Ring gland and prothoracic gland sensitivity to interspecific prothoracicotropic hormone extracts

Using the techniques of intraspecific in vitro activation of prothoracic glands and ring glands by serial dilutions of prothoracicotropic hormone (PTTH) extracts from pupal Manduca sexta (Lepidoptera) and larval Sarcophaga bullata (Diptera), a dose-response of activation was observed for both species. In both species maximum activation was at 0.5 brain equivalents while the number of brain equivalents necessary for half maximal stimulation (ED50) was 0.20 for Manduca and 0.15 for Sarcophaga. When prothoracic glands or ring glands were challenged with interspecific PTTH extracts from a stage different from that of the gland donor, no dose-response of gland activation was observed. However, when M. sexta larval prothoracic glands were challenged by S. bullata larval PTTH extract, activation was observed. The dose-response profile fell midway between the dose-response curves obtained for the intraspecific assays. Thus, PTTH extract from one insect has the ability to activate the prothoracic glands of an insect representing another order.