2010 Annual Report 1a.Objectives (from AD-416) Although aphid endosymbionts are known to confer resistance to attack by some parasitoid species, very little is known about the impacts such endosymbionts have on biological control of pest aphids. We will determine whether the aphid endosymbiont HAMITONELLA DEFENSA affects parasitism by APHELINUS species being considered for introduction against pest aphids. 1b.Approach (from AD-416) We will test whether parasitism of APHIS CRACCIVORA by APHELINUS species that are candidates for introduction against soybean aphid is affected by the presences of HAMITONELLA DEFENSA. 3.Progress Report The heritable bacterial symbiont, HAMILTONELLA DEFENSA, protects the pea aphid from attack by parasitoid wasps. Preliminary data suggest that H. DEFENSA also defends cowpea aphid, APHIS CRACCIVORA, against parasitoids. However, the bacterium may not protect the aphids equally well across parasitoid taxa because some parasitoids have eggs that absorb nutrients during development (hydropic, e.g. braconids) and others have eggs that do not (anhydropic, e.g., aphelinids). We are testing the hypothesis that H. DEFENSA-infected A. CRACCIVORA resist parasitism by APHELINUS species. We will compare results from this aphelinid which has anhydropic eggs with those from braconid species with hydropic eggs. Monitoring was achieved through frequent telephone calls and emails.