Aberrant venom glands in Amblyoponini (Formicidae, Ponerinae): morphology,ultrastructure and histochemistry

All ants studied so far have a convoluted gland portion as part of their ve nom gland. The venom glands of the amblyoponine genera Amblyopone, Mystrium , Onychomyrmex and Prionopelta, however, are characterized by the absence o f a convoluted gland, which makes this ponerine tribe exceptional among ant s. The venom gland of Amblyoponini is similar to that of mutillid wasps, wh ich supports a possible tiphiid ancestral form. Ultrastructurally, the cell s of the free tubules do not differ from those of most other stinging ants. A separate series of secretory cells, each with its own end apparatus, lin es part of the venom reservoir. These few secretory cells near the orifice of the glandular tubule into the reservoir show an end apparatus with wide extracellular spaces and are similar to those lining the venom reservoir in honeybees. Several muscles run parallel with the longitudinal axis of the reservoir, which results in the curved appearance of replenished reservoirs when these muscles contract. The absence of a bourreleted convoluted gland in Amblyoponini, and the pres ence of only a few lipoidal reservoir cells (histochemical results), when c ompared with histochemistry and ultrastructure of the convoluted gland in o ther Hymenoptera investigated, leads us to conclude that the Amblyoponini m ost likely possess a venom which contains only a fraction of lipoids and/or pheromones, hence suggesting the presence of a mainly proteinaceous venom used against their prey. This idea is supported by the fact that several ot her hymenopteran groups, which are not reported to contain significant amou nts of pheromones in their venom glands, also lack the convoluted gland tis sue.