NATURAL THERMAL-STRESS AND HEAT-SHOCK PROTEIN EXPRESSION IN DROSOPHILA LARVAE AND PUPAE

1. Whether Drosophila larvae and pupae naturally experience temperatur es that can cause heat damage or death is poorly understood, but bears directly on numerous investigations of the thermal biology and heat-s hock response in Drosophila. Accordingly, the temperatures of necrotic fruit, which Drosophila larvae and pupae inhabit, the temperatures of larvae and pupae outside the laboratory, and the levels of the heat-s hock protein hsp 70 expressed by larvae in nature were examined. 2. Wh en necrotic fruit was sunlit,internal temperatures rose to levels that can harm indwelling insects, Fruit size and evaporative water loss af fected these temperatures. Temperatures of larvae and pupae in the fie ld commonly exceeded 35 degrees C, with living larvae recorded at >44 degrees C and pupae at >41 degrees C. Natural mortality was evident, p resumably because of heat. 3. In the laboratory, these temperatures ki ll larvae rapidly, with LT(50)s (time taken fur half the sample to be killed) of 30 min at 39 degrees C, 15 min at 40 degrees C and 8.5 min at 41 degrees C. Gradual transfer from 25 degrees C to these temperatu res resulted in no lesser mortality than did direct transfer 4. Hsp 70 levels in lysates of whole larvae were measured by ELISA (enzyme-link immunosorbent assay) with an hsp 70-specific antibody. For larvae wit hin necrotic apples experimentally transferred from shade to sun and w ithin necrotic fruit in situ, hsp 70 levels equalled or exceeded level s detected in parallel laboratory studies of whole larvae or cells in culture, 5. These data provide an ecological context for studies of th ermal stress and the heat-shock response in Drosophila that has hereto fore been lacking.