Tolerance of immature stages of Drosophila suzukii to high temperature extremes

Tolerance of temperature extremes has not been documented for immature Drosophila suzukii Matsumura (Diptera: Drosophilidae). Bioassays of juvenile D. suzukii were conducted to determine the thermal threshold for survival of immature stages in a controlled laboratory study.  Larvae and pupae aged 1-12 days old were reared in vials on artificial drosophila diet and subjected to a range of elevated constant temperatures for a one-hour period using a heated aluminum slab.  Development of individuals was documented over 3 weeks and emergent adults were counted and removed daily.  Larval development continued within vials following exposure to elevated temperatures when vials were subjected to temperatures below 39 °C; whereas at temperatures above this value, larvae died and pupated individuals never emerged as adults.  Relatively fewer adults emerged at temperatures near this threshold value. At lethal temperatures, larvae attempted to escape from the host substrate, and significantly more larvae were apparent on the surface of substrate of vials exposed to lethal temperatures than in vials exposed to lower temperatures.  To apply this information to field situations, temperature data were taken within a blueberry canopy and on the weed mat floor covering.  In situations where floor management heats dropped fruit above the threshold temperature, fruit drop is unlikely to serve as a reservoir for D. suzukii.  Cultural management to create such inhospitable environments for the insect may decrease in-field pressure at peak times of the growing season.