Effects of parental diapause status and release time on field reproductive biology of the introduced egg parasitoid, Oobius agrili (Hymenoptera: Encyrtidae) in the Mid-Atlantic: Implications for biocontrol of the emerald ash borer (Coleoptera: Buprestidae)

Abstract

Oobius agrili Zhang and Huang (Hymenoptera: Encyrtidae), a solitary egg parasitoid native to China, was introduced to the United States for biocontrol of the invasive emerald ash borer (EAB) Agrilus planipennis Fairmaire (Coleoptera: Buprestidae) in 2007. To help develop effective biocontrol-release strategies, we evaluated the effect of parental diapause and release time of the adult parasitoids on their longevity, realized fecundity, and progeny diapause rate under field conditions in the U.S. Mid-Atlantic region in 2016 and 2017. Results from two years of the study showed that both non-diapaused and diapaused O. agrili adults released in rearing containers exposed to field conditions in late spring to early summer (from May 26 to July 20th) successfully survived and reproduced on emerald ash borer eggs provided throughout the study period. The parental parasitoid diapause status and release time did not significantly affect the longevity and life-time fecundity of the released adult parasitoids except that both diapaused and non-diapaused parasitoids released on May 26th of 2017 produced significantly fewer progeny than those from later releases (June 14th and July 20th) of the same year. In both 2016 and 2017, non-diapaused parasitoids consistently produced a higher proportion of diapaused progeny than diapaused parasitoids, regardless of release times. These findings indicate that releases of O. agrili with different diapause status from late spring to early summer may cause variations in establishing overwintering parasitoid populations for biological control of emerald ash borer in the field.