CENTRAL PROJECTIONS OF THE SENSORY HAIRS ON THE GEMMA OF THE ANT DIACAMMA - SUBSTRATE FOR BEHAVIORAL MODULATION

In the ant genus Diacamma, all workers eclose from their cocoons with little clublike thoracic appendages, called gemmae. Whether these gemmae are mutilated determines individual behaviour, and ultimately reproductive role, in two of the three species examined. The gemmae are covered with sensory hairs, which probably serve a mechanoreceptive function. The sensory afferents arising from these hairs were stained and traced into the central nervous system (CNS). They feature widely distributed collaterals invading all three thoracic ganglia as well as the suboesophageal and the second abdominal ganglia. The multisegmental arborization pattern of the gemma afferents is very similar to that of wing-hair afferents of other ants (queens and males) or other insects in general. This implies that gemmae and wings are homologous structures. We discuss the morphology of the gemma afferents with respect to their possible involvement in the behavioural changes associated with mutilation. The neuronal processing may be modulated by (1) the decrease of sensory input onto interneurons (suggested by the afferents' extensive arborizations); or (2) by the effect of neuromodulatory substances (suggested by the finding that terminals occur within the cell body rind of the ganglion).