Year-round trap capture of the spotted-wing drosophila,Drosophila suzukii (Diptera: Drosophilidae), in Korean strawberry greenhouses

Korean greenhouse strawberries are mostly cultivated from October to May, which includes the cold winter season. During this time, the population size of the spotted-wing drosophila (SWD), Drosophila suzukii Matsumura (Diptera: Drosophilidae), is expected to decrease in the wild, and is also expected to decrease inside the greenhouses, as long as SWD are not already present inside. Field surveys of SWD have been extensively carried out for field-grown agricultural fruits, but no study has been conducted for greenhouse fruits, such as strawberries. In this study, SWD capture patterns were examined inside and outside of the greenhouse blocks, and in the nearby woodlands in a southwestern locality of Korea using selected traps and attractants for nearly 19 months—in addition to several greenhouse blocks—during the strawberry cultivating periods. The highest capture period was observed from October to mid-December in woodlands, whereas capture number subsequently and sharply decreased up to mid-April, resulting in mostly zero-captures or low captures (≤10). During this period, a zero-capture period was observed inside the greenhouse that lasted for nearly three months (late December to late February). An incubation of the fallen strawberries supported the results of trap capture from inside the greenhouses. Taken together, the occurrence of SWD in the strawberry greenhouses is likely to be highly dependent on that of the nearby woodlands. Thus, a sharp winter drop and the subsequent zero- or low-capture periods in the woodland areas were likely responsible for the observed zero-capture periods inside the greenhouses.