Climate variation alters the synchrony of host–parasitoid interactions

Authors: WETHERINGTON, MILES - University Of Maryland; JENNINGS, DAVE - University Of Maryland; SHREWSBURY, PAULA - University Of Maryland; Duan, Jian

Submitted to: Ecology and Evolution
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/26/2017
Publication Date: 12/1/2017
Citation: Wetherington, M.T., Jennings, D.E., Shrewsbury, P.M., Duan, J.J. 2017. Climate variation alters the synchrony of host–parasitoid interactions. Ecology and Evolution. 7(20):8578-8587. https://doi.org/10.1002/ece3.3384.
DOI: https://doi.org/10.1002/ece3.3384

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 since 2007 and successfully established at most release sites in the US. Understanding how variation in ambient temperature will affect the interaction (or synchronization) between this parasitoid and its EAB host is important for us to predict its efficacy under conditions of climatic changes. In a laboratory study, we examined EAB oviposition (or fecundity) and the parasitoid-host attack patterns across a range of temperature variations to explore how climate change could affect the interaction with its EAB host. Results from our study showed that temperature variation significantly changed the egg laying pattern of EAB, with a shorter duration of egg laying at higher temperature variations. Additionally, even moderate increases in temperature variation significantly affected parasitoid emergence times, while decreasing parasitism rates and survival. Thus, relatively small changes in the frequency and severity of extreme temperature events have the potential to disrupt the seasonal synchronization between EAB and its egg parasitoid. More importantly, these results indicate how future climate change could affect various life-history parameters in insects. Our findings are also particularly pertinent for biological control programs where failed introductions of parasitoids could enable unregulated population growth of pest species.

Technical Abstract: Although some research has examined how parasitoids will respond to colder temperatures or experimental warming, we know relatively little about how increased variation in temperature could affect interactions between parasitoids and their hosts. Using a study system consisting of emerald ash borer (EAB), Agrilus planipennis (Coleoptera: Buprestidae), and its egg parasitoid Oobius agrili (Hymenoptera: Encyrtidae), we conducted a series of environmentally-controlled laboratory experiments to investigate how increased seasonal temperature variation affected the synchrony of host-parasitoid interactions. We hypothesized that increased temperature variation would lead to decreases in: 1) host and parasitoid survival, 2) host fecundity, and 3) parasitoid attack rates, independent of host density. EAB were reared in environmental chambers under four different temperature variation treatments (standard deviations of 1.24, 3.00, 3.60, and 4.79°C), while O. agrili experiments were conducted in the same environmental chambers using a 4 x 3 design (4 temperature treatments x 3 EAB egg densities). We found that EAB fecundity was negatively associated with temperature variation, and that temperature variation significantly changed the temporal egg laying distribution of EAB, with a shorter oviposition duration at higher temperature variation treatments. Additionally, even moderate increases in temperature variation significantly affected parasitoid emergence times, while decreasing parasitism rates and survival. Thus, relatively small changes in the frequency and severity of extreme temperature events have the potential to phenologically isolate emerging parasitoids from viable host eggs, which in the absence of alternative hosts could lead to localized extinctions. More broadly, these results indicate how future climate change could affect various life-history parameters in insects. Our findings are also particularly pertinent for biological control programs where failed introductions of parasitoids could enable unregulated population growth of pest species.