More Power with Flower for the Pupal Parasitoid Trichopria drosophilae: A Candidate for Biological Control of the Spotted Wing Drosophila

Parasitoids are currently considered for biological control of the spotted wing drosophila (SWD) in berry crops. Releases of mass-reared parasitoids require the presence of all resources necessary to ensure their effectiveness in the crop system. The use of floral resources to feed Trichopria drosophilae, one of the candidate species, was investigated in a laboratory study. The life expectancy of males and females increased by three to four times when they had access to flowers of buckwheat or of two cultivars of sweet alyssum. Female realized lifetime fecundity increased from 27 offspring/female exposed to water only to 69 offspring/female exposed to buckwheat flowers. According to this almost threefold increase in parasitoid fitness, it is advisable to introduce flowering plants into the crop system, when parasitoid releases are carried out. Sweet alyssum offers the advantage of not growing too tall in combination with an extended blooming. However, adult SWD were also able to feed on flowers of both plants and survived for at least 27 days, much longer than starving flies. The introduction of flowering plants to promote natural enemies therefore requires further consideration of the risk-benefit balance under field conditions to prevent unintended reinforcement of this pest.