Microclimate affects emergence phenology without impacting the reproductive fitness of field-reared Oobius agrili (Hymenoptera: Encyrtidae): implications for classical biological control of emerald ash borer Agrilus planipennis Fairmaire (Coleoptera: Buprestidae)

The solitary egg parasitoid, Oobius agrili Zhang and Huang (Hymenoptera: Encyrtidae), is one of several parasitoids that has been introduced to the United States to manage the invasive emerald ash borer (EAB) Agrilus planipennis Fairmaire (Coleoptera: Buprestidae). In order to improve release strategies and establishment of this parasitoid, a better understanding of factors influencing its phenology and fitness is needed. The purpose of this study was to determine the effects of forest microhabitat on the longevity, realized fecundity, and progeny diapause rate of O. agrili. In fall 2019, five reps of two biotypes of laboratory-reared, diapausing O. agrili were deployed at one of three sites: 1) open-air insectary, 2) fragmented urban forest and 3) mature mixed-hardwood forest. Beginning from the spring of 2020, the emergence phenology of overwintered O. agrili from each microhabitat type were monitored daily until its completion. The O. agrili progeny emerging from each microhabitat were continuously reared with fresh EAB eggs under the same microhabitats until late summer and their reproductive fitness parameters (including longevity, fecundity, diapause rate, and population growth) were determined. Overall, microclimatic conditions did not affect O. agrili performance, but O. agrili in the mixed-hardwood treatment emerged later than those in other microhabitats. These findings can be used to inform future O. agrili releases and EAB biological control.