Summary 1.Whether Drosophila larvae and pupae naturally experience temperatures that can cause heat damage or death is poorly understood, but bears directly on numerous investigations of the thermal biology and heat-shock 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-shock protein hsp 70 expressed by larvae in nature were examined. 2. When necrotic fruit was sunlit, internal temperatures rose to levels that can harm indwelling insects. Fruit size and evaporative water loss affected these temperatures. Temperatures of larvae and pupae in the field commonly exceeded 35°C, with living larvae recorded at > 44°C and pupae at > 41°C. Natural mortality was evident, presumably because of heat. 3. In the laboratory, these temperatures kill larvae rapidly, with LT 50 s (time taken for half the sample to be killed) of 30 min at 39°C, 15 min at 40°C and 8·5 min at 41°C. Gradual transfer from 25°C to these temperatures 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 within necrotic apples experimentally transferred from shade to sun and within necrotic fruit in situ, hsp 70 levels equalled or exceeded levels detected in parallel laboratory studies of whole larvae or cells in culture. 5. These data provide an ecological context for studies of thermal stress and the heatshock response in Drosophila that has heretofore been lacking.

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Amphibia, like most vertebrate species, have two forms of GnRH, namely [Arg⁸]GnRH (mammalian GnRH) and [His⁵, Trp⁷, Tyr⁸]GnRH (chicken GnRH II). The differential distribution of the two peptides in the amphibian brain suggests that they may play different roles. Mammalian GnRH, which is found predominantly in the hypothalamus, is most likely the prime regulator of gonadotropin release, while chicken GnRH II, which occurs predominantly in the midbrain and hindbrain, may play a neuromodulatory role. In amphibian sympathetic ganglia, GnRH has been demonstrated to be a neurotransmitter where its release from the presynaptic nerve terminals reversibly inhibits M current, a time- and voltage-dependent potassium current. The occurrence of GnRH in sympathetic ganglia extracts from two amphibian species was investigated. Chicken GnRH II-like immunoreactivity was detected in extracts of bullfrog (Rana catesbeiana) and platanna (Xenopus laevis) sympathetic ganglia after high performance liquid chromatography. Under the chro-matographic conditions used, a second unknown peptide co-eluted with synthetic mammalian GnRH, but showed no cross-reactivity with specific mammalian GnRH antisera. To test the possibility of the presence of a chicken GnRH II receptor in sympathetic ganglion neurones, competition binding of membranes extracted from the sympathetic ganglia of the two amphibian species was investigated with ¹²⁵I-labelled GnRH agonists. The binding of ¹²⁵I-[His⁵, D-Arg⁶, Trp⁷, Tyr⁸]GnRH (a chicken GnRH II agonist) to membranes from the sympathetic ganglia of both amphibian species was specific and had a higher affinity than chicken GnRH II, mammalian GnRH and a mammalian GnRH agonist [D-Ala⁶, NMe-Leu⁷, Pro⁹-NHEt]GnRH. These findings suggest that endogenous chicken GnRH II may play a role in synaptic transmission in the sympathetic ganglia via a receptor specific for chicken GnRH II.

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