Submitted to: Journal of Biological Control
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/7/2011
Publication Date: 9/16/2011
Citation: Banks, J., Stark, J., Vargas, R.I., Ackleh, A.S. 2011. Parasitoids and ecological risk assessment: can toxicity data developed for one species be used to protect an entire guild?. Journal of Biological Control. 59(3):336-339. Interpretive Summary: Parasitoids are famously effective biological control agents, adept at finding, tracking, and regulating host populations, and are the primary control agents for many economically important crop pests. However, parasitoid populations can also be quite susceptible to the effects of chemical pesticides. Most integrated pest management regimes involve the use of some level of chemical pesticides, the compatibility of parasitoid and chemical control has beem the subject of many lab and field studies. Often, more commonplace parasitoid species are substituted for species that may be rare or endangered. These "surrogate species" are usually chosen based on taxonomic or phylogenetic similarities, and in many cases represent a reliable alternative to testing. The objective of this study is to determine whether or not we can accurately predict pesticide impacts on a guild of parasitoid species by determining the effects on any one "representative" species. Four parasitoid species varied widely in fecundity reduction thresholds. D. rapae was the most robust, withstanding a 65% decrease in fecundity before going extinct. At the other extreme, P. fletcheri was the most sensitive, driven to extinction after only a 12% reduction in fecundity. F. arisanus and D. longicaudata had similar susceptibilities, both persisting up to levels of slightly more than 40% fecundity reductions. Results suggested that we should exercise caution in assuming that all biological control agents will respond similarly to chemical pesticide disturbances.
Technical Abstract: Parasitoid wasps are important control agents for a suite of economically important anthropod pests. However, it is well known that hymenoptera in general are highly vulnerable to the effects of chemical pesticides, and so represent an opportunity to better understand the compatibility of biological and chemical control of pests. Closely related species are often used in trial aimed at assessing the effects of different chemical toxicants on hymenoptera. Most of these tests focus on acute toxicity, with few exploring longer-term population outcomes. Here, using a simple mathematical framework, we quantify the relative vulnerability of a suite of parasitoids species to the sublethal effect of a toxicant acting on fecundity. Using an equation that describes a critical extinction threshold, we calculate levels of reduction in fecundity above which parasitoid species important for biological control are driven to local extinction. We apply this framework to four economically important braconid biological agents (Diachasmimorpha longicaudata, Psyttalia fletcheri, Fopiuarisanus, and Diaeretiella rapae), and find that threshold levels vary widely among them. In particular, we find that D. rapae is far more robust to pesticide exposure than the other three species, suggesting that these four species are not interchangeable in terms of risk assessment. Our findings imply that caution should be exercised in assuming species even within the same functional guild may be used as surrogate species for one another.