Differences in the reproductive biology and diapause of two congeneric species of egg parasitoids (Hymenoptera: Encyrtidae) from northeast Asia: Implications for biological control of the invasive emerald ash borer (Coleoptera: Buprestidae)

•The emerald ash borer (EAB) is a serious invasive pest of North American ash trees.•Oobius primorskyensis and O. agrili are egg parasitoids having potential for EAB biocontrol.•Diapaused O. primorskyensis lives significantly longer and produces significantly more progeny than the non-diapaused type.•Diapaused O. agrili lives significantly shorter and produces significantly less progeny than the non-diapaused type.•Non-diapaused adults of both species produce a significantly higher proportion of diapaused progeny than diapaused adults.

The emerald ash borer Agrilus planipennis (Coleoptera: Buprestidae) is a serious invasive pest that has killed millions of North American ash (Fraxinus spp.) trees in the United States and Canada since its first detection in 2002. Oobius primorskyensis Yao and Duan and Oobius agrili Zhang and Huang (Hymenoptera: Encyrtidae) constitute a cryptic species complex of egg parasitoids attacking A. planipennis in their native range of northeast Asia. While O. primorskyensis is currently being evaluated in quarantine for potential biocontrol introduction against A. planipennis to the U.S., O. agrili has established populations in some areas of the U.S. since its first introduction in 2007. In the present study, we quantify and compare the survivorship, fecundity and progeny diapause between O. primorskyensis and O. agrili for both diapaused and non-diapaused types. Both parasitoid species were reared in the laboratory with fresh A. planipennis eggs at 25 ± 1 °C, ≈65% RH, and 16: 8 h L: D photoperiod. Results of the study demonstrate that there are distinctive differences in the reproductive biology and progeny diapause pattern between the two parasitoid species as well as between diapaused and non-diapaused types within each species. Adults of diapaused O. primorskyensis had significantly longer longevity and produced significantly more progeny over their lifetime than diapaused adult O. agrili. Although there was no significant difference in their longevity, adults of the non-diapaused O. priomorskyensis produced significantly less progeny than those of non-diapaused O. agrili. While a majority (>64%) of the progeny produced by diapaused O. primorskyensis and both diapaused and non-diapaused O. agrili continued development to adults, nearly 100% of the progeny from non-diapaused O. primorskyensis entered diapause. These findings suggest that the effectiveness of O. priomorskyensis and O. agrili in classical biocontrol of A. planipennis may vary in different regions of North America, where the host phenology in adult emergence and oviposition may differ. Our study indicates that O. priomorskyensis and O. agrili may be complementary to each other in biocontrol of A. planipennis in regions where both species can be successfully established.

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