Emerald ash borer (EAB), Agrilus planipennis (Fairmaire) (Coleoptera: Buprestidae) is one of the most destructive forest insect pests to be introduced into North America. Oobius agrili Zhang and Huang (Hymenoptera: Encyrtidae) is an EAB egg parasitoid native to northeastern China. EAB has spread to most of eastern North America and O. agrili has been released throughout most of this distribution. Both species now occur well beyond their endemic climatic ranges. Furthermore, photoperiod modulates O. agrili diapause. Therefore, host-parasitoid synchrony could be affected in novel climatic distributions. Studies were conducted to determine the O. agrili life stages that respond to photoperiod and the critical day length for diapause induction. Results demonstrated that photoperiod induced diapause is modulated in the developing larvae and critical day length for diapause induction is between 14.25 and 14.5 hours of day light. Next. a temperature driven multiple cohort rate summation model was developed to simulate the phenology of O. agrili and EAB. Critical day length was integrated into the model to predict interactions of photoperiod and temperature regimes on host-parasitoid synchrony. The model was validated with O agrili and EAB trapping from Michigan sites. Model predictions compared with trapping data demonstrated that O. agrili has primarily two generations per year in south central and northwestern Michigan, and O. agrili enters diapause before critical day length occurs in south central Michigan. According to simulations, spatiotemporal variation in temperature regimes does not affect O. agrili-EAB synchrony, with the exception of some northern locations. However, the effect of spatial variation in day length is still unclear and dependent on how O. agrili measures day length in the field. Finally, sampling methods, sample size and seasonal timing for detecting and monitoring O. agrili in the field were evaluated. Yellow pan traps and bark sifting for parasitized eggs were more effective at recovering O. agrili compared to sentinel EAB eggs in screened pouches and bark rearing for adults. A minimum of ten yellow pan trap or bark sifting samples should be taken from each site. Yellow pan trap sampling should be conducted between 400-1200 DD10. Results of this project provide insight and tools for evaluating O. agrili phenology and spatiotemporal synchrony with EAB oviposition, determining optimal release times, and detecting and monitoring its efficacy across its current and potential distribution in North America.
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