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Plant-Insect Ecosystems

Poster: P-IE, Biocontrol

D3398: Is photoperiod induced diapause a bet hedging strategy for Oobius agrili, the introduced egg parasitoid of emerald ash borer?

Tuesday, November 12, 2024
9:00 AM – 5:00 PM MST
Location: Phoenix Convention Center, Exhibit Hall 6, PCC
Poster Display
Oobius agrili Zhang and Huang (Hymenoptera: Encyrtidae) is an egg parasitoid, native to Asia, that has been released in North America to manage emerald ash borer (EAB), Agrilus planipennis Fairmaire (Coleoptera: Buprestidae). Shortened photophases induce Oobius agrili diapause which is modulated by the parasitoid larva developing within the EAB egg. Because EAB eggs are usually hidden in bark cracks or under bark flakes on ash trees, we conducted studies to determine how the location of EAB eggs affects parasitoid diapause induction in the field. EAB eggs parasitized by O. agrili were placed under bark flaps or on the surface of cut ash bolts that were suspended from trees in the field. We selected trees that were either shaded or in direct sunlight.  Parasitized EAB eggs were deployed from mid-July to early September during 2021 and 2022. Results indicated that parasitoids in eggs under bark flaps were much more likely to enter diapause than parasitoids in eggs on the bark surface, regardless of ambient photophase. Also, more parasitoids entered diapause on shaded trees compared to trees in the direct sunlight.  We propose that photoperiod induced diapause serves as a bet-hedging strategy for O. agrili whereby parasitoids in hidden eggs enter diapause because they are more likely to survive predation and abiotic factors. In contrast, parasitoids in exposed eggs on the bark surface are more vulnerable to mortality from predation and abiotic factors and therefore emerge as adults, but at the risk of not finding suitable hosts before EAB oviposition ends.