Control strategies for Rhagoletis mendax disrupt host-finding and ovipositional capability of its parasitic wasp, Diachasma alloeum

Diachasma alloeum (Muesebeck) is a braconid parasitoid of Rhagoletis mendax Curran and Rhagoletis pomonella (Walsh). Laboratory choice tests using a Y-tube olfactometer compared behavioral responses of D. alloeum to various olfactory stimuli. More than 25% of naïve D. alloeum females, never having experienced R. mendax or blueberries, were 'innately' attracted to volatiles emitted from uninfested blueberry fruit. Experience with R. mendax-infested blueberry fruit approximately doubled the proportion of D. alloeum that subsequently responded to volatiles from uninfested blueberry fruit and decreased the time required to elicit this behavior compared with naïve wasps. Volatiles emanating from infested blueberry fruit, that were oviposited into by R. mendax 16-19 d prior to the assay, attracted four and two times more naïve and experienced D. alloeum, respectively, than uninfested fruit or fruit one day post-R. mendax oviposition. Although parasitoids were found to be attracted to blueberry volatiles in the lab, we hypothesized that insecticide applications targeting R. mendax could interfere with the wasps' normal host-finding behavior. In field studies, blueberry fruit treated with the neonicotinoid insecticide imidacloprid (Provado 1.6 F) and the kaolin-clay particle film Surround WP, eliminated parasitization of R. mendax by feral D. alloeum. Blueberry fruit treated with the kaolin-clay particle film was equally attractive to D. alloeum as untreated and infested fruit. But, the use of kaolin clay prevented wasps from ovipositing into berries after alighting. The results of this study imply that current management tools for R. mendax may negatively impact the importance of D. alloeum as a biocontrol agent of Rhagoletis flies.