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Mating elicits two well-defined reactions in sexually matured females of many insects: reduction of receptivity and increased oviposition. These post-mating responses have been shown to be induced by factors synthesized in the reproductive tract of the adult male and transferred in the seminal fluid to the female during copulation. One of these factors, named sex-peptide (SP), has been identified in Drosophila melanogaster. Using an in vitro radiochemical assay, we show that synthetic sex-peptide considerably activates juvenile hormone III-bisepoxide (JHB3) synthesis in corpus allatum (CA) excised from Days 3 and 4 post-eclosion virgin females. Base levels are significantly lower at emergence (Day 0) than on subsequent days, and only weak stimulation is obtained on Day 1, while none is obtained on Day 2, where maximal basal synthesis occurs. The CA of mated females cannot be stimulated further for at least 7 days, but regain responsiveness by Day 10 after mating. Synthesis of JHB3 stimulated by SP in vitro persists for at least 4 h after removal of the peptide. Development of responsiveness of the CA to SP in vitro is compared with development of the post-mating reactions of sex-peptide injected virgin females. Our results suggest that the CA is a direct target for SP in vivo and that sexual maturity is established separately for the two post-mating reactions.

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Mating elicits two well‐defined reactions in sexually matured females of many insects: reduction of receptivity and increased oviposition. These post‐mating responses have been shown to be induced by factors synthesized in the reproductive tract of the adult male and transferred in the seminal fluid to the female during copulation. One of these factors, named sex‐peptide (SP), has been identified in Drosophila melanogaster. Using an in vitro radiochemical assay, we show that synthetic sex‐peptide considerably activates juvenile hormone III‐bisepoxide (JHB3) synthesis in corpus allatum (CA) excised from Days 3 and 4 post‐eclosion virgin females. Base levels are significantly lower at emergence (Day 0) than on subsequent days, and only weak stimulation is obtained on Day 1, while none is obtained on Day 2, where maximal basal synthesis occurs. The CA of mated females cannot be stimulated further for at least 7 days, but regain responsiveness by Day 10 after mating. Synthesis of JHB3 stimulated by SP in vitro persists for at least 4 h after removal of the peptide. Development of responsiveness of the CA to SP in vitro is compared with development of the post‐mating reactions of sex‐peptide injected virgin females. Our results suggest that the CA is a direct target for SP in vivo and that sexual maturity is established separately for the two post‐mating reactions. © 1996 Wiley‐Liss, Inc.

After mating, Drosophila melanogaster females lay substantially more eggs and mate rarely. Central to these changes is Sex peptide (SP), a male peptide transferred into the female during copulation. Injected into virgins, SP induces the same post mating response as observed after mating. In this study we investigated the role of the mushroom body (MB) in the SP response system. The SP response of females with either chemically ablated or mutant MBs was analyzed. After injection of SP, females with chemically ablated MBs reduce their receptivity and increase their ovulation and oviposition to the level of females with intact MBs. Virgin females with ablated MBs, however, show a constitutively elevated oviposition rate. Hence in untreated females, MBs are not implicated in the SP-induced reduction of receptivity and increase of ovulation. However, they depress the oviposition rate of virgins. Thus, SP has two functions for oviposition: it de-represses the MB-dependent block on the egg laying activity of virgins and additionally stimulates oviposition. SP-injected mushroom body miniature (mbm) females lay fewer eggs, ovulate less frequently, and mate more often than wild-type females. A model of the putative role of MBs and the gene product of mbm in SP-induced oviposition is presented.

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