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II

 

FOOD AQUISITION BEHAVIOR OF PYCNOPSYCHE
GUTTIFER (LIMNEPHILIDAE: TRICHOPTERA)
PTERONARCYS PICTETTI (PTERONARCIDAE:

PLECOPTERA) AND ORCONECTES PROPINQUIS

(DECAPODA: causmcw. '

Thesis for the Degree of M. S.
MICHIGAN STATE UNIVERSITY
GAIL L, MOTYKA
1983

 

 

LIBRARY
I—fiichigan State
University

 

 

 

PLACE IN RETURN BOX to remove this checkout from your record.

TO AVOID FINES return on or before date due.
MAY BE RECALLED with earlier due date if requested.

 

DAIEDUE

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5/08 K:IPrq/Acc&Pres/CIRC/DateDue mdd

.<k \A;\
-3

AB STRA CT

FOOD AQUISITION BEHAVIOR OF PYCNOPSYCHE GUTTIFER (LIMNEPHILIDAE: TRICHOPTERA)
PTERONARCYS PICTETTI (PTERONARCIDAE: PLECOPTERA)
AND ORCONECTES PROPINQUIS (DECAPODA: CRUSTACEA).

 

 

 

By

Gail L. Motyka

Laboratory experiments were designed to discern whether two aquatic

detritivores Pycnopsyche guttifer and Pteronargs getetti are capable of using

 

 

chemical cues alone to find their food. These insects were given sterile and
microbially colonized leaf discs and allowed to feed for 2-4 days. Both _I_’_.
guttifer and E. pictetti fed significantly more on the microbially colonized leaf
discs. Flow through chamber experiments required the insects to find the more
acceptable leaf discs without contacting or seeing the discs. Behaviors were
quantified as average percent time spent per port. No significant differences
were found between time spent at stimulus ports (microbially colonized discs,
leaf extracts or fungal extracts) than at control ports (sterile discs or distilled

water respectively). Immature Oronectes propinquis were used as a positive

 

control since crayfish are known to respond to chemicals from food sources. 9.
propinquis spent significantly more time at stimulus (crayfish juice) than control
ports (distilled water). Preliminary experiments concerning the effects of light,

starvation periods, acclimation periods, and stimulus strength are discussed.

FOOD AQUISITION BEHAVIOR OF PYCNOPSYCHE GUTTIFER (LIMNEPHILIDAE: TRICHOPTERA)
PTERONARCYS PICTETTI (PTERONARCIDAE: PLECOPTERA)
AND ORCONECTES PROPINQUIS (DECAPODA: CRUSTACEA).

 

 

 

BY

Gail L. Motyka

A THESIS

Submitted to
Michigan State University
in partial fulfillment of the requirements
for the degree of

MASTER OF SCIENCE

Department of Entomology

1 983

To those who promote the quality of education.

ii

ACKNOWLEDGMENTS

Sincerest thanks to my advisor Rich Merritt and committee members Mike
Klug, Jim Miller, and Ed Grafius for unending support and encouragement.
Special thanks to Dan Lawson who guided me through dire straits. Essential to
by my progress were my office mates John Haefner, Bill Taft, and Kevin Webb.
Finally, my thanks to Susan Battenfield and Cathy Stewart for putting up with

continuous last minute demands for word processing expertise.

iii

TABLE OF CONTENTS

LIST OF TABLES .............................................. v
LIST OF FIGURES ............................................. vi
INTRODUCTION .............................................. 1
MATERIALS AND METHODS ................................... 7
Food Acceptability Experiments ............................. 8
Feeding Behavior .......................................... 9
Scanning Electron Microscopy ............................... 14
RESULTS .................................................... 14
Food Acceptability ........................................ 14
Feeding Behavior .......................................... 14
Scanning Electron Microscopy ............................... 19
DISCUSSION .................................................. 19
Scanning Electron Microscopy ............................... 29
REFERENCES ................................................ 32
APPENDIX I ................................................. 38

iv

i.

ii.

iii.

iv.

LIST OF TABLES

Synopsis of food acceptability experiments. .......................
Flow-through chamber behavioral experiments. ....................
Results of food acceptability experiments. ........................
Results of static water arena experiments with Q. propingui . .. ......

Results of flow-through chamber behavioral experiments. ...........

13

13

18

18

1.

3a.

3b.

4a.

4b.

5a.

5b.

6a.

6b.

8.

10.
11.
12..
13.

14.

15.

LIST OF FIGURES

Plexiglas static water chamber. ...............................

Plexiglas flow-through chamber. ..............................

A typical path of movement for g. pseudolimnaeus in the

 

static water chamber. .......................................

A typical path of movement for _13. guttifer in the static

water chamber. ............................... . . . . . . . .......

A typical path of movement for _C_). propinquis in the static

water chamber with stimulus. .................................

A typical path of movement for Q. propinquis in the static

water chamber with stimulus. .................................

Sensilla of one segment of antenna. ............................

Oblique view of antenna showing arrangement of sensilla at

upper edge of each antennal segment. ..........................
Top view of antennal uniporous sensilla. ........................
Side view of antennal uniporous sensilla. .......................
Grouped sensilla of antenna. ..................................
Mouthparts, general view. ....................................
Sculptured uniporous sensilla. .................................
Socketed receptors of paraglossa. .............................
Cuticular plates and campaniform sensilla of paraglossa. .........
Head and mouth. ...........................................

Sensilla of mouthparts. ......................................

General relationship between environmental parameters and
the microdistribution of a species of benthic stream

macroinvertebrate (Cummins and Lauff 1969). ..................

Genetic and environmental influences on microhabitat

selection by Pych0psyche larvae (Cummins 1964). ...............

 

vi

10

12

15

15

17

17

21

21

21

21

23

23

23

23

25

25

25

28

28

INTRODUCTION

Deciduous woodland stream ecosystems rely primarily on autumnal leaf
input as an energy base (Hynes 1970, Hall 1971, Fisher & Likens 1973, Cummins
1974). Before man's alteration of the environment, most streams were heavily
shaded by riparian vegetation, favoring the evolution of communities capable of
subsisting on allochthonous input (Hynes 1963).

Autumn shed leaves undergo a series of biological and abiological trans-
formations after entering a stream; as a result, the leaves are more readily
eaten (or more acceptable, see Miller & Strickler (1983) for definition of
behavioral terms) and nutritious to benthic invertebrates (Barlocher & Kendrick
1981, Cummins 8: Klug 1979). After the initial leaching of the leaf, a succession
of bacteria and fungi colonize and gradually decompose the leaf. The microbes
are presumed to be nutritionally important since most detritivores are unable to
survive on uncolonized leaves (Kostalos & Seymour 1976, Kaushik & Hynes 1971,
Rossi & Fano 1979). This inability to survive might be attributed to benthic
invertebrates' lack of digestive enzymes effective in the degradation of
structural carbohydrates (Monk 1977).

Few aquatic invertebrates have been found to produce enzymes active
against native crystalline cellulose; however, all could degrade basic subunits of
cellulose such as cellobiose (Monk 1977, Bjarnov 1972, Kristensen 1972).
Barlocher (1982) proposed that fungal enzymes capable of degrading recalcitrant
substances such as cellulose, may supply subunits of these compounds which are
readily degraded by invertebrate enzymes, allowing assimilation of otherwise
undigestable leaf compounds. Thus, the extent of colonization by microbes would

control the availability of assimilable compounds.

Several laboratory studies have correlated leaf species and the degree of
microbial colonization of leaf litter with food acceptance by selected shredders
(detritivores that feed on coarse particulate organic matter) (Table 1).

Also leaf species without microflora, have been ranked according to their
acceptability to various shredders. Kaushik and Hynes (1971) offered elm,
maple, alder, oak and beech leaves to the amphipods, Hyallela, Gammarus and
the isopod, Asellus (an isopod). Elm was the most acceptable species and was
subsequently omitted from the next preference experiment. This procedure was
repeated until an ordered array of leaf acceptabilities was completed. Wallace
et al (1970) presented 3 sets of 5 different species of leaves to PeltOperla maria
NEEDHAM and SMITH (Plecoptera) and recorded the amount of leaf material
eaten. Alder, dogwood, sourwood and elm were the most acceptable species
(Table 1). Unfortunately, these investigations did not consider the fungal
biomass which probably varied over the range of species used. The tested
invertebrates may have been responding to differences in biomass and not to
chemical or physical differences in the ftmgal species.

Other investigations concerned shredder acceptance of leaves colonized
with variable amounts or types of microbiota. Kostalos and Seymour (1976)
treated leaves with antibiotics to discriminate between the effects of bacteria

and the effects of fungi on leaf acceptability. Gammarus minus SAY (Amphi-

 

poda) consumed more fungus enriched leaves and microbially colonized leaves
with reduced bacteria than leaves with a natural milieu of microbes. In a
subsequent test, _q. m spent much more time feeding on naturally colonized
leaves than sterile or bacteria enriched leaves. Kaushik and Hynes (1971)

allowed 9_. lacustris limnaeus SMITH to feed on autoclaved, antibiotic treated,

 

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4

and microbially colonized leaves. The colonized leaves were most acceptable,
but the meaning of this result was unclear since the effect of autoclaving and
antibiotic treatment on the leaves was unknown. In order to avoid these
complications, they set up an acceptability experiment using leaves grown
without nutrients at 10°C and leaves supplemented with nitrogen and
phosphorous at 20-220C. Nitrogen-and phosphorous-enriched leaves were most
acceptable since they sustained more abundant microflora relative to the
unenriched leaves. Another study related the degree of colonization to leaf
consumption by comparing leaves incubated on the surface of the stream bottom
and leaves buried in the stream substrate (Herbst 1980). Surface incubated
leaves were more acceptable than buried leaves since they decompose much
more rapidly and therefore supported a greater papulation of microbes than did
the buried leaves. Other investigators found that shredders fed upon microbially
colonized leaves more than sterile or uncolonized leaves (Kostalos & Seymour
1976, Mackay 8: Kalff 1973, Kaushik & Hynes 1971, Herbst 1980). Barlocher and
Kendrick (1973) reduced the question further by testing fungal species. They
presented 11 ash leaf discs, each inoculated with a different fungal species, and
one sterile control disc to 10 Gammarus which fed on the discs for one day. Leaf
discs colonized at 17°C by terrestrial hyphomycetes were more acceptable than
those with aquatic hyphomycetes; although, when discs were inoculated and incu-
bated at 0°C, the results were reversed. They concluded that different fungal
species affect feeding differentially. All tested shredders were somehow able to
distinguish between the different food substrates. None of the studies suggested
any behavioral mechanism for the detection of differences between leaves and

their state of colonization. Barlocher and Kendrick (1973) suggested that some

chemical or physical differences may exist between leaves which directs their
preferential feeding habits.

It is plausible that compounds released from leaves during decomposition
could act as cues, leading shredders to microbially colonized leaves. Suberkropp
et al (1976) followed the loss of soluble reducing sugars, polyphenols, hemicellu-
lose, lignin, lipid, and nitrogen from leaves during decomposition in a stream.
They later demonstrated differential enzyme activity and microbial biomass
during leaf decomposition (Suberkropp & Klug 1979).

Electrophysiological and behavioral studies have demonstrated the olfac-
tory and gustatory capabilities of numerous aquatic organisms. Lobsters have
aesthetascs (typical decapod chemosensilla) on their antennules which ftmction
primarily as olfactory chemosensilla while receptors on mouthparts respond
largely to gustatory stimuli. The aesthetascs of spiny and clawed lobsters are
highly sensitive to amino acids, particularly taurine, but are much less responsive
to proteins, carbohydrates and fatty acids (Phillips et a1 1980). Food finding
behavior in crabs can be elicited by stimulating the unbranched antenullar
aesthetascs with fish juice (Warner 1977). The fishjuice concentration had to be
significantly increased to invoke grasping behavior during simultaneous squirtings
of juice on dactyli and touching of dactyli with a glass rod. The inner flagellum
and dactyls of blinded crayfish Cambarus bartoni sciotensis RHOADES, exhibited
changes in spike potential when stimulated by glutamic acid (Hodgson 1958).
Also, a typical series of feeding behaviors was exhibited by the crayfish when

presented with muscle extracts. Planktonic shrimp, Acetes sibogag australis

 

COLEFAX are able to follow scent trails of food or paper soaked in meat

extract, (L-alanine, L-leucine, and L-methionine) (Hamner & Hamner 1976). In

the event of crossing a trail, the shrimp either move in rapid horizontal circular
paths along the trail, or sharply reorient the body axis to the trail and follow it
at three times their normal speed. Rittschof (1980) fomd that the flesh
consum ers Fundulus similis, Callinectes sapidus RATHBUN (blue crab), and

Melongena corona GMELIN (predatory gastropod), were attracted to small

 

molecules from the flesh of bivalves, gastropods and crabs, while shell users

Clibanarius vittatus (Bose) and Paggus longicarmg SAY (hermit crabs) were only

 

attracted to small molecules from gastropods. Mosquito larvae Culex pipiens

quinquefasciatus SAY respond to gradients of RNA and particular nucleoside

 

monophosphates in an aquarium by congregating in regions of high concentration
(Barber et al 1982). Chemotaxis was concluded to be the behavioral mechanism
employed by the larvae; however, the actual movements of the larvae from
original release position to the area of chemical stimulus were never observed.
Ultrastructural characteristics of the receptors thought to be involved in
olfaction and gustation, have been described for various crustaceans and
numerous terrestrial insects (Slifer 1970) while few aquatic insects have been
studied (Pritchard 1965, Bassemir 8: Hansen 1981). Zacharuk (1980) recently
reviewed insect chemosensilla classification, presenting a simplified version of
Altner's (1977) system. Most sensilla are some type of hair or bristle-like
structures. The terms multiporous and uniporous chemosensilla crudely dis-
tinguish olfactory or non-contact chemosensilla from gustatory or contact
chemosensilla. Multiporous sensilla typically have thin cuticle (= 0.111 thick)
relative to that of the uniporous sensilla. The decapodan counterpart to the
multiporous sensilla is the aesthetasc, a long and extremely thin walled receptor

with no pores. The walls may be entirely or partially permeable to environment-

al compounds, a luxury aquatic animals can afford. The pores of terrestrial
insects allow contact with the external environment without risking dessication.
The primary objective of this study was to determine if shredders respond
to compounds released from the leaf matrix during decomposition and ultimately
use these compounds to find microbially colonized leaves. In support of this
objective, the ultrastructural characteristics of Pycnopchhe guttifer and

Pteronarcys pictetti were studied to determine if these insects actually possess

 

the apparatus necessary for olfactory chemoreception.

MATERIALS AND METHODS

Immatures of Pteronarchs Lictetti HAGEN were collected from the

 

Escanaba River, Dickinson Co., MI. Those of Pycnopsyche @ttifer WALKER,

Gammarus meudolimnaeus BOUSFIELD, and Orconectes propinquis GIRARD

 

were collected from from Augusta Creek and its tributaries, Kalamazoo Co.,

Michigan.

LEAF DISCS

Pignut hickory (Caryaya Llabra (Sargent)) and ash (Fraxinus pennsylavanica

 

 

Marsh)) leaves were collected in nets, as shed, and stored dry. Hickory leaves
were soaked in water, cut into discs, dried at 50°C, weighed, and sterilized by
treatment with ethylene oxide. Leaves for preference experiments were
confined in a screen container within an artificial stream containing natural
detritus and benthic organisms. Concurrently, sterile leaf discs were
asceptically transferred to flasks of autoclaved water and incubated in a 15°C

shaker bath; this treatment served as a sterile control.

Pure cultures of Tetracladium marchalianum deWILD were grown in 150 m1

 

of an autoclaved mineral medium containing 10mM KNO3, 2.5mM KHZPO4, 3mM

NaCl, lmM MgSO 01% yeast extract, and .5% glucose. The culture was

4’ °
incubated at 15°C in 500ml Erlenmeyer flasks on a reciprocating water bath

shaker for at least 3 weeks before use or until fungal colonies were 5-10mm in

diameter.

FOOD ACCEPTABILITY EXPERIMENTS

Experiments were performed to determine if _P. guttifer and _P_. pictetti
would feed more on microbially colonized leaves than on non-colonized leaves as
other shredders do (Barlocher & Kendrick 1973, Mackay et al 1977). The results
also helped to ascertain the propriety of the leaves chosen as food stimuli for
behavioral experiments.

Animals were placed in 300 ml pyrex dishes (10 cm diameter x 5cm high)
with step tread (no slip surface) affixed to the bottom to provide a consistent
friction surface for locomotion. Two #2 pins were glued, upside down, to the
bottom, and each dish was aerated by passing air through a hypodermic needle
rather than through an airstone which disturbs the animals with air bubbles.
Animals were starved for 2 days before introduction into a dish. Three
unconditioned leaf discs were placed on one pin and 3 conditioned leaf discs on
the other pin. 2. pictetti was allowed to feed for 2 days and P. guttifer was left
for 3-4 days as they are slower feeders. Ten replicates were rim for each
species.

Since it was imperative that all leaf disc tissue remain unchanged by

quantification methods, a leaf area meter was used to assess leaf loss by

comparing change in leaf area over time. Excess moisture was drawn from each
disc using a paper towel before it was placed in the area meter. Discs were
immediately rewetted and placed in the feeding dishes. After the appropriate
feeding period, was complete, leaf areas were again determined and % change

calculated.

FEEDING BEHAVIOR

Behavioral experiments were designed to discern whether shredders can
find palatable food substrates using non-contact chemical cues. Initially, tests
were run in a static water arena (Fig. 1) to facilitate comparison with other
behavioral studies (Fraenkel & Gunn 1963). Microbially colonized leaves were
placed carefully in the middle of the arena. After currents had dissipated, the
insects were introduced; their movements, time, and number of animals reaching
the leaves were quantified by video tape analyses. To determine if successful
contact with the stimulus was accidental, control tests were run using pieces of
plastic screen (similar in size to treatment leaves) in place of leaves.

Tests of response to extracts were also conducted in the static chamber.
Organisms were allowed to acclimate to the chamber for 15 minutes, after which
time, leaf or fungal extract, or crayfish water, was poured gently into the center
of the arena. Paths of movement were traced from the video screen and
analyzed to quantify the speed of movement and rate of turning using a
computer program (see Appendix 1) in conjunction with a Tektronix' digitizer.
These two variables plus the amount of time spent in center v.3. sides, and
unusual, behaviors, were compared with control experiments using water as a

stimulus.

10

Water 0010‘“

 

      
    

   
  

 

_-- :gifiiv.

 
 
 
 

  

 

 

 

Water is input at 10°C through the
reeevoir in order to maintain the upper behavioral arena water
temperature at 15°C .

static chamber.

Plexiglas

FIGURE 1.

11

A flow through chamber (Fig. 2) was used for further behavioral testing.
Individual _P. guttifer and P. pictetti were placed in this chamber which consisted
of 8 ports opening into a common center area with drain. Water was pumped
into a reservoir below the main arena level, up through uniform holes around the
outer rim, and finally in to the drain. A 5cm high piece of screen was placed
across the ports so that test animals could not enter the ports. Water for the
arena was pumped from a 15°C living stream tmit with a Teel' submersible
pump.

Test animals were allowed to acclimate in the center area for 15 minutes
on the average. After acclimation, stimulus and control were carefully placed in
randomly chosen ports without creating shadows or vibrations which might
disturb test animals. The chamber was kept in an undisturbed room with natural
light averaging 4-6 foot candles. Animal movements were videotaped using a
Sony 340 Betamax' video cassette recorder, and a Sony AVG-3450 black and
white video camera containing a Sony nuvicon' tube which can record at light
intensities as low as 2 foot candles. The Sony 323 VCR, used in conjunction with
a 303 Auto Search Control, facilitated tape analysis through its slow/fast motion
and time display features. Time spent in front of each port and unusual
behaviors were determined from taped sequences.

Conditioned leaves and extracts were used as stimuli in behavioral experi-
ments (Table 2). Extracts were made by macerating 3g of leaf or ftmgal
material in a tissue grinder with 50 ml of distilled water until homogenous. The
homogenate was then filtered through Whatman #4 qualitative filters. Crayfish
food stimulus (crayfish water) was prepared by cutting crayfish into pieces,

leaving the pieces in distilled water overnight, and filtering the water. Stimuli

12

I II ..

B. Arena - 30cm diameter x 5cm deep.

Reservoir - 30cm diameter X 6cm deep.

C. Arena center - 14cm diameter.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

FIGURE 2. Plexiglas flow through chamber. Water flow is in the direction
of the arrows. Extracts were introduced into individual ports

via burets and Teflon tubing.

13

TABLE 2. Flow through chamber behavioral experiments.

EXP. TREATMENT CONTROL

 

Pycnopsyche guttifer

 

l conditioned ash leaf discs sterile hickory leaf discs
2 Tetracladium marchalianum distilled water

extract
3 conditioned leaf extract distilled water

Pteronarcys pictetti
4 conditioned ash leaf discs sterile hickory leaf discs

Orconectes propinguis
5 crayfish water distilled water

 

TABLE 3. Results of food acceptability experiments.

 

2.351s: W
CONDITIONED swine

g, pictetti 79.68 * .91

g, guttifer 81.52* .85

 

' stimulus different from control at .,001 using t test of diffs. between means.

14

were introduced into the arena through a buret with a hypodermic needle
attached to the tip and l m of .01cm diameter Teflon tubing running from the
needle to the appropriate port (Fig. 2). The extra tubing permitted the

maintenance of a relatively constant flow rate of extract into the arena.

SCANNING ELECTRON MICROSCOPY

Heads, mouthparts and antennae of E. pictetti and _P_. guttifer were fixed in
4% glutaraldehyde and rinsed in .lM buffer, fixed in 1% 0504 JM buffer and
dehydrated in a graded ethanol series (25%-100%). Specimens were then critical

point dried, (with CO as the transitional fluid), mounted, coated, and examined

2
in a JEOL JSM-3S6 SEM.

RESULTS
FOOD ACCEPTABILITY
Both 2. pictetti and _P. guttifer fed almost exclusively on the conditioned
ash leaves. At the end of each feeding trial, only the veins of the ash leaves

remained, while sterile leaf discs were virtually untouched (Table 3).

FEEDING BEHAVIOR

In preliminary tests using the static chamber, the number of animals
contacting the stimulus and observed behaviors were the same for leaves and
control screens, except that the shredders did not remain on the screen.
Analysis of differences in the speed of movement and rate of turning in response

to fungal extracts was not informative for g. geudolimnaeus because its pattern

 

of locomotion was so erratic (Fig. 3a). Similar analyses of _P. guttifer and P.

15

 

 

 

 

 

 

 

_IL I I T F j I 1
0.0 5.0 tc.o 15.3 29.0 25.: so.c 35.0 40.0

FIGURE 3a. *A typical path of movement for E, pseudolimnaeus

 

in the static water chamber. Observation period ' 7 mins.

:3 ' . . .
O a . _ ' '
o ' _ .'
u) ' - . . . ~ '
7A 71

O

 

 

 

20.0
.4__..._J

15.0
1

 

 

 

 

O ' —r I I ”T 1’ I r 1
0-0 5-0 10-0 15-0 20-0 25.0 30-0 35-0 40-0

FIGURE 3b. *A typical path of movement for g, guttifer in the static

water chamber. Observation period = 12.5 minutes.

*A = start. 8 = end. Concentric circles represent the diffusion of stimulus from the
point of introduction over time. The path was traced from the monitor screen, reduced.
and digitized on a Tektronix tablet. The data points were then plotted and output uSing
the MSU SPOCS program.

l6

pictetti revealed no differences between treatment and control; these insects
spent the majority of their time along the edge of the arena (Fig. 3b). Control
experiments were conducted using the crayfish which is known to respond to
chemicals from food sources. In these experiments, _Q. propinguis spent
significantly more time in the center of the arena after introduction of crayfish
water (Fig. 4a and b, Table 4).

In the flow-through chamber _13. ggttifer, _P. pictetti and _Q. propinguis
exhibited thigmotaids since they walked consistently around the edge of the
screen which delimited the ports from the central arena (Fig. 2). This behavior
caused them to enter the flow from each port. Individuals rarely left the screen,
but when this occurred, they typically crossed through the center and returned to
the screen, or simply turned 1800 and began moving in the opposite direction. In
these experiments, there were no changes in the insects' behavior when entering
the stimulus plume, and the time spent per port was never significantly different
(Table 4). All t values were checked against larger values of a. in order to assure
detection of any possible differences (Table 5). The crayfish, _Q. ro in uis,
spent significantly more time at the stimulus port in response to crayfish extract
(Table 5). Feeding behaviors similar to those described for the crayfish

Procambarus clarkii (Girard) (Ameyaw-Akumfi 1977) were observed for Q.

 

propinguis when it entered the plume of the stimulus port. _Q. propinguis made
brief movements in various directions which resulted in the maintenance of its
original position. The mouthparts and chelate walking legs made scooping
movements toward the mouth as though grasping something and placing it in the
mouth. In addition, the chelate walking legs picked at the substrate and the first

enlarged chelae appeared to clean the first antennae periodically.

17

 

 

 

 

 

 

 

C3
\— 0"
N O 0
* A .
o I
u:— . . °
9 ' 3
O- . '
c? .
m s
B
‘3
a r r t I t 7
0'0 SIG [0-0 15.0 2°00 25.0 3000
FIGURE 4a. ‘A typical path of movement

1
35.0

. for Q. propinguis in the static water
chamber with stimulus.

o '."“"’“

 

15.0
1

10.0
I

 

 

 

 

 

 

\
I ’1 -I T 1
20-0 25-0 30-0 35-0 40-0
T::“=: 41 *A typical path of movement for Q. propingui: in the static water
.narsz. ul;ncut stimulus.
*A:

start, B = end.

Concentric circles represent the diffusion of stimulus from the
pOint of introduction over time.

7
40.0

18

TABLE 4. Results of static water arena experiments with Q, propinqgis.

 

 

TREATMENTS

BEHAVIOR CONTROL - NO STIM. (s time) STIMULUS“ time)
locomotion away 4.266 13.7
from arena edge
picking at
substrate with -— 4.S~
chelae
cleaning antenn. - 4.0

TABLE EL Results of flow through chamber behavioral experiments.

 

SPECIES # of TREATMENT STIMULUS CONTROL
REPLICATES

g, ggttifer 10 condit. ash leaves 14.13ns 14.67a

4 I. E extract 15.36113 15.12

S condit.leaf extract 15.3ans 16.40

E, pictetti 9 condit.ash leaves 13.70ns 14.74

2, propinquis 7 ‘ crayfish water 33.19* 10.91

 

he no significant difference between stimulus and control

* significantly different at -.001

19

SCANNING ELECTRON MICROSCOPY

Several structures similar to sensilla found in other animals, were observed
using SEM. The antennae of E. ictetti, have an orderly arrangement of sensilla
arctmd the upper edge of each antennal segment (Fig. 5). The short stout sensilla
are uniporous sensilla (Fig. 6). The long thin sensilla may be multiporous sensilla
or some type of mechanoreceptor (Fig. 5). Those of most interest are the
grouped sensilla which appear to be thin walled or multiporous sensilla (Fig. 7)
and are somewhat reminiscent of the decapod aesthetascs discussed earlier. The
head (Fig. 8) and antennal base have uniporous sculptured sensilla (Fig. 9)
scattered over the entire surface, while the glossae and palps have typical
socketed mechanoreceptors (Fig. 10). Peculiar plate-like cuticular areas and
campaniform sensilla (Fig. 11) were found on the paraglossae. The only apparent
sensilla on _P_. guttifer were tiny pegs on the head (Fig. 12), and contact

chemosensilla on mouthparts (Fig. 13).

DISCUSSION

Data from these experiments failed to show that non-contact chemical
stimuli significantly influenced the food finding behavior of aquatic detritivores.
Such results often imply deficiencies in experimental design or errors in
apparatus design. The suitability of the design and execution of these
behaviorial experiments was supported by the positive results from experiments
using the crayfish. _Q. propinguis was tested because it is known to use olfactory
chemoreception in finding its food and it is similar to our test insects in size and
locomotory capabilities. Crayfish did respond as expected; they spent more time

in the middle of the static water arena where crayfish water was introduced and

20

PTERONARCYS PICTETTI - SEM

 

FIGURE 5a.

FIGURE 5b.

FIGURE 6a.

FIGURE 6b.

Sensilla of one segment of antenna. X20000

Oblique View of antenna showing arrangement of sensilla at
upper edge of each antennal segment. X18000

Top View of antennal uniporous sensilla. X4400

Side view of antennal uniporous sensilla. X3200

 

22

PTERONARCYS PICTETTI - SEM

 

FIGURE 7. Grouped sensilla of antenna. Probably thin walled. X2000
FIGURE 8. Mouthparts, general view. X26
FIGURE 9. Sculptured uniporous sensilla. X2000

FIGURE 10. Socketed receptors of paraglossa. X2000

23

 

PTERONARCYS PICTE'I'I'I - SEM
FIGURE 11. Cuticular plates and campaniform sensilla of paraglossa. X3000

PYCNOPSYCHE GUTTIFER - SEM

FIGURE 12. Head and mouth. X60

FIGURE 13. Sensilla of mouthparts. X260

25

 

26

spent more time at stimulus than at control ports in the flow-through chamber
experiments. Thus, we believe that the general experimental design was appro-
priate. Numerous questions remained unanswered: 1) were the insects hungry; 2)
was the light affecting their behavior; 3) were insects given enough time to
acclimate properly to their new environment; and 4) was the stimulus strong
enough? To answer these questions, starvation periods of 0-10 days were tried
and penultimate instar nymphs and larvae were used as they are highly involved
in feeding. Flow-through and static chamber experiments were repeated in
complete darkness and insects were allowed acclimation periods of 0-60 minutes
and 1 day, to decrease the effects of the unnatural environment. Concentrations
of extracts were varied before experemental techniques were finalized. No
changes in behavior were apparent with any of these alterations in experimental
design.

It appears that E. pictetti and _P. guttifer find their food through random
movement without the information derived from non-contact chemostimuli.
Considering their environment, it may not be particularly advantageous for these
shredders to use a long distance chemical cueing mechanism since their life
cycle is synchronized with the yearly flux of organic matter. Reice (1981) found
that competition for food was relatively unimportant among stream benthos in
New Hope Creek even though species microhabitats, feeding habits, and body
sizes were similar. Another consideration is that many shredders are actually
opporttmists, switching to periphyton, macrophytes, or autochthonous detritus
when necessary (Minshall 1978, Hynes 1975, Anderson & Sedell 1979, Peckarsky
1980). Williams & Williams (1982) and Cummins (1964) supported this observa-

tion in their studies of _. guttifer. Guts of _. guttifer contained large

27

percentages of leaf fragments and algae; chiefly diatoms and several filamentous
forms. Unfortunately, these investigations did not consider the suitability of
diatoms and periphyton as food since the ability of the shredders to assimilate
them is unknown. Shredders may not require a special mechanism for food
finding if they are essentially opportunists that have large quantities of suitable
food available throughout their larval and nymphal growth periods. Crayfish, on
the other hand, are scavengers that take advantage of ephemeral and spatially
restricted food resources such as recently killed animals. Therefore, it is
advantageous for them to have effective mechanisms for locating these
resources.

The fact remains that many shredders do feed on certain leaves more than
others and are not randomly distributed on leaves in natural stream systems.
Shredders typically exhibit a clumped distribution since they are found in
detritus, a food resource which is clumped in distribution (Egglishaw 1964). They
may use taste or tactile cues to recognize appropriate food; although, in natural
stream systems, this clumped distribution could occur in response to stream
microhabitats rather than food. Interactions between current velocity, substrate
size and food availability affect the distribution of invertebrates in a stream
(Cummins & Lauff 1969) (Fig. 14). A specific heirarchical arrangement of these
factors exists for each species. In the case of P. uttifer, different instars have
different substrate size preferences depending upon the requirements of case
building, feeding, and pupation (Fig. 15). Generally, _13. guttifer inhabits slow
water areas of a stream, particularly stream margins, although no current
velocity preferences were found in laboratory studies (Cummins 1964).

Minshall and Minshall (1976) observed that small particle substrates (1.5cm)

accumulated more detritus and supported an abundance of invertebrates relative

SUBSTRATE ——————————————— —' FOOD SUBSTANCES "1
PARTICLE I '
sxzs _ |
I I '
. . I! |
l l I '
' ' MICRODISTRIBUTION . . I
l l : l '
V l ' V

CURRENT VELOCITY-—" --"- '--' --° -—- OTHER PHYSICAL * CHEMICAL I
PARAMETERS (3.6., 02. TEMP)

mmmw—O-e_c—A_-*O*a-Q—O~JH0‘0“.

---4> influence of environment On a benthic species which results in
~ recognition of microhabitat

-—- --4> interactions between components of the environment to which a given
benthic species interacts

-—--: -e- influence of a given benthic species on the microhabitat

FIGURE 14. General relationships between environmental parameters and the
microdistribution of a species of benthic stream macroinvertebrate.(Cummins
s Lauff 1969).

GENETI CONTROL

HABITAT HABITAT
SELECTION SELECTION
substrate cue ————————— -¢> food cue
CASE CASE CASE CASE
FORM MATERIALS HA RIALS RH
ENVIRONMENT

FIGURE 15. Genetic and environmental influences on microhabitat
selection by Pycnopsyche larvae (Cummins 1964).

29

to larger substrates (4.5-7cm). When similar amounts of detritus collected on

larger substrates, invertebrate colonization was then similar on both substrates.

Correlations between the amount of detritus and invertebrate numbers may have
been coincidental since the accumulation of detritus is the result of the
combined effects of current and substrate.

Other studies have shown substrate preferences when detritus was not a

confounding factor. Limnephilus rhombicus (Linnaeus) and Potam0phylax

 

 

rottmdipennis, both shredders, spent more time on pebbles than on sand and more
time on coarse pebbles than on crushed brick (Higler 1975). If shredders respond
to substrate differences as described by Higler, then chemical cues may be of
secondary importance or may supply additional feeding information at best.
Peckarsky (1980) found more shredders in cages with conditioned and
unconditioned coarse particulate organic matter than in control cages. The
animals located a food substrate typically considered unacceptable and not
conducive to proper growth. The large numbers of shredders in control and
unconditioned leaf cages suggest a random search mechanism. Once appropriate
or inappropriate food is encountered, the decision can be made whether or not to

move to another area.

SCANNING ELECTRON MICROSCOPY

The purpose of studying the morphology of E. pictetti and _13. guttifer was
to document the potential chemosensory apparatus available for facilitation of
food finding. _I_’. pictetti does have sensilla which morphologically appear to have
olfactory capabilities, but their effectiveness in this capacity is unknown.

It is believed that insects evolved as terrestrial organisms and only

secondarily invaded aquatic habitats (Boudreaux 1979, Ross 1967, Edmunds 1972);

30

thus, as one might expect, the sensilla of P. pictetti are structurally similar to
the sensilla of terrestrial insects. The degree of adaptation of these sensilla to
the aquatic environment is an intriguing question.

What characteristics exemplify aquatically adapted chemosensilla?
Ghiradella et al (1968b) identified distinct differences in structure between the

aesthetasc hairs of Coenobita compressus, a terrestrial hermit crab, and Pagurus

 

hirsutiusculus (Dana) an aquatic hermit crab (Ghiradella et al 1968b). They
related the divergence in sensilla morphology to the "newly" aquired terrestrial
habits of Coenobita.

Several characters of Coenobita sensilla are convergent with terrestrial
insects while typical aquatic decapod characteristics are also present. Differ-
ences relate primarily to the problem of water conservation, encountered in the
switch from aquatic to terrestrial life. Both terrestrial insects and Coenobita
have blunt pegs which expose less surface area to evaporation. The ciliary
apparatus is set below the surface of the flagellum, effectively isolating all
structures except receptor elements of the cells from the permeable surface.
Vacuoles are found throughout the flagellum which insure a supply of moisture to
cilia and more distal elements. Aquatic decapods such as Paggrus have com-
pletely permeable flagella (Snow 1974, Ghiradella et al 1968b). Terrestrial
insect olfactory sensilla are not permeable to most compounds but have pores
which connect to the outside and liquor bathing the dendrites, thereby preventing
dessication of the sensilla. Coenobita aesthetascs are intermediate in form in
that only one side is permeable.

In addition to water conservation, there are problems of structural support.

Short stout pegs of terrestrial insects and Coenobita can maintain their integrity

31

without additional support, whereas long thin aesthetascs of aquatic decapods
require the pressure of an aquatic medium to prevent folding and matting of the
sensilla.

B. pictetti sensilla (50um x lOum) are proportional to the reduced
Coenobita aesthetascs (100nm x 20um). Pagurus aesthetascs are 200-1400um in
length and only 18-25um in diameter (Snow 1974). They typically occur in
populations of 400-600/outer flagellum and are densely packed. Thin walled
sensilla of E. pictetti are sparsely distributed on the antennae relative to
Pagurus and terrestrial insects in which olfaction is important such as
Hymenoptera (Agren 1978) and Lepidoptera (Slifer 1979).

In conclusion, the evidence presented here, supported by evolutionary and
ecological studies, suggests that these shredders do not use long distance
chemical cues to facilitate food finding. They may drift in the stream current
and settle out in pools with relatively fine particle organic matter, or become
snagged in rocks and other stream debris along with leaves. The chemosensory
apparati do not seem appropriate for effective long distance cuing in aquatic
habitats since the sensilla generally resemble those of terrestrial arthropods in
structure and are sparsely distributed. Electrophysiological and TEM studies of
the sensilla must be done before any firm conclusions can be made concerning

their function.

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PRCISRAM OUNOUI‘PUIHTAELTAPEZ.TW.TAPE3=GH‘PUP.TAPFI5l

RFWTND 1
RFWTND 3
RMND 2
RIC-WIND 5
W
I=fl

SDANG=fl
READ(1.50)X1.Y1
READ! 1 . 50)){2 .Y2
AF(Xl-X2
B=(Yl-Y2l

F=( A* *2+B**2)
WORNF)

MRITE(5.51)S.RCUI‘

com-mus
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%

SDANG=Z
IF(I.GI'.0)GO TO 63
P=HYP+RC1JT

HY
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X1=X2

D=(Y1-Y7)

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R=(C**2+D**2)
SO=SORT(O)
SR=SORT(R)
IF(SR. LT. .MGO

T—=(A/S0l*(C/SR)+()B/SOl*(D/SRl

ANG=ACDS( Tl
DANG=ANG* 57 . 3

HYP=HYP+SR
WRITE”). 51)S.SR
A=C

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MIC HIIISAI STATE UNIVERSITY LIBRARIE

IIIII III

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303