Effects of spinosad-based fruit fly bait GF-120 on tephritid fruit fly and aphid parasitoids

The spinosad-based fruit fly bait GF-120 has recently been developed as a primary tool for the area-wide control and eradication of tephritid fruit flies. In this study, we assessed the direct contact toxicity of GF-120 to three major parasitoids of tephritids in Hawaii: Fopius arisanus (Sonan), Diachasmimorpha tryoni (Cameron), and Pysttalia fletcheri (Silvestri) (Hymenoptera: Braconidae), as well as one aphid parasitoid, Aphidius transcaspicus Telenga (Hymenoptera: Aphidiidae). All four parasitoid species were susceptible to GF-120. Males and females were equally susceptible to GF-120 for all species. The 24-h LC50 values for the opiine braconid species were in a narrow range (8.3-17.5 ppm). The aphidiid appeared to be more susceptible than the opiines, probably due to the stickiness of GF-120. We confirmed that adult F. arisanus (as a model species) do not feed directly on GF-120 either in the presence or the absence of honey and water resources. F. arisanus tasted, discriminated, and gave up GF-120 droplets after a brief (<1 s) mouth examination. Mortality following exposure to GF-120 resulted from close contact. Furthermore, we found that when female F. arisanus were allowed to freely forage on host coffee branches sprayed with droplets at the recommended field rate for use of GF-120 (80 ppm), treatment mortality was significantly higher than control mortality (sprayed with water), and also increased with exposure time. Although GF-120 appears to be the most judicious of reduced-risk fruit fly baits currently available, our results suggest that area-wide application of GF-120 needs to be carefully monitored in situations where release or conservation of parasitoids is a prime concern.