Effects of droplet size, density, and concentration of a spinosad bait spray on control of Drosophila suzukii (Diptera: Drosophilidae)

The use of spinosad bait spray effectively controls Western cherry fruit fly and minimizes nontarget effects on beneficial arthropods.  Spotted wing drosophila (SWD) (Drosophila suzukii (Matsumura)) control also relies on the active ingredient spinosad, but bait spray use, as opposed to canopy sprays, has not been successful. To justify the reintegration of this technique into cherry pest management, we investigated the effects of droplet size, droplet density, and different concentrations of GF-120 on SWD in separate trials.  We exposed female SWD to droplets placed on leaves in small cages, with fruit suspended in the foliage as an oviposition substrate.  Oviposition punctures were evaluated after 24 h, and mortality was evaluated after 24 and 48 h.  Cherries were incubated for 21 d, and emerged adults from the ovipositions were counted. Higher droplet densities produced higher mortality levels at 24 h, but mortality was close to 100% at 48 h in all treated cages. Oviposition punctures were significantly suppressed by both densities of the 250-μl droplet study compared to the check, but only in the higher rate in the 25-μl droplet study. The numbers of emerged adults reflected oviposition counts. Droplets of all concentrations caused significantly higher mortality than the check, but not in order of increasing concentration.  As in the previous tests, mortality was about 100% by 48 h, and ranged from 26-54% at 24 h.  Ovipositions were significantly lower than the check in the 1:3 dilution of GF-120, but not in other concentrations.