Drosophila suzukii has caused a distinct change in small fruit production methods since its invasion in 2008. This small, invasive vinegar fly is known to lay eggs inside both cropped berries and a wide variety of wild, uncultivated fruits. This provides us with a unique system in which to analyze spatial densities of a novel pest across both agricultural and natural areas. In the state of Kentucky, specialty fruit growers report a wide range of damage from D. suzukii and because of this, are in need of an inexpensive, flexible, rapidly implemented management strategy. To explore the cause of varying levels of crop damage, we explored local and landscape level environmental factors that may influence this pest’s population size and density. An immediate assumption may be that D. suzukii would be found in greatest abundance on farms with large acreages of fruit crops. However, discussion of this fly’s intolerance of cold and of non-crop fruiting phenology lend power to dense forest patches as possible insulated refuges for overwintering flies. Over the course of a growing season, we sampled the density of D. suzukii at seventeen farms across central Kentucky. We then quantified the amount of forest cover surrounding each location as a temporary proxy of landscape-level fruit resources. Concurrently, we trialed a novel crop protection strategy by excluding arthropods from three rows of blackberry using a knitted polyethylene net. Within this practical experiment we measured several metrics of crop success and pest presence.
Results/Conclusions
Analysis of D. suzukii population size in relation to percentage of forest cover revealed that the density of this pest is positively correlated with the amount of forest within a small distance of our traps (100 meters). No such correlation was found at a larger scale of forest cover (500 meters). Trapping densities of D. suzukii did significantly vary based on the type of vegetation they were placed in. However, we controlled for this interaction through regimented placement of traps at each farm. Exclusionary netting was found to successfully exclude three pests of blackberry production, Popillia japonica, Cotinis nitida, and frugivorous birds when compared against organic insecticide treatments. Netting also successfully reduced D. suzukii infestation of blackberries, but did not significantly exclude them. Our analyses point to potential management changes that could further reduce D. suzukii pressure for berry growers in the state of Kentucky.