Spotted Wing Drosophila and Control by Parasitoid Wasps — by Ben Diehl

Please Note: Due to Ben's Schedule, We're Meeting on the 5th Monday — Not the 4th!

Spotted wing drosophila, Drosophila suzukii, (or SWD for short) is an invasive species of fly originally from Asia. This pest was first detected in Washington in 2010 and has since become a serious pest of fruit crops. In particular, SWD fundamentally changed management strategies for berry growers in the Pacific Northwest. Unlike related flies that can only attack damaged or rotting hosts (think of the tiny flies that might be attracted to an overripe banana in your kitchen), female SWD possess a saw-like ovipositor that allows them to lay eggs directly into ripe fruit. For many growers the introduction of SWD has therefore resulted in an increase in pesticide applications to avoid harvesting a crop that is infested with SWD maggots. As IPM teaches a holistic approach to pest management, it is important to develop and implement an IPM program using multiple control strategies, rather than only relying on chemical control.

Classical biological control involves surveying natural enemies (predators or parasitoids) in the native range of an invasive species and determining if any would be an appropriate candidate for release as a biological control agent in the pest’s newly established location. As this category of biological control technically involves the release of additional invasive species, laboratory research must be conducted to ensure any non-native predators or parasitoids will not have a significant negative effect on other non-target species. Surveys conducted in the SWD’s native range in Asia identified two parasitoid wasp species, Ganaspis brasiliensis & Leptopilina japonica, as potential candidates for release as biological control agents. Both of these wasps attack SWD larvae by laying eggs inside them while they are hidden inside of fruit. Immature wasps slowly consume the SWD maggot and adult parasitoids hatch from the fly’s pupa. While the biology & host preferences of these species were being investigated in quarantine facilities, wild populations of both species were discovered in southwestern British Columbia in 2019 and subsequently in northwestern Washington in 2020. Our laboratory assisted in several projects aimed to get a better picture of just how far these parasitoid wasps had already spread in western Washington. These projects require the collection of another invasive species, the Himalayan blackberry, Rubus armeniacus, which serves as an alternate host for SWD. By collecting berries infested with SWD maggots, we can rear them in the laboratory and observe them for the emergence of parasitoid wasps.

Ben Diehl has an entomology degree from Texas. He formerly volunteered for Rod at the Burke Museum. He is now a research technologist at the Mount Vernon NW Washington Research & Extension Center.

This meetup will be held as a Zoom meeting. For security reasons, the meeting ID is only available to people who RSVP here, receive the Scarabogram in the mail, or contact the host directly. If you have any trouble or need the meeting ID outside of meetup, please feel free to email the host at jack@mudge.dev. RSVP or email by the morning of the meeting, please! Last-minute additions are likely to be missed. For those who attended any of the last few meetings the zoom number and instructions should be exactly the same. See you Monday!