Reproductive biology and diapause patterns of Oobius agrili, an egg parasitoid of the emerald ash borer (Agrilus planipennis)

Oobius agrili (Hymenoptera: Encyrtidae) is a solitary egg parasitoid of the invasive emerald ash borer (Agrilus planipennis) that has been introduced to the U.S for biological control. I investigated the reproductive biology of O. agrili and characterized the weekly survivorship, fecundity, and diapause patterns of both pre-diapaused and post-diapaused populations of O. agrili under four different temperature-photophase treatments: (1) warm (30 °C) with long-day (16 h) photophase, (2) warm (30 °C) with short-day (8 h) photophase, and (3) cold (20 °C) with long-day (16 h) photophase, and (4) cold (20 °C) with short-day photophase (8 h). Results of this study showed that regardless of the length of photophase, parental wasps of both pre-diapause and post-diapause O. agrili survived significantly longer at 20 °C than at 30 °C. Both pre and post-diapaused O. agrili wasps deposited their egg load rapidly at 30 °C compared to those at 20 °C which laid eggs more steadily over time. Pre-diapaused O. agrili laid significantly fewer eggs at 20 °C than at 30 °C, whereas there was no significant difference in lifetime fecundity totals between the treatments in the post-diapaused O. agrili population. Higher proportions of the progeny produced by both pre-diapause and post-diapause O. agrili were induced into obligatory diapause by short-day (8 h) photophase, regardless of rearing temperature. In addition, the post-diapause wasps in both short-day and long-day photophase treatments produced increasing proportions of diapaused progeny over time, whereas there were no significant differences in the proportions of diapaused progeny by pre-diapause wasps over different sampling times. These findings indicate that post-diapause wasps should be released in late May when temperatures are still relatively low (~20 °C) to synchronize with emerald ash borer oviposition and effectively establish multiple generations per season.