Pupation depth of spotted wing drosophila (Drosophila suzukii) and effects of field sanitation in Florida strawberries

Spotted wing drosophila (Drosophila suzukii) is a relatively new invasive pest of small fruits in many temperate regions worldwide. Adult females possess large, serrated ovipositors that allow penetration into partially ripe and ripe fruit. Larvae render fruit unmarketable and cause economic losses. Monitoring and management tactics have focused on the adult stage, but less is known about factors affecting behavior and survival of immature stages. In this study, mature D. suzukii larvae were placed on the surface of sandy soil from two strawberry fields in Florida, each at three moisture levels (dry [0% moisture], field level [7.5%], and saturated [15%]). In the laboratory, 79-86% of larvae desiccated or pupated visibly on the surface of dry soils, while 93-100% of larvae pupated 1-6 mm below the surface of field level or saturated soils. In the field, over 90% of larvae desiccated or pupated on the surface of dry soils, and 80-90% of larvae pupated 1-6 mm below the surface in field level or saturated soils. Removal of unmarketable strawberries from field plots versus discarding them in row aisles had no measurable effect on D. suzukii levels in marketable fruit, but more larvae of other Drosophila spp. were found in marketable from plots where unmarketable fruit was discarded in aisles. Further research is needed to determine the effect of soil type and moisture level on pupal survival and emergence success.