Hidden host mortality from an introduced parasitoid: Conventional and molecular evaluation of non-target risk
Hepler, J.R., Athey, K., Enicks, D., Abram, P.K., Gariepy, T.D., Talamas, E.J., Beers, E. (2020). Hidden host mortality from an introduced parasitoid: Conventional and molecular evaluation of non-target risk. Insects, [online] 11(11), 1-23. http://dx.doi.org/10.3390/insects11110822
Plain language summary
Classical biological control (CBC), i.e., the release of a natural enemy from the pest’s native range, has long been recognized as a viable approach to controlling invasive pests. CBC, because it now involves rigorous safety testing before implementation, is considered specific to a given pest and does not come with the environmental risks often associated with broad-spectrum chemical pesticides. However, accidentally introduced exotic natural enemies have not undergone screening to ensure safety, and thus may pose environmental risks, specifically to native species that are not the targets of the biological control programs. Some effects of an exotic natural enemy, such as consumption or reproduction, can be measured more readily than others. Our research points out that some of these ‘hidden effects’ can be quite important and merit our attention. We use molecular tools and modeling to help understand the hidden effects both for the target and non-target species. Our model system was an invasive fruit and vegetable pest from Asia, the brown marmorated stink bug (BMSB), Halyomorpha halys, and an exotic parasitoid, Trissolcus japonicus. T. japonicus has become established in North America and could help limit outbreaks of this pest. Unfortunately, it also kills non-target stink bugs with varying degrees of reproductive success, which may have both direct and indirect ecological effects on H. halys and non-target stink bug species.
Hidden trophic interactions are important in understanding food web ecology and evaluating the ecological risks and benefits associated with the introduction of exotic natural enemies in classical biological control programs. Although non-target risk is typically evaluated based on evidence of successful parasitism, parasitoid-induced host mortality not resulting in visible evidence of parasitism (i.e., nonreproductive effects) is often overlooked. The adventive establishment of Trissolcus japonicus, an exotic parasitoid of the introduced stink bug Halyomorpha halys, provides an opportunity to investigate the total impact of this parasitoid on target and non-target hosts in the field. We developed a new methodology to measure nonreproductive effects in this system, involving a species-specific diagnostic PCR assay for T. japonicus. We applied this methodology to field-deployed eggs of four pentatomid species, coupled with traditional rearing techniques. Nonreproductive effects were responsible for the mortality of an additional 5.6% of H. halys eggs due to T. japonicus, and were even more substantial in some of the non-target species (5.4–43.2%). The observed hidden mortality of native non-target species from an introduced parasitoid could change predictions about direct and indirect ecological interactions and the efficacy of biological control of the target pest.