Location: Beneficial Insects Introduction ResearchTitle: Patterns of parasitoid host utilization and development across a range of temperatures: implications of climate change for biological control of an invasive forest pest Author
Submitted to: Biocontrol
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/7/2014
Publication Date: 7/23/2014
Citation: Duan, J.J., Jennings, D.E., Williams, D., Kristi, L. 2014. Patterns of parasitoid host utilization and development across a range of temperatures: implications of climate change for biological control of an invasive forest pest. Biocontrol. DOI: 10.1007/s10526-014-9604-9. 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 ambient temperature would affect this parasitic wasp and its relationship with its EAB host 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. In the laboratory study, we examined host attack patterns of this species across a range of temperatures to explore how climate change could affect the interaction with its EAB host. Results from our study showed that the window of EAB egg susceptibility to attack by this wasp declined significantly with increasing exposure to temperatures between 20 to 35°C. In contrast, host attack rate by this wasp increased with ambient temperature between 20 to 25°C, but decreased when temperatures increased between 30 to 35°C. This range of temperature also significantly affected the development, overwintering (or hibernation) and mortality of the wasp with 35oC resulting in 100% mortality. Together, our findings indicate that ambient temperature can profoundly influence EAB egg attack rate by this parasitic wasp. More importantly, the temperature effects are likely to cause differential host attack rates of this parasitic wasp and thus affect its efficacy in suppressing EAB populations in different climate zones or geographic regions.
Technical Abstract: Although climate change has frequently been linked to observed shifts in the distributions or phenologies of species, very little is known about the potential effects of climate change on parasitoids and their relationship with hosts. Using the egg parasitoid Oobius agrili (Hymenoptera: Encyrtidae) we examined host utilization patterns of this species across a range of temperatures to explore how climate change could affect the interaction with its host – the emerald ash borer (EAB) (Coleoptera: Buprestidae), a serious invasive forest pest. Results from our study showed that the window of host susceptibility to O. agrili parasitism declined significantly (from 14.8 days to 2.6 days) in an inverse second order non-linear relationship with increasing exposure temperatures (from 20 to 35°C). In contrast, parasitoid host attack rate changed in a bell-shaped second order relationship – i.e., increased with ambient temperature from 20 to 25°C, but decreased at about the same rate when temperatures increased from 30 to 35°C. This range of ambient temperature also significantly affected the development, diapause and mortality of immature parasitoids with 35oC resulting in 100% mortality. While there was no significant difference in the percentage (20.9-34.9%) of immature O. agrili that entered diapause (as mature larvae), with little (0-4.5%) mortality at 20, 25, and 30°C, there were significant differences in the time event of adult wasp emergence within this temperature range. The median time for 50% of immature O. agrili emerging to adults at 20, 25, and 30°C were 38, 18, and 17 days after parental wasp oviposition, respectively. Together, these findings indicate that ambient temperature can profoundly influence host utilization patterns of O. agrili. More importantly, the non-linear and unequal temperature effects on these host utilization parameters are likely to result in differential host parasitism rates and thus affect their efficacy in suppressing host populations in different climatic zones.