Effects of temperature and photoperiod on the reproductive biology and diapause of oobius agrili (Hymenoptera: Encyrtidae), an egg parasitoid of emerald ash borer (Coleoptera: Buprestidae)

Authors: HOBAN, JACQUELINE - University Of Delaware; Duan, Jian; HOUGH-GOLDSTEIN, JUDY - University Of Delaware

Submitted to: Environmental Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/7/2016
Publication Date: 5/3/2016
Citation: Hoban, J., Duan, J.J., Hough-Goldstein, J. 2016. Effects of temperature and photoperiod on the reproductive biology and diapause of oobius agrili (Hymenoptera: Encyrtidae), an egg parasitoid of emerald ash borer (Coleoptera: Buprestidae). Environmental Entomology. 45(3):726-731. doi: 10.1093/ee/nvw034.

Interpretive Summary: Oobius agrili is a parasitic wasp that attacks eggs of the Emerald ash borer (EAB), which is a serious invasive pest of North American ash trees. This parasitic wasp has been released as a biological control agent for EAB in the US for several years. Understanding how photoperiod and ambient temperature would affect the reproduction and survivorship of this parasitic wasp is important for us to predict its efficacy in different climate zones or regions where it has been or will be released for biological control. Scientists from the University of Delaware and the ARS laboratory in Newark, DE examined the weekly survivorship, fertility, and overwintering patterns of adult wasps under four different temperature-day length combinations: 30°C (warm) and 20°C (cold) temperatures with long-day (16 h) and short-day (8 h) light periods. Results showed that regardless of the photoperiod, parental wasps survived significantly longer at 20 °C than at 30 °C, but laid their eggs faster at 30 °C compared to those at 20 °C. Higher proportions of the wasp’s offspring entered overwintering stages in short-day (8 h) photoperiod, regardless of rearing temperature. These findings are important to the improvement of the current rearing program for increased production of this biocontrol agent, which indicate that the parental wasp should be continuously reared under warm temperature and long-day photoperiod. These results will lead to higher numbers of released agents and thus improved control of EAB in infested regions.

Technical Abstract: Oobius agrili Zhang and Huang is a solitary egg parasitoid of the invasive emerald ash borer, Agrilus planipennis Fairmaire (Coleoptera: Buprestidae) and has been introduced to the United States for biological control. We characterized the weekly survivorship, fecundity, and diapause patterns of both pre- and post-diapause populations of O. agrili under four different temperature-photophase combinations: 30°C (warm) and 20°C (cold) temperatures with both long-day (16 h) and short-day (8 h) photophase. 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 laid their eggs faster at 30 °C compared to those at 20 °C. Higher proportions of the progeny produced by both pre-diapause and post-diapause O. agrili wasps were induced into 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 no significant differences were observed in the proportions of diapaused progeny by pre-diapause wasps over different sampling times. These findings suggest that O. agrili should be continuously reared under warm temperature and long-day photoperiod (to avoid diapause and increase reproduction). In addition, we recommend that post-diapause wasps be used for field releases in early summer when temperature is still relatively low (~20 °C) and host eggs are available so that they can reproduce multiple generations prior to overwintering.