys 

and Tr. japonicus and where pesticide drift would be minimized. Most study sites were apple 

orchards (n = 16) managed either conventionally (n = 14) or using low input or organic methods 

(n = 2). Eight sites had a mix of crops of both different fruits and vegetables and were either 

managed conventionally (n = 1) or with low input or organic means (n = 7) (Table 2.1).    

 

Adult wasps were released in both years within the wood lots, at least 10 m from the field 

edges using 500 ml plastic deli cups (Gordon Food Service) with the lids removed, raised into 

the canopy on a 3 m long pole. Releases were aimed to coincide with peak H. halys oviposition 

that is estimated to occur between 460 and 734 growing degree days (base 14.17˚C starting with 

January 1), based on estimates modeled for Geneva, New York by Nielson et al. (2016). These 

degree days corresponded to June 9–27 in 2019 and June 9–25 in 2020 in East Lansing, 

Michigan. Single releases took place on June 22 or at 521 degree days in 2019 

(enviroweather.msu.edu). For the 2020 field season the first releases (n = 250 or 500) took place 

on July 1 or at 873 degree days and the second releases (50 individuals added to the 250 prior 

release) took place on Aug 4 or at 1674 degree days.  

 

 

 

12 

Table. 2.1. Study sites, experimental design and site characteristics. All sites designated as ‘Mixed’ had both a 

diversity of fruits and vegetables grown. Sites characterized as ‘Low input’ use a mix of conventional and organic 

management methods. 

Block 

Release 
size 

Release 
date 

City 

Bath 

Charlotte 

St. Johns 

Conklin 

Grand Rapids 

Sparta 

Grand Junction 

Covert 

Bangor 

Benton Harbor 

Coloma 

Hartford 

Burton 

Davison 

Flint 

Washington 

Washington 

Armada 

Britton 

Milan 

Chelsea 

Linden 

Fenton 

Howell 

 

1 

1 

1 

2 

2 

2 

3 

3 

3 

4 

4 

4 

5 

5 

5 

6 

6 

6 

7 

7 

7 

8 

8 

8 

0 

100 

900 

0 

100 

900 

0 

100 

900 

0 

100 

900 

0 

2019 

2019 

2019 

2019 

2019 

2019 

2019 

2019 

2019 

2019 

2019 

2019 

2020 

Latitude  Longitude  Crop 

Management 

42.8566 

-84.4083  Mixed 

Low input 

42.6337 

-84.7877  Mixed 

Organic 

43.1207 

-84.6252 

Apple 

Conventional 

43.1526 

-85.8195 

Apple 

Conventional 

43.0629 

-85.7396 

Apple 

Conventional 

43.1113 

-85.7580 

Apple 

Conventional 

42.3450 

-86.0502 

Apple 

Conventional 

42.3066 

-86.2537 

Apple 

Conventional 

42.2949 

-86.1816 

Apple 

Conventional 

42.0829 

-86.3521  Mixed 

Conventional 

42.1615 

-86.3123  Mixed 

Low input 

42.1852 

-86.1749 

Apple 

Conventional 

43.0256 

-83.5747 

Apple 

Low input 

Low input 

250+50 

2020 

42.9692 

-83.4894 

Apple 

500 

0 

2020 

2020 

43.0321 

-83.6785 

Apple 

Organic 

42.8003 

-83.0698 

Apple 

Conventional 

250+50 

2020 

42.7866 

-83.0215 

Apple 

Conventional 

500 

0 

2020 

2020 

42.8608 

-82.9493 

Apple 

Conventional 

42.1425 

-83.6286  Mixed 

Conventional 

250+50 

2020 

41.9598 

-83.9226  Mixed 

Conventional 

500 

0 

2020 

2020 

42.2579 

-84.1103  Mixed 

Organic 

42.6898 

-83.8726 

Apple 

Abandoned 

250+50 

2020 

42.6919 

-83.7498 

Apple 

Conventional 

500 

2020 

42.8059 

-83.7945 

Apple 

Conventional 

Halyomorpha halys sentinel eggs 

 

Halyomorpha halys sentinel eggs were used to monitor the presence of Tr. japonicus and 

of native parasitoids during the season when parasitoids were released; in 2019 at the 

southwestern release sites and in 2020 at the southeastern release sites. Sentinel eggs were not 

used at the 2019 release sites to monitor in 2020, only yellow sticky traps. In 2019, a mix of 

 

13 

fresh (< 72 h old) and frozen eggs were used, while in 2020 only frozen eggs were used (Table 

2.2). Ten H. halys sentinel egg masses were deployed bi-weekly between May 24 and Sept 9 in 

2019 for a total of 840. Half of the egg masses were glued (Elmer’s® extra strength non-toxic) to 

leaves of the surrounding vegetation at 1.5 m height and half were glued to leaves that were 

raised to 3.5 m height on bamboo poles to test how height may influence parasitism rates (Quinn 

et al. 2019). Eggs were left in the field for 48 hours then brought back to the lab and incubated at 

20˚C, 50–75% humidity and 16:8 L:D photoperiod in a climate chamber. Eggs were monitored 

for parasitoid emergence for 2 months. At the 12 field sites where wasp releases took place in 

2020, monitoring proceeded in a similar manner as described for the 2019 releases by placing 10 

H. halys sentinel egg masses at each of the 12 field sites bi-weekly between July 2 and Sept 15 

for a total of 430.  

 

Podisus maculiventris sentinel eggs 

 

Potential non-target effects of Tr. japonicus were monitored in 2019 by placing at least 5 

fresh P. maculiventris egg masses, depending on availability, at 3.5 m height biweekly at sites 

that received 900 wasps. Podisus maculiventris egg masses were placed on the same leaves as 

the H. halys sentinel eggs to provide a direct choice for oviposition to parasitoids. In 2019, 285 

P. maculiventris egg masses were deployed between July 2 and Sept 3. No P. maculiventris eggs 

were deployed in 2020.   

 

 

 

 

14 

Yellow sticky traps 

 

Yellow sticky traps were used for monitoring Tr. japonicus and native parasitoids in 2020 

both at the 2019 and 2020 release sites. At the 2019 release sites, eight traps were placed every 

three weeks between June 11 and Sept 4 with four at 1.5 m and four at 3.5 m height for a total of 

384. At the 2020 release sites, 8 traps were placed at each site biweekly, at the same time when 

H. halys sentinel eggs were retrieved, between June 13 and Sept 15 for a total of 400 across the 

12 sites. At a few monitoring dates certain sites could not be accessed because of pesticide 

applications in the orchards and thus data are missing for sentinel eggs and yellow sticky traps. 

 

 

Pyramid traps 

 

The density of H. halys was monitored using pyramid traps in 2019 at the 12 release sites, 

and in 2020 at 24 sites to include all sites where Tr. japonicus releases had taken place in the two 

years combined. At each study site, four pyramid traps were placed 7 m apart in the woodlot 

where releases had taken place. Each trap was baited with a dual stink bug lure (Trécé 

Pherocon® Dual Lure). The cone at the top of the traps was lined on the inside with a piece of 

mesh infused with deltamethrin (D-Terrence® net, Vestergaard S.A., Lausanne, Switzerland) to 

kill any stink bugs captured. At the 2019 release sites traps were checked biweekly between May 

24 and Sept 9 in 2019, and every three weeks between June 25 and Oct 7 in 2020. At the 2020 

release sites, traps were checked biweekly between July 1 and Oct 9 in 2020.  

 

15 

Figure. 2.1. Study sites for Tr. japonicus releases in 2019 (solid fill) and in 2020 (pattern fill) in lower Michigan. 
Different shaded circles indicate the 4 regional blocks each year within which sites were assigned to different Tr. 
japonicus release treatments. In 2019, sites received either 0 (control), 100 or 900 adult parasitoids as part of a 
single release. In 2020, sites received either 0 (control) or 500 in a single release or 250 individuals first and then an 
additional 50 at a second release date. The four underlined release numbers indicate the sites where Tr. japonicus 
was recaptured in 2020. For exact coordinates see Table. 2.1. 

 

 

Statistical analyses 

Halyomorpha halys sentinel eggs 

 

The rate of parasitism was assessed at the egg mass level by calculating the percentage of 

egg masses that yielded any parasitoids across the 12 sites of the 2019 and the 12 sites of the 

2020 releases. Parasitism rate on the individual egg level was calculated by using 28 eggs for the 

average size of an egg mass for H. halys. A generalized linear mixed model (GLMM) with 

binomial distribution (emergence vs. no emergence) and logit link function was used to assess 

 

16 

differences in parasitism rates between frozen and fresh sentinel eggs and those placed either 

lower or higher in the canopy in 2019. Height and the state of eggs were fixed variables and 

block was a random variable.  

 

Linear mixed models were used to assess how the state of the H. halys sentinel eggs 

(fresh or frozen), their placement (low or higher), and sampling date (month) may influence the 

number and species identity of emerging parasitoids (both native and Tr. japonicus) in 2019. 

Fixed effects in the model included date, placement, state of the eggs and parasitoid species 

identity. All interactions were non-significant (at α = 0.05) and did not improve AIC values, 

therefore were not included in the final model. These analyses were done only for 2019 because 

in 2020 parasitoid captures were very low. Emerging parasitoid numbers were log transformed to 

meet the model assumption of normal distribution and block was included as a random effect. 

The correlation between the number of egg masses attacked and the number of H. halys captured 

at each study site in 2019 was assessed using a linear regression. 

 

Podisus maculiventris sentinel eggs 

 

The rate of parasitism was assessed at the egg mass level by calculating the percentage of 

egg masses that yielded any parasitoids across the four sites where 900 Tr. japonicus had been 

released and where P. maculiventris sentinel eggs had been deployed. Parasitism rate on the 

individual egg level was calculated by using 14 eggs for the average size of an egg mass 

(Legaspi 2004).  

 

 

 

17 

Yellow sticky traps 

 

Generalized linear mixed models with binomial distribution and logit link function were 

used to compare parasitoid capture success (yes or no) of traps placed at different heights at the 

2019 and 2020 release site separately. Height and the state of eggs were fixed variables and 

block was a random variable. The number of captured parasitoids by traps placed lower or higher 

was compared using linear mixed models. Fixed effect in the model was the placement (low vs. 

high) and block was included as a random variable.  

 

 

Pyramid traps 

 

 A general linear model was used with sampling date (2019 or 2020 categorical variable), 

block and their interactions as fixed effects to compare the number of H. halys captured in 2019 

and 2020 at the 2019 release sites. Only data for the months of June, July and August were 

included in the analysis when monitoring efforts were similar between the years since 

monitoring stopped in early September in 2019 but continued through September in 2020. Block 

(groups of three sites in proximity; see Table 2.1) was included as a fixed effect to assess 

quantitatively regional differences in H. halys numbers. A similar analysis was conducted for 

stink bug captures at the 2020 release sites with block as a fixed factor. Stink bug numbers were 

log transformed (Log + 0.5) to meet model assumption of normal distribution. All analyses were 

performed using JMP Pro Version 13.0.0 (SAS Institute 2016). 

 

 

 

18 

Results  

 Halyomorpha halys sentinel eggs  

 

In 2019, 840 H. halys sentinel egg masses were deployed and 727 were successfully 

retrieved. Parasitoids emerged from 30 egg masses from 9 of the 12 study sites (Table 2.2). This 

constitutes 4.12% parasitism rate on the egg mass level over all sites, egg types and placements. 

A total of 241 parasitoids emerged from the parasitized egg masses resulting in 1.18% parasitism 

rate on the individual egg level. More than one parasitoid species emerged from three of the 30 

egg masses parasitized in 2019. For those three observations the number of emerged parasitoids 

were divided equally between the two species and were included as such in the dataset.  

 

In 2019, there was no difference in parasitism success of frozen versus fresh sentinel eggs 

(F = 3.5286 df = 1, 724 p = 0.0607) or eggs placed lower or higher in the canopy (F = 0.4713, df 

= 1, 720.7, p = 0.4926). The placement of eggs (F  = 0.3636, df = 1, 24.35, p = 0.5521), the date 

(F  = 0.6433, df = 2, 24.55, p = 0.5342) or the species identity of parasitoids (F  = 0.8981, df = 3, 

24.14, p = 0.4565) did not influence the number of emerging parasitoids (Figure. 2.2). However, 

more parasitoids emerged from frozen (non-transformed mean = 9.1 ± 1.91 SE) than from fresh 

(4.16 ± 2.12) eggs (F = 5.4686, df = 1, 23.79, p = 0.0281) (Figure. 2.3, Table 2.2). The number 

of H. halys captured over the season and the number of sentinel egg masses attacked at each site 

were positively correlated at the 2019 release sites (R2 = 0.61, p = 0.0027) (Figure. 2.4).   

 

 

 

19 

Table. 2.2. Outcome of monitoring using H. halys and P. maculiventris sentinel egg masses deployed at 12 field 
sites each in 2019 and 2020. 
 

  

Sentinel eggs deployed 

Sentinel eggs retrieved 

2019 Release 

H. halys 

840 

727 

Sentinel eggs placed lower (1.5 m) 

371 (51%) 

2020 Release 

P. 
maculiventris 

H. halys 

285 

133 

0 

430 

321 

168 (52%) 

Sentinel eggs placed higher (3.5 m) 

356 (49%) 

133 (100%) 

153 (48%) 

Frozen sentinel eggs 

Fresh sentinel eggs 

532 (73%) 

195 (27%) 

39 (30%) 

321 (100%) 

133 (70%) 

0 

Egg masses parasitized 

30 (4.12%) 

3 (2.26%) 

6 (1.87%) 

Sentinel eggs placed lower parasitized 

17 (57%) 

0 

Sentinel eggs placed higher parasitized 

13 (43%) 

Frozen egg masses parasitized 

Fresh egg masses parasitized 

17 (57%) 

13 (43%) 

Number of emerging parasitoids 

241 

3 (100%) 

2 (67%) 

1 (33%) 

12 

Parasitoids emerging from frozen eggs 

171 (71%) 

10 (83%) 

Parasitoids emerging from fresh eggs 

70 (29%) 

Parasitism rate on egg level 

1.18% 

2 (17%) 

0.60% 

2 (33%) 

4 (67%) 

6 (100%) 

0 

39 

39 

0 

0.43% 

 
 
 

In 2019, all emerging parasitoids were native species representing three families and four 

genera: Telenomus (Scelionidae), Trissolcus (Scelionidae), Anastatus (Eupelmidae) and 

Ooencyrtus (Encyrtidae). The number of emerging parasitoids were as follows: Anastatus spp. n 

= 97, Tr. euschisti (Ashmead) n = 55, Te. podisi Ashmead n = 40, and Ooencyrtus spp. n = 29 

(Figure. 2.5).   

 

In 2020, of the 430 H. halys sentinel egg masses deployed, 321 were retrieved. Six egg 

masses yielded a total of 39 parasitoids for 1.87% parasitism rate at the egg mass and 0.43% 

parasitism on the individual egg level across all sites (Table 2.2). Trissolcus japonicus emerged 

from one egg mass (n = 7) that was deployed on July 30 in a mixed orchard in Flint, Michigan 

following augmentative releases of 500 adults on July 1st. Trissolcus euschisti emerged from 

 

20 

three egg masses (n = 24), Te. podisi from one egg mass (n = 2) and Encyrtidae spp. from one 

egg mass (n = 6) (Figure. 2.2). 

 

Podisus maculiventris sentinel eggs 

 

Of the 285 P. maculiventris sentinel egg masses deployed in 2019, 133 were retrieved 

successfully. Three yielded 12 total parasitoids resulting in 2.25% parasitism rate of egg masses 

across all sites. Parasitism rate on the individual egg level was 0.6%. All parasitoids emerging 

from P. maculiventris eggs were native species from the genera Telenomus (n = 11) and 

Ooencyrtus (n = 1). 

 

Yellow sticky traps 

 

Of the 384 yellow sticky traps placed at the 12 field sites in 2020 where parasitoids had 

been released in 2019, 51 captured parasitoids that are likely to attack stink bugs. Encyrtidae spp. 

were captured most often (n = 46), followed by Tr. euschisti (n = 14), Te. podisi (n = 11), Tr. 

thyantae (Ashmead) (n = 2), Tr. brochymenae (Ashmead) (n = 2), Anastatus spp. (n = 2) and an 

unidentified Trissolcus spp. (n = 1). Trissolcus japonicus was captured at a single location close 

to Sparta, Michigan where 900 individuals had been released in 2019 (Figure. 2.5). The number 

of parasitoids captured by traps placed lower or higher in the canopy did not differ (F = 0.8447, 

df = 1, 379.1, p = 0.3587). 

 

Of the 400 yellow sticky traps placed at the 12 study sites in 2020 where parasitoids had 

been released in 2020, 69 captured parasitoids that likely attack stink bugs. The parasitoid 

 

21 

species captured were similar to that captured in 2020 at the 2019 release sites with Encyrtidae 

being most numerous (n = 62), followed by Tr. euschisti (n = 19), Te. podisi (n = 8), Anastatus 

spp. (n = 3), Te. persimilis Ashmead (n = 1) and Tr. brochymenae (n = 1) (Figure. 2.5). 

Trissolcus japonicus was recaptured at two sites, one where 250 and later 50 individuals had 

been released close to Washington, Michigan and at a control site that is located just 4.3 km from 

the Washington release site. The number of parasitoids captured by traps placed lower or higher 

in the canopy did not differ (F = 0.0176, df = 1, 395, p = 0.8945). 

Figure. 2.2. Total number of parasitoids of five species (or genera) emerging from H. halys sentinel eggs. The year 
of sampling is shown at the top of the graph. Parasitoids were released and monitored using sentinel eggs in 
southwestern Michigan in 2019 (left panel) and in southeastern Michigan in 2020 (right panel). There was no 
difference in the mean number of parasitoids emerging between months (p = 0.5342) or for the different parasitoid 
species (p = 0.4565) in 2019. Note that releases and sampling took place later in 2020 than in 2019 and only frozen 
eggs were used in 2020 for monitoring, which may explain the relatively lower parasitoid captures.     

 

 

22 

Figure. 2.3. Mean (± SE) number of parasitoids emerging from frozen or fresh H. halys sentinel eggs deployed in 
2019. Across species more parasitoids emerged from frozen than from fresh sentinel eggs (p = 0.0281) but within 
parasitoid species there was no difference between numbers emerging from frozen versus fresh eggs. 

 

 

23 

Figure. 2.4. The relationship between the number of H. halys sentinel egg masses parasitized and the number of H. 
halys captured by pyramid traps at the 12 study sites in 2019 (R2 = 0.61). Dotted lines represent 95% confidence 
interval curves.  
 

 

 

 

 

 

 

24 

Figure. 2.5. Parasitoid captures by yellow sticky traps in 2020 at 12 study sites where Tr. japonicus was released in 
2019 (left panel) and 12 sites where released in 2020 (right panel). Traps were changed every 3 weeks at the 2019 
release sites and every 2 weeks at the 2020 release sites. To display monthly total captures the number of parasitoids 
captured by each trap was divided in proportion of the number of days spent in the field for and given month.   
 

 

Halyomorpha halys numbers 

 

Halyomorpha halys densities across the 12 sites where Tr. japonicus had been released in 

2019 were higher in 2020 (non-transformed mean: 6.4 ± 1.18 SE) than in 2019 (1.12 ± 0.97) 

(year: F = 33.5459, df = 1, p < 0.0001). There were also regional differences in H. halys densities 

among sites (block: F = 21.5173, df = 3, p < 0.001). The mean H. halys captures were 

significantly lower in block 2 (the three sites in the Grand Rapids region; see Table 2.1 and 

Figure. 2.1) (non-transformed mean: 0.052 ± 0.05 SE) than the other three blocks at the 2019 

release sites (block 1: 6.15 ± 1.58, block 3: 5.27 ±  1.52, block 4: 3.58 ± 1.52) (Figure. 2.6). H. 

 

25 

halys captures were  higher at three of the four blocks in 2020 than in 2019, but in block two 

they remained low (block x year interaction: F = 2.8, df = 3, p = 0.0048).  

 

There were also regional differences in H. halys densities at the 2020 release sites (block: 

F = 10.8042, df = 3, p < 0.0001). Block five, that included sites around Flint, Michigan (see 

Table 2.1 and Figure. 2.1) had significantly higher H. halys densities (50.8 ± 7.2) than the other 

blocks (block 6: 9.22 ± 7.2, block 7: 10.83 ± 7.2, block 8: 7.6 ± 7.2) (Table 2.1, Fig 2.1).  

Figure. 2.6. Mean number of H. halys captured by pyramid traps at sites where Tr. japonicus was released either in 
2019 or 2020. The 2019 release sites were sampled both in 2019 and 2020 (2019 West and 2020 West). The 2020 
release sites were sampled in 2020 (2020 East). For the 2019 release sites more H. halys was captured in 2020 than 
in 2019 between June and August. Here mean captures are shown for the entire sampling season, which ended in 
early September in 2019 but continued until the end of September in 2020. 

 

 

 

 

 

26 

Discussion 

 

The importance of release size or release frequency mediating establishment of the egg 

parasitoid Tr. japonicus could not be determined during the course of this two-year study 

because of low recapture rates. Of the 7,200 adult parasitoids released over two years only 10 

individuals were recaptured at four of the 24 study sites (Figure. 2.1). In 2020, Tr. japonicus was 

found on one yellow sticky trap at a site where 900 individuals had been released a year prior. 

This could indicate successful overwintering. For the 2020 releases, Tr. japonicus was 

recaptured at three sites each representing a different release treatment (0, 250+50, or 500 

individuals). The emergence of seven individuals from an H. halys sentinel egg mass shows that 

Tr. japonicus is reproducing and the yellow sticky trap captures indicate summer activity and 

dispersal.  

 

The release sizes used in 2019 and 2020 at individual sites that ranged from 100–900 

(Table. 2.1, Figure. 2.1) are comparable to other studies testing the importance of release size of 

parasitoids for establishment. For example, 1, 10, or 100 female N. typhlocybae were introduced 

against a planthopper in southern France (Fauvergue et al. 2007) and 100–1000 To. sinensis were 

released at each site against the chestnut gall wasp (Borowiec et al. 2018). Both the above studies 

with N. typhlocybae and To. sinensis found parasitoid establishment and increasing population 

sizes in the same year and one or two years after the original releases (Borowiec et al. 2018; 

Fauvergue et al. 2007). However, our results that show very limited distribution and density of 

Tr. japonicus a few years after initial detection are not unusual. For example, a 2017 study in 

New Jersey that placed 236 sentinel eggs in commercial peach and apple orchards, similarly to 

this study, found only three egg masses parasitized by Tr. japonicus (Kaser et al. 2018). In 

Virginia only three of the 135 sentinel egg masses were parasitized by Tr. japonicus in 2016 

 

27 

(Quinn et al. 2019). These studies, conducted within two to three years of the initial detection of 

Tr. japonicus in nearby Maryland in 2014 (Talamas et al. 2015), indicate very low densities 

within a few years after discovery.  

 

Population growth of introduced populations can be impeded by a multitude of 

environmental, demographic and genetic factors (Fauvergue et al. 2012). Small introduced 

populations are subject to environmental and demographic stochasticity that can cause large 

fluctuations in population sizes and can lead to extinction (Fauvergue et al. 2012; Lande 1988; 

Lande 1993). Allee effects, whereby at low population densities individuals have lower survival 

or mating success, can slow population growth and can also lead to extinction (Courchamp et al. 

2008; Courchamp et al. 1999; Lande 1998). Introduced populations often go through bottlenecks 

that can reduce genetic diversity, adaptive potential and population growth as well (Fauvergue et 

al. 2012). Thus, it is not surprising that Tr. japonicus densities in Michigan are still low given its 

initial discovery in 2018 (Jarrett et al. 2019), followed by two years of augmentative releases.  

 

The climate in Michigan is predicted to be within the ‘highly’ and ‘moderately’ suitable 

range for Tr. japonicus establishment (Avila and Charles, 2018), therefore it is unlikely that 

abiotic conditions would prevent its widespread establishment. In fact, Tr. japonicus population 

growth appears quicker on the west coast of the USA, that is deemed only as ‘marginally’ 

suitable for establishment by climate models (Avila and Charles, 2018). In Washington state, 

where Tr. japonicus was first detected in 2015 (Milnes et al. 2016), a study conducted in 2017 

found that 67% of sentinel egg masses and 77% of individual H. halys eggs had been parasitized 

(Milnes and Beers, 2019). This may suggest that a ‘marginally’ suitable climate is not hindering 

population buildup of Tr. japonicus orthat this climate model have underestimated the optimal 

range of Tr. japonicus (Avila and Charles, 2018)  

 

28 

 

Trissolcus japonicus establishment and population growth in Michigan may have been 

impacted by the low density of H. halys in 2019 (Figure. 2.6). Spring 2019 was unusually cold 

and wet that could have caused mortality or delayed development of H. halys, which might 

partly explain the lack of Tr. japonicus captures that year. There is some evidence that even 

native parasitoid captures by H. halys sentinel eggs are positively correlated with H. halys 

density (Figure. 2.4), which suggest that parasitoids tend to accumulate where stink bug 

populations are higher. However, the most likely explanation for the lack of recapture in 2019 

and the low recapture rates in 2020 is that Tr. japonicus densities are very low across Michigan 

and within one to two years the released 7,200 adults cannot build up large enough populations 

that are reliably detectable with sentinel eggs or yellow sticky traps.  

 

The native parasitoid community, representing four genera (Trissolcus, Anastatus, 

Telenomus, and Ooencyrtus) that attacked H. halys sentinel eggs in Michigan is similar to those 

found across North America (Abram et al. 2017). Average rates of parasitism by native 

parasitoids that were between 1.87–4.12% at the egg mass level and 0.43–1.18% at the 

individual egg level in Michigan also align well with results of a review that found that in 87% 

of surveys the parasitism levels were under 5% (Abram et al. 2017). In our surveys, more 

parasitoids emerged from frozen than from fresh H. halys eggs, but the likelihood of parasitism 

did not differ between frozen and fresh eggs (Figure. 2.3). In Maryland, surveys also found 

higher emergence from frozen eggs, which may be explained by the lack of adaptation by native 

parasitoids to the immune response presented by viable H. halys eggs (Herlihy et al. 2016). 

However, a review of 98 datasets for parasitism by native species did not find any difference in 

attack rates between fresh and frozen sentinel eggs (Abram et al. 2017).  

 

29 

 

Parasitoid activity did not exhibit a distinct trend across the season as both the sentinel 

egg and yellow sticky trap captures showed varying peaks of activity among the study sites and 

sampling years (Figures. 2.3, 2.6). In Delaware, the rate of parasitism was positively correlated 

with average temperatures and the warmest month, July, was found to yield the highest 

parasitism rates (Dieckhoff et al. 2017). On the other hand, parasitism rates in Maryland steadily 

increased over the season, peaking in early September (Jones et al. 2017). A recent study 

indicated that Tr. japonicus captures are most likely in the middle and upper canopy of trees, 

while native parasitoids may be captured at any location (low, mid, or upper canopy) (Quinn et 

al. 2019). Our results corroborate that native parasitoids are equally likely to be captured both in 

the low and mid-canopy. However, three of our four Tr. japonicus recaptures occurred at 1.5 m 

height, which does not support the recommendation to sample only in the mid and high canopy 

for Tr. japonicus (Quinn et al. 2019). These discrepancies indicate that it may be difficult to 

generalize patterns with regards to when peak parasitism is expected, whether fresh or frozen 

eggs are more likely to be attacked, and at which heights parasitism by native or exotic 

parasitoids may be more prevalent. Differences in climate, site characteristics, sampling methods 

and a multitude of other factors between studies may account for the different findings. 

However, there is general agreement across studies that the current rates of egg parasitism by 

native parasitoids is unlikely to provide sufficient biological control to suppress H. halys 

populations (Abram et al. 2017; Cornelius et al. 2016; Dieckhoff et al. 2017; Jones et al. 2014; 

Ogburn et al. 2016; Rice et al. 2014). 

 

While Tr. japonicus is considered the most promising biocontrol agent because of its high 

parasitism rates of 50–80% of H. halys eggs in the native range (Yang et al. 2009; Zhang et al. 

2017), there are concerns regarding potential non-target effects. Host-specificity tests in the 

 

30 

laboratory have revealed that Tr. japonicus can attack over ten native stink bug species (Botch 

and Delfosse, 2018; Hedstrom et al. 2017). Trissolcus japonicus was also recovered from native 

stink bug eggs from the field including from P. maculiventris, which is an important predatory 

stink bug in North America (Gariepy and Talamas, 2019; Milnes and Beers, 2019). We deployed 

over 100 P. maculiventris eggs at four sites where 900 Tr. japonicus had been released in 2019 

but only native parasitoids attacked those eggs. In a survey in 2018, when 51 P. maculiventris 

eggs were placed alongside H. halys sentinel eggs we also did not find parasitism by Tr. 

japonicus (Jarrett et al. 2019). However, given the low density of Tr. japonicus in Michigan 

these results may not be representative of its potential impact on native species and it should be 

reevaluated once population densities increase. Since parasitism of native stink bugs by Tr. 

japonicus appears much lower (0.4–8%) in the field than that of H. halys (77%) its redistribution 

continues within multiple states (Jentsch, 2017; Milnes and Beers, 2019). Trissolcus japonicus is 

expected to be an important component of integrated pest management programs targeting H. 

halys both in North America and in Europe (Abram et al. 2020) and the augmentative releases 

conducted as part of this study will likely contribute to its widespread establishment and 

population growth across Michigan. 

 

 

 

 

 

 

31 

CHAPTER 3: The effects of heat waves on Halyomorpha halys survival and parasitism 

success by Trissolcus japonicus 

 

Introduction 

 

Global climate change is leading to a rise in mean temperatures and increases in the 

frequency, length and intensity of extreme weather events, such as heat waves (Ebi and Meehl, 

207; Houghton, 2009; IPCC, 2012). Insects, like other ectotherms are particularly sensitive to 

temperature changes because they have limited ability for thermoregulation. Changes in 

temperature can directly affect the physiology and behavior of insects including development, 

movement, reproduction, and foraging abilities (Angilletta et al. 2002; Chown and Terblanche, 

2006). Gradual increases in temperature are predicted to benefit insects in temperate regions as it 

can lead to higher overwintering survival, extend seasonal activity windows and can result in the 

expansion of geographic ranges (Bale et al. 2002; Berg et al. 2010; Deutsch et al. 2008; Hickling 

et al. 2006; Musolin and Fujisaki, 2006; Parmesan, 1999). However, heat waves, defined as 

periods when maximum temperatures are above seasonal norms by 5˚C for at least 5 consecutive 

days (De Boeck et al. 2010), can cause direct mortality and can have negative fitness 

consequences for surviving individuals (Bannerman et al. 2011; Roux et al. 2010; Sentis et al. 

2013; Zhang et al. 2019).   

 

The susceptibility to thermal stress can vary between different trophic levels across a 

food chain (Aguilar-Fenollosa and Jacas 2014; Hance et al. 2007; Voigt et al. 2003). It is 

predicted that natural enemies (e.g. parasitoids and predators) will be more adversely affected 

than herbivorous insects, partly because they appear to have smaller thermal windows within 

which they can grow and reproduce (Aguilar-Fenollosa and Jacas, 2014; Hance et al. 2007; 

 

32 

Montserrat et al. 2013; Schreven et al. 2017), however, the evidence for these expectations is 

contradictory. For example, the parasitoid wasp Aphidius avenae Haliday (Hymenoptera: 

Braconidae) suffered high mortality after one hour of exposure to a heat stress event of 36˚C and 

the surviving individuals had lower fecundity (Roux et al. 2010). On the other hand, heat waves 

of up to 40˚C imposed over a 7-day period reduced aphid population growth but did not affect 

the fecundity of the parasitoid Aphidius matricariae Haliday (Hymenoptera: Aphidiidae) 

(Bannerman et al. 2011). In a tri-trophic system, the biomass of sweet pepper plants did not 

change, the abundance and fecundity of the aphid Myzus persicae Sulzer (Homoptera: 

Aphididae) were reduced, and  development time of the ladybeetle Coleomegilla maculata lengi 

Timberlake (Coleoptera: Coccinellidae) increased and larval weight decreased in response to 

heat waves (Sentis et al. 2013). Thus, the responses can vary widely depending on species, the 

community context and differences in experimental procedures.  

 

Even if the direct effects of heat stress are not necessarily detrimental to natural enemies, 

they can still be affected by heat waves to a larger extent than herbivores because of ‘bottom-up 

amplification’ effects from the lower trophic levels (Anguilar-Fenollosa and Jacas, 2014). Higher 

trophic levels have to cope not only with the direct effects of heat waves but also the indirect 

effects stemming from the differential responses of lower trophic levels to the same heat stress, 

which can alter trophic and other ecological interactions (Anguilar-Fenollosa and Jacas, 2014). 

Within higher trophic levels the vulnerability of different groups also varies. Generalist predators 

that can easily switch between prey are predicted to be less sensitive to changes in trophic 

interactions than specialist parasitoids with narrow host ranges whose development is tightly 

linked to the phenology of their hosts (Foden et al. 2008). In addition, the effectiveness of 

parasitoids can further be reduced because of changes in host resistance with increasing 

 

33 

temperatures. For example, parasitism was shown to be less effective at higher temperatures in 

Spodoptera littoralis Boisduval (Lepidoptera: Noctuidae) by the braconid wasp Microplitis 

rufiventris, Kokujev (Hymenoptera: Braconidae) and also in Drosophila melanogaster Meigen 

(Diptera: Drosohilidae) by Asobara tabida Nees von Esenbeck (Hymenoptera: Braconidae) 

(Fellows et al. 1999; Hegazi and Khafagi, 2005). Because of the asymmetrical effects of climate 

change on natural enemies and herbivores, biological control services provided by higher trophic 

levels can be disrupted. This is especially important in the case of invasive insects that have 

relatively few natural enemies in the introduced range.  

 

In this study, we evaluated the sensitivity of an invasive insect, the brown marmorated 

stink, Halyomorpha halys Stål (Hemiptera: Pentatomidae) and one of its natural enemies, the 

parasitoid Trissolcus japonicus Ashmead (Hymenoptera: Scelionidae) to stimulated heat waves. 

Halyomorpha halys occupies a large geographic range, as it is native to Asia and has invaded 

North America, Europe, and more recently, South America (Faundez and Rider 2017; Haye et al. 

2015; Lee et al. 2013; Leskey and Nielsen 2018). It is highly polyphagous feeding on over 100 

plant species including economically important crops (Lee et al. 2013; Leskey and Nielsen 

2018). Optimal development of H. halys occurs between 25-30˚C and it cannot complete 

development when kept below 15˚C or over 35˚C (Haye et al. 2014; Nielsen et al. 2008).  

 

Trissolcus japonicus, is a solitary oligophagous endoparasitoid that attacks eggs of 

several stink bug species within the family Pentatomidae (Botch and Delfosse 2018; Haye et al. 

2020; Hedstrom et al. 2017; Yang et al. 2009). It is native to Asia and was accidentally 

introduced to North America and Europe (Stahl et al. 2019; Talamas et al. 2015). It is one of the 

most important egg parasitoids of H. halys in its native range with parasitism rates of 50-80% 

(Yang et al. 2009). The optimal development window of Tr. japonicus is between 27-30˚C with 

 

34 

an upper threshold of 36˚C beyond which no development had been observed (Li and Liu 2004; 

Qiu et al. 2007). While the developmental thresholds for H. halys and Tr. japonicus are similar 

(35 and 36˚C) it is unknown how intermittent heat stress beyond these upper limits will impact 

either species. Since Tr. japonicus is considered the most promising biological control agent of 

H. halys in the introduced range it is important to explore how survival of both species and 

parasitism rates may be impacted by heat waves.  

 

We simulated heat waves of varying intensity (36 – 42˚C), applied for 4 hours during the 

afternoon of five consecutive days and assessed emergence of H. halys and Tr. japonicus from 

unparasitized and parasitized H. halys eggs, respectively. We also evaluated how heat waves 

may affect parasitism rates by exposing adult female Tr. japonicus with H. halys eggs to the 

same heat waves. In addition, we measured post-generational effects by assessing parasitism 

success of the offspring of wasps exposed to heat waves. We predicted that the parasitoid will be 

more sensitive than the herbivore to heat waves based on expectations regarding differential 

responses of different trophic levels. 

 

Materials and Methods 

Background on study species  

 

Halyomorpha halys overwinters as adults and terminates diapause at 12.7 hours of 

photoperiod (Nielsen et al. 2017). Reproductive development is mediated by temperature and 

differs between locations with oviposition commencing anywhere between 150 – 450 growing 

degree days (May/June in temperate climates) assuming 14.17˚C as the lower developmental 

threshold (Nielsen et al. 2017; Nielsen et al. 2008). Females lay on average 244 eggs with a 

median of 28 eggs per cluster over a period of four months (Nielsen et al. 2008). Eggs hatch in a 

 

35 

week, and development proceeds through five instars with adult emergence within 41 – 48 days 

at 25˚C (Nielsen et al. 2008). In the invaded range H. halys typically completes one generation a 

year but as it spreads south it can become multivoltine (Nielsen et al. 2008).  

Trissolcus japonicus overwinters as adults and can start development at 12.2˚C but most 

growth takes place at temperatures between 18 and 33˚C (Li and Liu 2004; Qiu et al. 2007). 

Females prefer to oviposit in stink bug eggs that are 1 – 3 days old and lay 42 eggs on average 

over their lifetime (Yang et al. 2009). Egg to adult development can be completed within 12 days 

at 25˚C resulting in up to 10 generations in a year in the native range in subtropical areas and 

multiple generations in temperate regions including in North America (Avila and Charles, 2008; 

Yang et al. 2018).  

 

Insect rearing 

Halyomorpha halys egg masses used for the experiments were either shipped from the 

Phillip Alampi Beneficial Insect Laboratory (New Jersey Department of Agriculture, Trenton, 

NJ) or came from a rearing at Michigan State University (MSU) that was initiated from eggs 

from the above source. In the MSU labs H. halys were kept in mesh cages (40 x 20 x 20 cm) 

(Educational Science, League City, TX, U.S.) at 25˚C and 60-75% humidity with a photoperiod 

of 16:8 L:D in a climate-controlled room. They were given water through dental wicks (Dynarex 

N/S #2 Medium) and raised on a diet of organic green beans, snap peas, broccoli, carrots, apples, 

and mixed nuts.  

Trissolcus japonicus used for the experiments originated from a laboratory rearing at 

MSU. The colony was founded by two males and three females that were captured on MSU 

campus in August 2018 by a H. halys sentinel egg mass (Jarrett et al. 2019). Adults were kept in 

 

36 

10-dram plastic vials at 20˚C and 70% humidity with a photoperiod of 16:8 L:D in groups of 10-

20 with a drop of honey for provision. One or two H. halys egg masses were offered for 

oviposition to 5-10 wasps for three days then placed in a new vial. Parasitoids took 14-20 days 

under these conditions to complete development.  

 

Experimental design 

Three experiments were conducted to evaluate the effects of heat waves on early life 

stages of H. halys and Tr. japonicus and on parasitism success of H. halys by Tr. japonicus. In 

Experiment 1, the impacts of heat waves on H. halys emergence were evaluated by exposing 

unparasitized H. halys egg masses to heat waves. In Experiment 2, the impacts of heat waves 

were evaluated on H. halys eggs parasitized by Tr. japonicus. In Experiment 3, the impact of 

heat waves on parasitism of H. halys eggs by Tr. japonicus were evaluated by exposing fresh H. 

halys eggs together with one Tr. japonicus female. These three experiments were run at the same 

time within the same climate chambers for given temperature treatments. Experiments 1 and 2 

were repeated in a second independent trial and will be referred to as Experiment 1 trial 2 and 

Experiment 2 trial 2.  

Two additional experiments were conducted to assess transgenerational effects of heat 

waves by evaluating the performance of the offspring of Tr. japonicus that had been exposed to 

heat waves. Experiment 4 used Tr. japonicus adults that emerged from parasitized H. halys eggs 

that were exposed to heat waves as part of Experiment 2, and Experiment 5 used Tr. japonicus 

adults that emerged from H. halys eggs that were parasitized during heat waves as part of 

Experiment 3.    

 

37 

For Experiments 1-3, five different heat wave treatments were applied: 25˚C (control), 

36˚C, 38˚C, 40˚C, and 42˚C, for four hours between 12 – 4 pm for five consecutive days. 

Temperatures were returned to 25˚C following the heat wave treatments. Heat wave treatments 

were chosen to represent a range around the highest temperature (40.5˚C) recorded in Grand 

Rapids, Michigan based on data from www.weatherbase.com for the years 2014 - 2019. A 

completely randomized design was used with eight replications for each heat wave treatments for 

Experiments 1-3 and in the second trials of Experiments 1-2. The number of replications varied 

for Experiments 4 and 5 and will be described in the below subsections. 

 

Experiment 1: Impact of heat waves on H. halys emergence 

To assess the impact of heat waves on H. halys emergence, fresh H. halys eggs (< 72 h) 

were exposed to the above described heat wave treatments. Eggs were placed in 60 x 15 mm 

stackable Petri dishes (VWR®) in temperature-controlled incubators that were kept at 16:8 L:D 

photoperiod and 50-65% humidity. Emergence success and the number of emerging first instar 

H. halys nymphs were recorded during and for four days following the heat wave treatments. 

This experiment was repeated in two independent trials.  

 

Experiment 2: Impact of heat waves on H. halys eggs parasitized by Tr. japonicus 

To assess the impact of heat waves on Tr. japonicus development and emergence, H. 

halys eggs that had been parasitized by Tr. japonicus five days prior to the start of the 

experiment were exposed to the above described heat wave treatments. The experimental 

procedures were the same as described for Experiment 1. Emergence success and the number of 

 

38 

emerging adults were measured in both the first and second trials. In addition, development time 

of Tr. japonicus was assessed in the first trial.  

 

Experiment 3: Impact of heat waves on H. halys egg parasitism by Tr. japonicus 

To assess the impact of heat waves on parasitism success by Tr. japonicus, one fresh (< 

72 h old) H. halys egg mass together with one adult female Tr. japonicus were exposed to heat 

wave treatments. The experiments took place in 120 ml deli cups with a fine mesh top to allow 

air flow. A 4 cm long dental wick remoistened every day, and a green bean leaf with a drop of 

honey were placed in each cup to provide water, shelter and provision for the parasitoids. The 

heat wave treatments were as described previously. Egg masses were followed for 4 weeks and 

the development time, development success (or emergence success) and the number of adult Tr. 

japonicus emerging were recorded. In addition, the survival of female Tr. japonicus individuals 

used for parasitism was monitored during the 5-day exposure to heat waves. Adults surviving 

past the heat waves were kept at 25˚C for three days and then a fresh H. halys egg mass was 

given to each for five days to assess the effects of heat waves on their ability for further 

parasitism. Emergence success and the number of emerging Tr. japonicus was monitored from 

these egg masses. 

 

Experiments 4 and 5: Transgenerational effects 

To measure carry-over or transgenerational effects of heat waves one adult female 

parasitoid was randomly chosen from each replication that had adult Tr. japonicus emergence 

from egg masses parasitized prior to (Experiment 2 trial 1) or during (Experiment 3) heat waves. 

Experiment 4 refers to transgenerational effects resulting from Experiment 2 and Experiment 5 

 

39 

refers to transgenerational effects resulting from Experiment 3. Each female wasp was given one 

H. halys egg mass to parasitize for five days at ambient temperatures and parasitized eggs were 

kept at 25˚C, 16:8 L:D photoperiod and 50-65% humidity in a climate chamber. Emergence 

success and the number of emerging Tr. japonicus were monitored from these egg masses for 

four weeks. The number of replications varied between temperature treatments for both 

Experiments 4 and 5 and depended on the number of replications from which Tr. japonicus 

adults successfully emerged in Experiments 2 and 3, respectively. The number of replications is 

shown in Figure. 3.11.  

 

Statistical analyses 

Experiment 1: Impact of heat waves on H. halys emergence 

 

Binary logistic regression was used to compare the probability of successful emergence 

of H. halys nymphs from eggs exposed to the different heat wave treatments. The response 

variable was emergence success, coded as either 0 in case of no emergence or 1 if at least one 

individual emerged from an egg mass. Temperature was included as a continuous variable. To 

evaluate the accuracy of the logistic regression model the position of Receiver Operating 

Characteristic (ROC) curves were inspected and the area under the curve (AUC) index was 

evaluated. ROC curves resembling a diagonal line indicate inaccurate models. The further the 

ROC curves are from the diagonal line and the higher the AUC is (the closer to 1) the better 

predictive power the model has (SAS Institute 2016). Similar logistic regression models were 

used for all subsequent analyses for Experiments 2-5 where the response variable was binary (i.e. 

emergence success or no success, or survival versus no survival).  

 

40 

 

The number of nymphs emerging from the different heat wave treatments were compared 

using one-way ANOVA. For this analysis, replications both with and without any emergence 

were included and temperature was included as a categorical variable. Data for emergence counts 

were log transformed using base10(x+0.5) to meet the model assumption of normal distribution, 

but non-transformed means are used to visualize the results. Tukey’s HSD post hoc test was used 

to assess significant differences between temperature treatments. The two independent trials 

were analyzed separately. Similar one-way ANOVAs and post hoc tests were used for 

subsequent analyses for Experiments 2-5 to compare the number of emerging Tr. japonicus. All 

analyses were run in JMP Pro, version 13.0.0 (SAS Institute, 2016).  

 

Experiment 2: Impact of heat waves on H. halys eggs parasitized by Tr. japonicus 

 

Binary logistic regression, as described for Experiment 1, was used to compare the 

probability of successful emergence of Tr. japonicus from parasitized eggs exposed to the 

different heat wave treatments. One-way ANOVA, as described for Experiment 1, was used to 

compare the number of emerging Tr. japonicus adults between the different heat wave 

treatments. The two independent trials were analyzed separately. One-way ANOVA was used to 

compare development time of Tr. japonicus at different temperatures in trial 1 with temperature 

coded as a categorical variable.  

 

Experiment 3: Impact of heat waves on H. halys egg parasitism by Tr. japonicus 

 

The probability of successful emergence and the number of emerging adults of Tr. 

japonicus at the different heat wave treatments were evaluated with binary logistic regression 

and one-way ANOVA as described for Experiment 1. One-way ANOVA was used to compare 

 

41 

development time of Tr. japonicus when exposed as a 1-5 day of larvae to different heat waves 

with temperature coded as a categorical variable. The 5-day survival of Tr. japonicus females 

used for parasitism during heat waves was assessed with a binary logistic regression where those 

that survived to day five were coded as 1 and those that did not were coded as 0. The number of 

emerging offspring of females exposed to different heat waves were compared with one-way 

ANOVA as described for Experiment 1.  

 

Experiments 4 and 5: Transgenerational effects 

 

The probability of successful second-generation offspring emergence of mothers exposed 

to heat waves either as 5-10 days old larvae (Experiment 4) or 1-5 days old larvae (Experiment 

5) were evaluated using logistic regression as described for experiment one. The number of 

second-generation Tr. japonicus adults emerging for Experiment 4 and 5 in relation to maternal 

exposure to different heat waves were compared with one-way ANOVAs separately for the two 

experiments.  

 

Results 

Experiment 1: Impact of heat waves on H. halys emergence 

 

Halyomorpha halys egg emergence success was significantly reduced by heat waves in 

both the first (χ2=15.44, df = 1, p < 0.0001) (Figure. 3.1.A) and second trial (χ2=29.24, df = 1, p 

< 0.0001) (Figure. 3.1.B). Emergence success in the first trial, defined as at least one egg 

hatching from a cluster of 28 in a replication decreased to 25% at 36˚C, 12.5% at 40˚C and no 

emergence was observed at 42˚C (Figure. 3.1.A). In the second trial overall emergence rates 

were higher with at least a few nymphs emerging from all replicates at 36˚C with 50% survival 

 

42 

at 38˚C, 37.5% at 40˚C and no survival at 42˚C (Figure. 3.1.B). The number of emerging H. 

halys nymphs were negatively affected by heat waves in both the first (F4,3.05 = 7.448, p = 

0.0002) and second trials (F4,12.91 = 33.599, p < 0.0001) (Figure. 3.2).  

 

A

B

 

Figure. 3.1. Results of Experiment 1. Emergence success of H. halys nymphs from eggs exposed to an ambient 
temperature (25˚C) or four heat wave treatments (36, 38, 40, and 42˚C) in two independent trials (A: trial 1, B: trial 
2). The curve is the logistic regression curve that indicates the probability of successful emergence at the different 
temperature treatments. Dots are randomly jittered in a vertical position. Blue dots under the curve indicate 
replicated egg masses, each with 28 eggs, from which at least one nymph emerged. Red dots above the curve are 
replications without any adult emergence. The reference categories on the right y axis show the probability of 
successful (1) or unsuccessful emergence (0) across all temperature treatments.  

 

43 

 

Figure. 3.2. Results of Experiment 1. Mean (± SE) H. halys nymphs emerging from egg masses, each with 28 eggs, 
that were exposed to an ambient temperature (25˚C) or four heat wave treatments (36, 38, 40, and 42˚C) in two 
independent trials (Blue: trial 1, Red: trial 2). Letters indicate significant difference between temperatures within 
each trial.  

 

Experiment 2: Impact of heat waves on H. halys eggs parasitized by Tr. japonicus 

 

Trissolcus japonicus emergence success was negatively impacted by heat waves in both 

the first (χ2=17.20, p < 0.0001) (Figure. 3.3.A) and second trials (χ2=7.79, p = 0.0052) (Figure. 

3.3.B). The results of the two trials were similar showing adult emergence from all replicates 

exposed to 36 and 38˚C (Figure. 3.3.A). Emergence rates at 40˚C were 100% in trial 2, dropped 

only to 75% in trial 1, and even at 42˚C 37.5% of replications had adult emergence in trial 1 

(Figure. 3.3.B). The number of adults emerging was reduced by heat waves in both the first 

(F4,11.91 = 16.099, p < 0.0001) and second trials (F4,8.98 = 13.287, p < 0.0001). Adult emergence 

was similar at 25, 36, and 38˚ C in both experiments and only started to decrease at temperatures 

 

44 

of 40 and 42˚C (Figure. 3.4). Development time increased with increasing temperatures (F4,134.23 

= 20.713, p < 0.0001) taking almost twice as long at 42˚C than at 25˚C (Figure. 3.5).  

A

B

 

Figure. 3.3. Results of Experiment 2. Emergence success of Tr. japonicus from H. halys eggs that were parasitized 
prior to exposure to an ambient temperature (25˚C) or four heat wave treatments (36, 38, 40, and 42˚C) in two 
independent trials (A: trial 1, B: trial 2). The curve is the logistic regression curve that indicates the probability of 
successful emergence at the different temperature treatments. Dots are randomly jittered in a vertical position. Blue 
dots under the curve indicate replicated H. halys egg masses, each with 28 eggs, from which at least one adult Tr. 
japonicus emerged. Red dots above the curve are replications without any adult emergence. The reference categories 
on the right y axis show the probability of successful (1) or unsuccessful emergence (0) across all temperature 
treatments. 

 

 

 

 

45 

 

Figure. 3.4. Results of Experiment 2. Mean (± SE) number of Tr. japonicus adults emerging from H. halys egg 
masses, each with 28 eggs, that were parasitized prior to exposure to an ambient temperature (25˚C) or four heat 
wave treatments (36, 38, 40, and 42˚C) in two independent trials (A: trial 1, B: trial 2). Letters indicate significant 
difference between temperatures within each trial.  

 

 

Figure. 3.5. Results of Experiment 2 trial 1. Mean (± SE) development time (days) of Tr. japonicus exposed to an 
ambient temperature (25˚C) or four heat wave treatments (36, 38, 40, and 42˚C). Note that development time here is 
shown as the time between the first day of heat wave treatments and the first adult emergence. Eggs were parasitized 
five days prior to the start of the experiment. Letters indicate significant difference between temperatures. 

 

46 

 

Experiment 3: Impact of heat waves on H. halys egg parasitism by Tr. japonicus 

 

Trissolcus japonicus emergence success was similar across the different heat wave 

treatments (χ2=0.874, df = 1, p = 0.3498) with adults emerging from most replications exposed to 

different temperatures as 1-5 days old larvae (Figure. 3.6). The number of adults emerging 

differed among the different heat wave treatments (F4,3.5 = 2.853, p = 0.038), a pattern driven by 

significant difference in emergence rates only between 36˚C and 38˚C (Figure. 3.7). 

Development took significantly longer when parasitism took place during heat waves of 42˚C 

than at lower temperatures (F4, 141.02 = 21.067, p < 0.0001) (Figure. 3.8). The survival of adults 

exposed to heat waves decreased significantly with increasing temperatures (χ2=14.54, df = 1, p 

< 0.0001) with half of the females dying at 36˚C and all at 42˚C by day five of the experiment 

(Figure. 3.9). When adults that survived the 5-day exposure to heat waves were given a new H. 

halys egg mass to parasitize at ambient temperatures (25˚C) almost all the egg masses yielded 

similar numbers of adult Tr. japonicus (F3, 0.44 = 0.5287, p = 0.6689).  

 

 

47 

 

Figure. 3.6. Results of Experiment 3. Emergence success of Tr. japonicus from H. halys eggs that were parasitized 
during exposure to an ambient temperature (25˚C) or four heat wave treatments (36, 38, 40, and 42˚C). The curve is 
the logistic regression curve that indicates the probability of successful emergence at the different temperature 
treatments. Dots are randomly jittered in a vertical position. Blue dots under the curve indicate replicated H. halys 
egg masses, each with 28 eggs, from which at least one adult Tr. japonicus emerged. Red dots above the curve are 
replications without any adult emergence. The reference categories on the right y axis show the probability of 
successful (1) or unsuccessful emergence (0) across all treatments.  

 

Figure. 3.7. Results of Experiment 3. Mean (± SE) number of Tr. japonicus adults emerging from H. halys egg 
masses, each with 28 eggs, that were parasitized during exposure to an ambient temperature (25˚C) or four heat 
wave treatments (36, 38, 40, and 42˚C). Letters indicate significant difference between temperatures. 

 

48 

 

Figure. 3.8. Results of Experiment 3. Mean (± SE) development time (days) of Tr. japonicus exposed to an ambient 
temperature (25˚C) or four heat wave treatments (36, 38, 40, and 42˚C) in the first experiment. Eggs were 
parasitized during the heat wave treatments. Letters indicate significant difference between temperatures. 

 

 

Figure. 3.9. Survival of adult Tr. japonicus when exposed to an ambient temperature (25˚C) or four heat wave 
treatments (36, 38, 40, and 42˚C) for five days. The curve is the logistic regression curve that indicates the 
probability of successful emergence at the different temperature treatments. Dots are randomly jittered in a vertical 
position. Blue dots under the curve indicate females that survived and red dots above the curve indicate females that 
died by day five. The reference categories on the right y axis show the probability of successful (1) or unsuccessful 
emergence (0) across all temperature treatments. 

 

49 

Experiments 4 and 5: Transgenerational effects 

 

In Experiment 4, exposure of Tr. japonicus as 5-10 days old larvae to heat wave 

temperatures did not affect emergence success of the subsequent generation that developed at 

ambient temperatures (χ2=0.874, df = 1, p = 0.3498) (Figure. 3.10.A). The number of parasitoids 

emerging in the second generation was similar regardless of the different temperatures the 

mothers experienced during their early development (F4, 0.61 = 0.5372, p = 0.7096) (Figure. 

3.10.B). There was, however, a transgenerational effect both for emergence success (χ2=3.957, p 

= 0.0467) and in terms of the number of second-generation adults emerging (F4,4.91 = 5.14, p = 

0.0052) in Experiment 5, when the heat wave exposure occurred during parasitism and was 

experienced by 1-5day old Tr. japonicus larvae. Emergence success and the number of adults 

emerging declined in the second-generation with the severity of heat stress experienced by the 

mothers (Figures. 3.10.B, 3.11). Thus, the latter was driven by the lack of emergence at 42˚C 

while adult numbers were similar at all other temperatures. 

A

B

 

Figure. 3.10. Results of Experiments 4 and 5 testing transgenerational effects Second generation (F2) emergence 
rates of Tr. japonicus where the maternal generation (F1) was exposed either as 5-10 days (A – Experiment 4) or 1-4 
days old (B – Experiment 5) larvae to an ambient temperature (25˚C) or four heat wave treatments (36, 38, 40, and 
42˚C). Blue dots indicate replicated H. halys egg masses, each with 28 eggs, from which at least one adult emerged. 
Red dots are replications without any adult emergence. 

 

50 

Figure. 3.11. Results of Experiments 4 and 5 testing transgenerational effects. Mean (± SE) number of second-
generation (F2) Tr. japonicus adults emerging from mothers that were exposed either as 5-10 days (Experiment 4 - 
Blue) or 1-5 days (Experiment 5 - Red) old larvae to an ambient temperature (25˚C) or four heat wave treatments 
(36, 38, 40, and 42˚C). Letters indicate significant difference between temperatures within each experiment. 
Numbers above bars show the number of replications.  

 

 

Discussion 

 

Heat waves are predicted to have stronger negative effects on natural enemies than on 

herbivores. We found that the eggs of the herbivore, H. halys were more sensitive to heat waves 

than larvae of their egg parasitoid, Tr. japonicus. Heat waves did not reduce parasitism rates, but 

increased adult parasitoid mortality, and delayed development. We also detected trans-

generational effects, whereas the emergence success and number of adults produced by Tr. 

japonicus in the second generation was negatively correlated with the severity of heat waves the 

maternal generation had experienced as larvae.  

 

51 

 

We exposed H. halys eggs to varying levels of heat waves and found that emergence 

success declined sharply between 36 and 38˚C with very little survival beyond these 

temperatures (Figures.3.1, 3.2). It has been shown that increasing temperatures can reduce 

development time of H. halys eggs without much mortality up until 30˚C, but beyond this 

temperature egg mortality increases with no survival at 35˚C (Nielsen et al. 2008). It appears that 

even intermittent temperature increases beyond this upper limit can cause significant mortality 

indicating that the egg stage of H. halys is rather sensitive to heat stress. It is well-established 

that different insect life stages can have differing tolerance to heat stress and that the egg stage 

can be particularly vulnerable (Bowler and Terblanche, 2008; Chiu et al. 2015; Kingsolver et al. 

2011; Klockmann et al. 2017; Pincebourde and Casas, 2015). Thus, it is possible that nymph and 

adult stages of H. halys will be less sensitive to heat waves. 

  

The direct effects of heat waves may well be increased egg mortality of H. halys and 

associated indirect effects might also aid Tr. japonicus population growth. Yang et al. (2018) 

found that development time of Tr. japonicus was reduced, emergence rates were higher, and the 

sex ratio became more female-biased when developing in unfertilized H. halys eggs as opposed 

to fertilized eggs. These positive effects on development are likely due to the unfertilized eggs 

being inviable and thus lacking resistance to parasitism (Yang et al. 2018). If heat waves of as 

low as 36˚C result in high egg mortality, development success of Tr. japonicus attacking those 

eggs might increase leading to higher parasitoid population sizes with higher proportion of 

females in them. Thus, both the direct and indirect effects of heat waves may aid control of H. 

halys. However, it is unlikely that intermittent heat waves would result in significant reduction of 

H. halys populations because they lay eggs over a period of months, therefore only a small 

portion of eggs may be exposed to high temperatures at any given time. 

 

52 

 

The upper threshold for Tr. japonicus development is very close to that of H. halys (36˚C 

vs. 35˚C, respectively) (Haye et al. 2014; Li and Liu, 2004; Qiu et al. 2007; Nielsen et al. 2008), 

but overall Tr. japonicus appears less vulnerable to intermittent exposure to temperatures beyond 

this upper limit than H. halys. We found high survival rates of Tr. japonicus larvae at heat waves 

up to 40˚C with some emergence even after exposure to 42˚C (Figures. 3.3, 3.6). Older larvae (5-

10 days old) (Figures. 3.3, 3.4) was somewhat more susceptible than younger (1-5 days old) 

larvae, and parasitism success remained high during heat waves (Figures. 3.6, 3.7). Adult Tr. 

japonicus mortality increased with temperature with all females dying after 5 days of exposure to 

42˚C heat waves (Figure. 3.9). Nevertheless, the surviving adults were able to parasitize 

additional eggs without any apparent reduction in efficiency, even those exposed to 40˚C, and 

there was no difference in offspring survival. In contrast to our results, A. avenae females that 

were exposed to 36˚C just for one hour had significantly reduced aphid parasitism rates and their 

offspring had lower survival (Roux et al. 2010). However, parasitism rates of A. matricariae, 

another aphid parasitoid, were not affected by heat waves of up to 40˚C imposed for seven days 

(Bannermann et al. 2011), which are similar to our results.  

 

Development time of Tr. japonicus increased with temperature, almost doubling at 42˚C 

heat waves compared to 25˚C (Figures. 3.5, 3.8). At constant temperatures, development time in 

insects usually declines with increasing temperatures, however, this trend gets reversed close to 

the upper thermal limit (Liu et al. 1995; Ratte et al. 1984; Régnière et a. 2012). Our results align 

with this general trend since all our heat wave treatments were close to or beyond the upper 

thermal threshold for Tr. japonicus and accordingly we saw negative effects on development 

time. Few other studies looked at the effects of intermittent heat stress on development times in 

parasitoids (Gillespie et al. 2012; Schreven et al. 2017) so it is hard to generalize. In an 

 

53 

endoparasitoid of the cabbage moth, Diadegma semiclausum Hellén (Hymenoptera: 

Ichneumonidae), a 5˚C heat pulse decreased development time but a 10˚C heat pulse, which was 

closer to the developmental threshold, delayed development (Schreven et al. 2017). In two aphid 

parasitoids, A. abdominalis Dalman (Hymenoptera: Aphelinidae) and A. matricariae mummy 

formation of attacked aphids was delayed but development time only increased in A. matricariae 

under heat waves of 40˚C (Gillespie et al. 2012). Longer development time of parasitoids can 

increase their exposure to predation and to adverse abiotic conditions that may increase 

mortality, and it can reduce the number of generations they are able to complete lowering their 

biocontrol potential. Thus, depending on which life stage of Tr. japonicus is exposed, heat waves 

may have neutral or negative effects.  

 

Besides the direct impact of heat waves on the generation that is exposed, the experience 

of the parental generation can also carry over to the next generation. Such maternal effects or 

transgenerational effects are common in insects and have been shown to influence multiple life 

history traits including diapause, development time or offspring quality (Mousseau and Dingle, 

1991). We found that when adults were exposed to heat waves during parasitism (F0), not only 

was the offspring they produced impacted by heat waves (F1) but the next generation produced 

by that offspring as well (F2). First, the survival of F0 adults was decreased by heat waves 

(Figure. 3.10). In their offspring (F1), developmental success appeared unchanged (Figure. 3.11), 

however, their development time increased with the intensity of heat waves they experienced as 

1-5 day old larvae (Figure. 3.8). Finally, in the next generation (F2) that the F1 offspring 

produced emergence rates and the number of emerging adults declined in relation to the severity 

of heat stress their parental generations (F0 and F1) experienced (Figures. 3.10, 3.11). There are 

few examples for transgenerational effects of heat stress in insects and little is known of the 

 

54 

mechanisms mediating such effects (Ismaeil et al. 2013; Ma et al. 2020; Sales et al. 2019). The 

aphid parasitoid A. ervi showed similar responses as Tr. japonicus, in that, the adults had reduced 

survival and their offspring had increased development time and lower development success 

after parental exposure to heat stress (Ismaeil et al. 2013). One possible mechanism may be heat 

stress damaging the quality of sperm both in males and in inseminated females, which can reduce 

fertility of the generation experiencing the heat waves as found in Tribolium castaneum Herbst 

(Coleoptera: Tenebrionidae) (Sales et al. 2019). In T. castaneum, the fecundity and lifespan of 

offspring produced by sperm that was exposed to heat waves was also reduced (Sales et al. 

2019).  

 

We simulated heat waves around the highest temperature (40.5˚C) measured within the 

past five years in Michigan. Temperatures used in the lower range of our heat wave treatments 

can already be experienced in the region, while the higher ranges may be reached within a few 

decades if current trends continue. Contrary to expectations, we found that our treatments 

affected the herbivore host, H. halys more severely than its egg parasitoid, Tr. japonicus. Heat 

waves can directly impact both trophic levels but for Tr. japonicus the negative effects became 

only apparent at higher temperatures than for H. halys. Clearly, our experiments have limitations 

as they took place in an artificial environment where neither the host nor the parasitoids could 

exhibit behaviors that may mediate the impact of heat stress. Nevertheless, our findings highlight 

the diversity of responses different life stages of a species may have to intermittent heat stress 

and underscore the importance of following populations beyond the first generation when 

evaluating the effects of heat waves.

 

55 

 

 

 

 

 

 

 

 

 

 

 

 

 

 
 

 

REFERENCES 

 

 

 

 

 

 

 

 

56 

REFERENCES 

 

 
 
Abram, P. K., K. A. Hoelmer, A. Acebes-Doria, H. Andrews, E. H. Beers, J. C. Bergh, R. 

Bessin, D. Biddinger, P. Botch, M. L. Buffington, M. L. Cornelius, E. Costi, E. S. Delfosse, 
C. Dieckhoff, R. Dobson, Z. Donais, M. Grieshop, G. Hamilton, T. Haye, C. Hedstrom, M. 
V. Herlihy, M. S. Hoddle, C. R. R. Hooks, P. Jentsch, N. K. Joshi, T. P. Kuhar, J. Lara, J. 
C. Lee, A. Legrand, T. C. Leskey, D. Lowenstein, L. Maistrello, C. R. Mathews, J. M. 
Milnes, W. R. Morrison, A. L. Nielsen, E. C. Ogburn, C. H. Pickett, K. Poley, J. Pote, J. 
Radl, P. M. Shrewsbury, E. Talamas, L. Tavella, J. F. Walgenbach, R. Waterworth, D. C. 
Weber, C. Welty, and N. G. Wiman. 2017. Indigenous arthropod natural enemies of the 
invasive brown marmorated stink bug in North America and Europe. Journal of Pest 
Science. 90, 1009–1020. 

 
Abram, P. K., N. J. Mills, and E. H. Beers. 2020. Classical biological control of invasive stink 

bugs with egg parasitoids – what does success look like? Pest Management Science. 6, 
1980-1992. 

Aguilar‐Fenollosa, E., Jacas, J.A., 2014. Can we forecast the effects of climate change on 

entomophagous biological control agents? Pest Management Science. 70, 853-859. 

Angilletta Jr, M.J., Niewiarowski, P.H., Navas, C.A., 2002. The evolution of thermal physiology 

in ectotherms. Journal of Thermal Biology. 27, 249-268. 

Avila, G. and Charles, J. 2018. Modelling the potential geographic distribution of Trissolcus 
japonicus: a biological control agent of the brown marmorated stink bug, Halyomorpha 
halys. BioControl. 63, 505-518. 

 
Baek, S., Y. Son, and Y.-L. Park. 2014. Temperature-dependent development and survival of 

Podisus maculiventris (Hemiptera: Pentatomidae): implications for mass rearing and 
biological control. Journal of Pest Science. 87, 331–340. 

Bale, J.S., Masters, G.J., Hodkinson, I.D., Awmack, C., Bezemer, T.M., Brown, V.K., 

Butterfield, J., Buse, A., Coulson, J.C., Farrar, J., 2002. Herbivory in global climate 
change research: direct effects of rising temperature on insect herbivores. Global Change 
Biology. 8, 1-16. 

Bannerman, J.A., Gillespie, D.R., Roitberg, B.D., 2011. The impacts of extreme and fluctuating 

temperatures on trait‐mediated indirect aphid–parasitoid interactions. Ecological 
Entomology. 36, 490-498. 

 
Blackburn, T.M., Lockwood, J.L. & Cassey, P. 2015. The influence of numbers on invasion 

success. Molecular Ecology. 24, 1942–1953. 

 
Borowiec, N., Thaon, M., Brancaccio, L., Cailleret, B., Ris, N., Vercken, E., 2018. Early 

population dynamics in classical biological control: establishment of the exotic parasitoid 

 

57 

Torymus sinensis and control of its target pest, the chestnut gall wasp Dryocosmus 
kuriphilus, in France. Entomologia Experimentalis et Applicata. 166, 367-379. 

 
Botch, P.S. and Delfosse, E.S. 2018. Host-Acceptance Behavior of Trissolcus japonicus 

(Hymenoptera: Scelionidae) Reared on the Invasive Halyomorpha halys (Heteroptera: 
Pentatomidae) and Nontarget Species. Environmental Entomology. 47, 403-411.  

Botch, P.S., Delfosse, E.S., 2018. Host-acceptance behavior of Trissolcus japonicus 

(Hymenoptera: Scelionidae) reared on the invasive Halyomorpha halys (Heteroptera: 
Pentatomidae) and nontarget species. Environmental Entomology. 47, 403-411. 

Bowler, K., Terblanche, J.S., 2008. Insect thermal tolerance: what is the role of ontogeny, ageing 

and senescence? Biological Reviews. 83, 339-355. 

Chiu, M.C., Kuo Jr, J., Kuo, M.H., 2015. Life stage‐dependent effects of experimental heat 

waves on an insect herbivore. Ecological Entomology. 2, 175-181. 

Chown, S.L., Terblanche, J.S., 2006. Physiological diversity in insects: ecological and 

evolutionary contexts. Advances in Insect Physiology. 33, 50-152. 

 
Cock, M.J., Murphy, S.T., Kairo, M.T., Thompson, E., Murphy, R.J., Francis, A.W., 2016. 

Trends in the classical biological control of insect pests by insects: an update of the 
BIOCAT database. BioControl. 61, 349-363. 

 
Cornelius, M. L., C. Dieckhoff, K. A. Hoelmer, R. T. Olsen, D. C. Weber, M. V. Herlihy, E. J. 
Talamas, B. T. Vinyard, and M. H. Greenstone. 2016. Biological control of sentinel egg 
masses of the exotic invasive stink bug Halyomorpha halys (Stål) in Mid-Atlantic USA 
ornamental landscapes. Biological Control. 103, 11–20. 

 
Cornelius, M.L., Dieckhoff, C., Vinyard, B.T., Hoelmer, K.A., 2016. Parasitism and predation on 
sentinel egg masses of the brown marmorated stink bug (Hemiptera: Pentatomidae) in three 
vegetable crops: importance of dissections for evaluating the impact of native parasitoids 
on an exotic pest. Environmental Entomology.134. 

 
Courchamp, F., Berec, L., Gascoigne, J., 2008. Allee effects in ecology and conservation. Oxford        

University Press. 

De Boeck, H.J., Dreesen, F.E., Janssens, I.A., Nijs, I., 2010. Climatic characteristics of heat 

waves and their simulation in plant experiments. Global Change Biology. 16, 1992-2000. 

Deutsch, C.A., Tewksbury, J.J., Huey, R.B., Sheldon, K.S., Ghalambor, C.K., Haak, D.C., 

Martin, P.R., 2008. Impacts of climate warming on terrestrial ectotherms across latitude. 
Proceedings of the National Academy of Sciences. 105, 6668-6672. 

Dieckhoff C, Tatman K.M, and Hoelmer K.A. 2017 Natural biological control of Halyomorpha 

halys by native egg parasitoids: a multi-year survey in northern Delaware. Journal of Pest 
Science. 1-16.  

 

58 

Ebi, K.L., Meehl, G.A., 2007. The heat is on: climate change and heatwaves in the Midwest. 

Regional impacts of climate change: four case studies in the United States, 8-21. 

Faúndez, E.I., Rider, D.A., 2017. The brown marmorated stink bug Halyomorpha halys (Stål, 

1855)(Heteroptera: Pentatomidae) in Chile. Arquivos Entomolóxicos. 305-307. 

Fauvergue X and Hopper KR. 2009. French wasps in the New World: experimental biological 

control introductions reveal a demographic Allee effect. Population Ecology. 51, 385-397. 

 
Fauvergue X, Malausa J-C, Giuge L and Courchamp F. 2007. Invading parasitoids suffer no 

Allee effect: a manipulative field experiment. Ecology. 88: 2392-2403. 

 
Fauvergue, X., Vercken, E., Malausa, T., Hufbauer, R.A., 2012. The biology of small, introduced 
populations, with special reference to biological control. Evolutionary Applications. 5, 424-
443. 

Fellowes, M., Kraaijeveld, A., Godfray, H., 1999. Cross‐resistance following artificial selection 
for increased defense against parasitoids in Drosophila melanogaster. Evolution. 53, 966-
972. 

Foden, W., Mace, G., Vié, J.-C., Angulo, A., Butchart, S., DeVantier, L., Dublin, H., Gutsche, 

A., Stuart, S., Turak, E., 2008. Species susceptibility to climate change impacts. Wildlife 
in a Changing World. 77-88. 

Gariepy, T.D., Talamas, E.J., 2019. Discovery of Trissolcus japonicus (Hymenoptera: 

Scelionidae) in Ontario, Canada. The Canadian Entomologist. 151, 824-826. 

Gillespie, D.R., Nasreen, A., Moffat, C.E., Clarke, P., Roitberg, B.D., 2012. Effects of simulated 
heat waves on an experimental community of pepper plants, green peach aphids and two 
parasitoid species. Oikos. 121, 149-159. 

Grevstad, F., Coombs, E. and McEvoy, P. 2011. Revisiting release strategies in biological 
control of weeds: are we using enough releases: Proceedings of the XIII International 
Symposium on Biological Control of Weeds. 368-376. 

 
Grevstad, F.S. 1999a. Factors influencing the chance of population establishment: implications 

for release strategies in biocontrol. Ecological Applications. 9, 1439-1447. 

 
Grevstad, F.S. 1999b. Experimental invasions using biological control introductions: the 

influence of release size on the chance of population establishment. Biological Invasions. 1, 
313-323. 

 
Grevstad, F.S. 2006. Ten-year impacts of the biological control agents Galerucella pusilla and 
G. calmariensis (Coleoptera: Chrysomelidae) on purple loosestrife (Lythrum salicaria) in 
Central New York State. Biological Control. 39, 1-8. 

Hance, T., van Baaren, J., Vernon, P., Boivin, G., 2007. Impact of extreme temperatures on 

parasitoids in a climate change perspective. Annu. Rev. Entomol. 52, 107-126. 

 

59 

Haye, T., Abdallah, S., Gariepy, T., Wyniger, D., 2014. Phenology, life table analysis and 

temperature requirements of the invasive brown marmorated stink bug, Halyomorpha 
halys, in Europe. Journal of Pest Science. 87, 407-418. 

Haye, T., Fischer, S., Zhang, J., Gariepy, T., 2015. Can native egg parasitoids adopt the invasive 

brown marmorated stink bug, Halyomorpha halys (Heteroptera: Pentatomidae), in 
Europe? Journal of Pest Science. 88, 693-705. 

 Haye, T., Moraglio, S.T., Stahl, J., Visentin, S., Gregorio, T., Tavella, L., 2020. Fundamental 

host range of Trissolcus japonicus in Europe. Journal of Pest Science. 93, 171-182. 

Hedge, L.H., O'Connor, W.A. and Johnston, E.L. 2012. Manipulating the intrinsic parameters of 

propagule pressure: implications for bio‐invasion. Ecosphere. 3, 1-13. 

 
Hedstrom, C., Lowenstein, D., Andrews, H., Bai, B., Wiman, N., 2017. Pentatomid host 

suitability and the discovery of introduced populations of Trissolcus japonicus in Oregon. 
Journal of Pest Science. 90, 1169-1179.  

Hegazi, E., Khafagi, W., 2005. Developmental interaction between suboptimal instars of 

Spodoptera littoralis (Lepidoptera: Noctuidae) and its parasitoid Microplitis rufiventris 
(Hymenoptera: Braconidae). Archives of Insect Biochemistry and Physiology: Published 
in Collaboration with the Entomological Society of America. 60, 172-184. 

Herlihy, M.V, Talamas, E.J, and Weber, D.C. 2016. Attack and success of native and exotic 

parasitoids on eggs of Halyomorpha halys in three Maryland habitats. PloS one. 
11(3):e0150275. 

Hickling, R., Roy, D.B., Hill, J.K., Fox, R., Thomas, C.D., 2006. The distributions of a wide 
range of taxonomic groups are expanding polewards. Global change biology. 12, 450-
455. 

Hoebeke, E.R., Carter, M.E., 2003. Halyomorpha halys (Stǻl) (Heteroptera: Pentatomidae): a 
polyphagous plant pest from Asia newly detected in North America. Proceedings of the 
Entomological Society of Washington. 105, 225-237. 

 
Hopper, K.R. and Roush, R.T. 1993. Mate finding, dispersal, number released, and the success of 

biological control introductions. Ecological entomology. 18, 321-331. 

Houghton, J., 2009. Global warming: the complete briefing. Cambridge university press. 

Hufbauer, R., Rutschmann, A., Serrate, B., de Conchard, H.V., Facon, B., 2013. Role of 

propagule pressure in colonization success: disentangling the relative importance of 
demographic, genetic and habitat effects. Journal of Evolutionary Biology. 26, 1691-1699. 

 
Ismaeil, I., Doury, G., Desouhant, E., Dubois, F., Prevost, G., Couty, A., 2013. Trans-

generational effects of mild heat stress on the life history traits of an aphid parasitoid. 
PLoS One. 8, e54306. 

 

60 

Jarrett, B. J. M., J. Pote, E. Talamas, L. Gut, M. Szűcs. 2019. The discovery of Trissolcus 
japonicus (Hymenoptera: Scelionidae) in Michigan. The Great Lakes Entomologist. 

JMP Pro, Version 13. 2016. SAS Institute Inc., Cary, NC, 1989-2019. 

Jones, A. L., D. E. Jennings, C. R. R. Hooks, and P. M. Shrewsbury. 2014. Sentinel eggs 

underestimate rates of parasitism of the exotic brown marmorated stink bug, Halyomorpha 
halys. Biological Control. 78, 61–66. 

 
Jones, A.L., Jennings, D.E., Hooks, C.R., Shrewsbury, P.M., 2017. Field surveys of egg 

mortality and indigenous egg parasitoids of the brown marmorated stink bug, Halyomorpha 
halys, in ornamental nurseries in the mid-Atlantic region of the USA. Journal of pest 
science. 90, 1159-1168. 

 
Kaser, A. J. M., C. Akotsen-mensah, E. J. Talamas, and A. L. Nielsen. 2019. First Report of 
Trissolcus japonicus Parasitizing Halyomorpha halys in North American Agriculture. 
Florida Entomol. 101, 680–683. 

Kingsolver, J.G., Arthur Woods, H., Buckley, L.B., Potter, K.A., MacLean, H.J., Higgins, J.K., 

2011. Complex life cycles and the responses of insects to climate change. Oxford 
University Press. 

Klockmann, M., Günter, F., Fischer, K., 2017. Heat resistance throughout ontogeny: body size 

constrains thermal tolerance. Global change biology. 23, 686-696. 

Koontz, M.J, Oldfather, M.F, Melbourne, B.A and Hufbauer, R.A. 2018. Parsing propagule 

pressure: Number, not size, of introductions drives colonization success in a novel 
environment. Ecology and Evolution. 8, 8043-8054. 

 
Lande, R., 1988. Genetics and demography in biological conservation. Science. 241, 1455-1460. 
 
Lande, R., 1993. Risks of population extinction from demographic and environmental 

stochasticity and random catastrophes. The American Naturalist 142, 911-927. 

 
Lande, R., 1998. Demographic stochasticity and Allee effect on a scale with isotropic noise. 

Oikos, 353-358. 

Lee, D.H., Short, B.D., Joseph, S.V., Bergh, J.C., Leskey, T.C., 2013. Review of the biology, 
ecology, and management of Halyomorpha halys (Hemiptera: Pentatomidae) in China, 
Japan, and the Republic of Korea. Environmental Entomology. 42, 627-641. 

Legaspi, J. C. 2004. Life History of Podisus maculiventris (Heteroptera: Pentatomidae) Adult 
Females Under Different Constant Temperatures. Environmental Entomology. 33, 1200–
1206. 

 
Leskey, T. C., B. D. Short, B. R. Butler, and S. E. Wright. 2012b. Impact of the invasive brown 
marmorated stink bug, Halyomorpha halys (Stål), in mid-atlantic tree fruit orchards in the 
United States: case studies of commercial management. Psyche. 201, 1–14. 

 

61 

Leskey, T. C., G. C. Hamilton, A. L. Nielsen, D. F. Polk, C. Rodriguez-Saona, J. C. Bergh, D. A. 

Herbert, T. P. Kuhar, D. Pfeiffer, G. P. Dively, C. R. R. Hooks, M. J. Raupp, P. M. 
Shrewsbury, G. Krawczyk, P. W. Shearer, J. Whalen, C. Koplinka-Loehr, E. Myers, D. 
Inkley, K. A. Hoelmer, D.-H. Lee, and S. E. Wright. 2012. Pest Status of the Brown 
Marmorated Stink Bug, Halyomorpha Halys in the USA. Outlooks on Pest Management. 
23, 218-226(9). 

Leskey, T.C., Nielsen, A.L., 2018. Impact of the invasive brown marmorated stink bug in North 

America and Europe: history, biology, ecology, and management. Annual Review of 
Entomology. 63, 599-618. 

Li Z-x, Y-s Liu. 2004. Effect of temperature on development of eggs parasitoid Trissolcus 

halyomorphae and the eggs of its host, Halyomonrpha halys. Chinese Journal of 
Biological Control. 20, 64–66. 

 
Lockwood, J.L., Cassey, P., Blackburn, T., 2005. The role of propagule pressure in explaining 

species invasions. Trends in Ecology and Evolution. 20, 223-228. 

 
Ma, C.-S., Ma, G., Pincebourde, S., 2020. Survive a warming climate: Insect responses to 

extreme high temperatures. Annual Review of Entomology. 66. 

Memmott, J., Craze, P., Harman, H., Syrett, P. and Fowler S. 2005. The effect of propagule size 

on the invasion of an alien insect. Journal of Animal Ecology. 74, 50-62. 

 
Memmott, J., Fowler, S. and Hill, R. 1998. The effect of release size on the probability of 

establishment of biological control agents: gorse thrips (Sericothrips staphylinus) released 
against gorse (Ulex europaeus) in New Zealand. Biocontrol Science and Technology. 8, 
103-115. 

 
Michigan Agricultural Statistics. 2017-2018. 

https://www.nass.usda.gov/Statistics_by_State/Michigan/Publications/Annual_Statistical_
Bulletin/stats18/agstat2018.pdf. 

 
Milnes, J.M, Wiman, N.G, Talamas, E.J, Brunner, J.F, Hoelmer, K.A, Buffington, M.L and 

Beers, E.H. 2016. Discovery of an exotic egg parasitoid of the brown marmorated stink 
bug, Halyomorpha halys (Stål) in the Pacific Northwest. Proceedings of the Entomological 
Society of Washington. 118, 466-471.  

 
Milnes, J.M., Beers, E.H., 2019. Trissolcus japonicus (Hymenoptera: Scelionidae) causes low 

levels of parasitism in three North American pentatomids under field conditions. Journal of 
Insect Science. 19, 15. 

Montserrat, M., Sahún, R.M., Guzmán, C., 2013. Can climate change jeopardize predator control 

of invasive herbivore species? A case study in avocado agro-ecosystems in Spain. 
Experimental and Applied Acarology. 59, 27-42. 

 

62 

Mousseau, T.A., Dingle, H., 1991. Maternal effects in insect life histories. Annual Review of 

Entomology. 36, 511-534. 

Nielsen, A. L., S. Chen, and S. J. Fleischer. 2016. Coupling Developmental Physiology, 
Photoperiod, and Temperature to Model Phenology and Dynamics of an Invasive 
Heteropteran, Halyomorpha halys. Frontiers of Physiology. 7. 

Nielsen, A.L., Fleischer, S., Hamilton, G.C., Hancock, T., Krawczyk, G., Lee, J.C., Ogburn, E., 

Pote, J.M., Raudenbush, A., and Rucker, A., 2017. Phenology of brown marmorated stink 
bug described using female reproductive development. Ecology and Evolution. 7, 6680-
6690. 

Ogburn, E. C., R. Bessin, C. Dieckhoff, R. Dobson, M. Grieshop, K. A. Hoelmer, C. Mathews, J. 

Moore, A. L. Nielsen, K. Poley, J. M. Pote, M. Rogers, C. Welty, and J. F. Walgenbach. 
2016. Natural enemy impact on eggs of the invasive brown marmorated stink bug, 
Halyomorpha halys (Stål) (Hemiptera: Pentatomidae), in organic agroecosystems: A 
regional assessment. Biological Control. 101. 

Parmesan, C., Ryrholm, N., Stefanescu, C., Hill, J.K., Thomas, C.D., Descimon, H., Huntley, B., 

Kaila, L., Kullberg, J., Tammaru, T., 1999. Poleward shifts in geographical ranges of 
butterfly species associated with regional warming. Nature. 399, 579-583. 

Pincebourde, S., Casas, J., 2015. Warming tolerance across insect ontogeny: influence of joint 

shifts in microclimates and thermal limits. Ecology. 96, 986-997. 

Qiu, L., Yang, Z., Tao, W. 2007. Biology and population dynamics of Trissolcus halyomorphae. 

Scientia Silvae Sinicae 43:62–65. 

 
Quinn, N. F., E. J. Talamas, A. L. Acebes-Doria, T. C. Leskey, and J. C. Bergh. 2019. Vertical 

Sampling in Tree Canopies for Halyomorpha halys (Hemiptera: Pentatomidae) Life Stages 
and its Egg Parasitoid, Trissolcus japonicus (Hymenoptera: Scelionidae). Environmental 
Entomology. 48, 173–180. 

 
R Core Team. 2019. R: A language and environment for statistical computing. R Foundation for 

Statistical Computing, Vienna, Austria. URL https://www.R-project.org/. 

Ratte, H.T., 1984. Temperature and insect development. Environmental physiology and 

biochemistry of insects. Springer. 33-66. 

Régnière, J., Powell, J., Bentz, B., Nealis, V., 2012. Effects of temperature on development, 

survival and reproduction of insects: experimental design, data analysis and modeling. 
Journal of Insect Physiology. 58, 634-647. 

Rice, K. B., C. J. Bergh, E. J. Bergmann, D. J. Biddinger, C. Dieckhoff, G. Dively, H. Fraser, T. 

Gariepy, G. Hamilton, T. Haye, A. Herbert, K. Hoelmer, C. R. Hooks, A. Jones, G. 
Krawczyk, T. Kuhar, H. Martinson, W. Mitchell, A. L. Nielsen, D. G. Pfeiffer, M. J. 
Raupp, C. Rodriguez-Saona, P. Shearer, P. Shrewsbury, P. D. Venugopal, J. Whalen, N. G. 

 

63 

Wiman, T. C. Leskey, and J. F. Tooker. 2014. Biology, Ecology, and Management of 
Brown Marmorated Stink Bug (Hemiptera: Pentatomidae). Journal of Integrated Pest 
Management. 5, 1–13. 

Roux, O., Le Lann, C., Van Alphen, J., Van Baaren, J., 2010. How does heat shock affect the life 

history traits of adults and progeny of the aphid parasitoid Aphidius avenae 
(Hymenoptera: Aphidiidae)? Bulletin of Entomological Research. 100, 543. 

Sales, K., Vasudeva, R., Dickinson, M.E., Godwin, J.L., Lumley, A.J., Michalczyk, Ł., 

Hebberecht, L., Thomas, P., Franco, A., Gage, M.J., 2018. Experimental heatwaves 
compromise sperm function and cause transgenerational damage in a model insect. 
Nature Communications. 9, 1-11. 

Schreven, S.J., Frago, E., Stens, A., De Jong, P.W., Van Loon, J.J., 2017. Contrasting effects of 
heat pulses on different trophic levels, an experiment with a herbivore-parasitoid model 
system. PLoS One. 12, e0176704. 

Sentis, A., Hemptinne, J.L., Brodeur, J., 2013. Effects of simulated heat waves on an 

experimental plant–herbivore–predator food chain. Global change biology. 19, 833-842. 

Shea, K. and Possingham, H.P. 2000. Optimal release strategies for biological control agents: an 

application of stochastic dynamic programming to population management. Journal of 
Applied Ecology. 37: 77-86.  

 
Simberloff, D., 2009. The role of propagule pressure in biological invasions. Annual Review of 

Ecology, Evolution, and Systematics. 40, 81-102. 

 
Sinclair, J.S. and Arnott, S.E. 2016. Strength in size not numbers: propagule size more important 

than number in sexually reproducing populations. Biological invasions. 18, 497-505. 

 
Skillman, V. P., and J. C. Lee. 2017. Nutrient Content of Brown Marmorated Stink Bug Eggs 

and Comparisons Between Experimental Uses. Journal of Insect Science 17. 

Stahl, J., Tortorici, F., Pontini, M., Bon, M.-C., Hoelmer, K., Marazzi, C., Tavella, L., Haye, T., 
2019. First discovery of adventive populations of Trissolcus japonicus in Europe. Journal 
of Pest Science. 92, 371-379. 

Szűcs, M., Melbourne, B.A., Tuff, T., Hufbauer, R.A., 2014. The roles of demography and 

genetics in the early stages of colonization. Proceedings of the Royal Society of London B: 
Biological Sciences. 281, 20141073. 

Szűcs, M., Melbourne, B.A., Tuff, T., Weiss‐Lehman, C., Hufbauer, R.A., 2017. Genetic and 

demographic founder effects have long‐term fitness consequences for colonising 
populations. Ecology letters. 20, 436-444. 

 
Talamas, E.J, Buffington, M., Hoelmer, K. 2013. New synonymy of Trissolcus halyomorphae 

Yang. Journal of Hymenopteran Research. 33,113–17  

 

64 

Talamas, E.J., Herlihy, M.V., Dieckhoff, C., Hoelmer, K.A., Buffington, M., Bon, M.-C., Weber, 

D.C., 2015. Trissolcus japonicus (Ashmead)(Hymenoptera, Scelionidae) emerges in 
North America. Journal of Hymenoptera Research. 43, 119. 

Voigt, W., Perner, J., Davis, A.J., Eggers, T., Schumacher, J., Bährmann, R., Fabian, B., 

Heinrich, W., Köhler, G., Lichter, D., 2003. Trophic levels are differentially sensitive to 
climate. Ecology. 84, 2444-2453. 

Wilson, J., Gut, L., Haas, M., Grieshop, M., Poley, K., Shane, W. 2018. Managing brown 

marmorated stink bug in Michigan orchards. Fact sheet 

Yang, S.Y., Zhan, H.X., Zhang, F., Babendreier, D., Zhong, Y.Z., Lou, Q.Z., Zhong, Y., Zhang, 

J.P., 2018. Development and fecundity of Trissolcus japonicus on fertilized and 
unfertilized eggs of the brown marmorated stink bug, Halyomorpha halys. Journal of Pest 
Science. 91, 1335-1343. 

Yang, Z.Q., Y.X. Yao, L.F. Qiu, and Z. X. Li. 2009. A New Species of Trissolcus 

(Hymenoptera: Scelionidae) Parasitizing Eggs of Halyomorpha halys (Heteroptera: 
Pentatomidae) in China with Comments on its Biology. Annals of the Entomological 
Society of America. 102: 39–47. 

 
Zhang, J., Zhang, F., Gariepy, T., Mason, P., Gillespie, D., Talamas, E. and Haye, T. 2017. 

Seasonal parasitism and host specificity of Trissolcus japonicus in northern China. Journal 
of pest science. 90, 1127-1141. 

Zhang, Y.B., Yang, A.P., Zhang, G.F., Liu, W.X., Wan, F.H., 2019. Effects of Simulated Heat 

Waves on Life History Traits of a Host Feeding Parasitoid. Insects. 10, 419. 

 

 

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