Additives to enhance chemical control of Drosophila suzukii
Abstract: Drosophila suzukii has worldwide become one of the most destructive pests in soft fruits. Keeping fruit free from infestation is challenging, but mandatory since there is a zero tolerance for larvae in fruit. Even with application of pesticides at short intervals, this is not always achievable. Therefore, means to improve the effectiveness of insecticides against D. suzukii were investigated. In this article, we focalize additives which are mixed with the insecticide solution to improve oral uptake by D. suzukii. Tested products were white sugar 0.2%, brown sugar 0.2%, Attracker® 0.2%, Combi-Protec® 0.2%, Blossom Protect® 0.1% and a mixture of baking yeast 0.125% (Saccharomyces cerevisiae) and brown sugar 0.125%. A wetting agent, Trend® 0.1%, was also included. The products were tested in the laboratory for their feeding enhancing ability. Furthermore, it was determined, both in lab and field, if this could actually improve chemical control of D. suzukii. In the laboratory assays, it was observed that both sugar and protein containing substances could improve D. suzukii feeding. A non-significant shift in preference was revealed concordantly by two assays: at the beginning of these trials sugar-based feeding enhancers are preferred by D. suzukii, but as the tests progress this preference shifts to protein based products. The feeding-enhancing ability could induce increased mortality rates in a lab trial: the mixture of baking yeast and brown sugar significantly increased the mortality caused by cyantraniliprole after 16 hours. Brown sugar alone and Combi-Protec® also increased the mortality after 16 hours, but this was not significant. After 24, 48 and 72 hours no feeding enhancer could improve the mortality in a significant manner. The wetting agent Trend® significantly decreased the mortality at 16 and 24 hours. This drop in mortality was so pronounced that there was no significant difference any more with the untreated control. In the field trial in a cherry orchard only the mixture of baking yeast 0.2% and brown sugar 0.2% was able to improve the effect of spinosad on all three sampling dates although not significant. In conclusion, the mixture of baking yeast and brown sugar was the best feeding enhancer, both in lab (significant) as in field (not significant). The wetting agent Trend® 0.1% was revealed as an antifeedant in the lab (significant).