Venom gland ontogeny in Formicinae, with special reference to the pulvinate convoluted bland (Hymenoptera, Formicidae)

The primordia of the sclerites associated with the Venom gland appear in th ird-stage larvae. The study aims to link the structure and function of this specialised venom structure in Formicinae, together with glandular ontogen y, and puts emphasis on the relevance of the distinguished glandular subuni ts contributing to the final secretion. The most conspicuous changes in gla ndular development occur in the pharate pupa. At this stage, all subunits o f the venom gland (the tubule, the convoluted gland and reservoir) are Visi bly present. Formation of the glandular cuticle starts around day 4 of the pupal stage. Luminal cells in the convoluted gland are provided with abunda nt free ribosomes and apical microvilli that remain during adult life. Stac ks of granular endoplasmic reticulum are also frequently found in these cel ls. The convoluted gland contains relatively few scattered secretory cells, belonging to type 3 according to Noirot and Quennedey (1974), which contai n electron-dense material in their extracellular spaces during adult life. These cells strongly contrast with the apparently general nonglandular natu re of the convoluted gland tubule. Histochemical investigation of the secre tory cells in the pulvinate convoluted gland reveals that these cells conta in Lipoid material, most likely to correspond with lipoids demonstrated in earlier chemical analyses. This lipoidal material in minor quantities stron gly contrasts with the bulk of acid constituting the secretion. The substan ces produced in the convoluted gland could act as insulators, thus protecti ng the insect against its corrosive venom.