Developing an artificial diet for rearing Ganaspis brasiliensis (Hymenoptera: Figitidae) on spotted-wing drosophila

Drosophila suzukii (Matsumura) (Diptera: Drosophilidae) is a global invasive pest attacking soft-skinned fruit. The specialist larval parasitoid wasp, Ganaspis brasiliensis (Ihering), was recently approved in Europe and the United States for classical biological control releases against D. suzukii. Rearing methods are essential for supporting innundative releases but current methods using fresh fruit are costly and susceptible to variation in host quality. To develop an artificial rearing system, we first compared the performance and development of D. suzukii and G. brasiliensis on fresh raspberries and blueberries and then on various artificial diet shapes and volumes. Drosophila suzukii had 1-2 days shorter development times in raspberry than blueberry, whereas Ganaspis adult development time was similar in both fruit and averaged 25 days. Parasitism rates by G. brasiliensis were significantly higher in blueberry than raspberry in both small and large resource patches. We found that D. suzukii preferred to lay eggs in full sphere diet shapes than in flat diet circles or semisphere diet, and in the first trial with wasps parasitism was only found on D. suzukii larvae in the full sphere shape of raspberry diet. Comparison of parasitism on full sphere raspberry and blueberry diets found higher parasitism in raspberry compared to blueberry diet. Our results indicate potential for further improvement of artificial rearing systems for G. brasiliensis to allow more cost-effective and reliable rearing for biological control programs.