Structure and distribution of antennal sensilla of the red imported fire ant.

The morphology of the antenna of the red imported fire ant, Solenopsis invicta, was examined by light microscopy, scanning electron microscopy, and transmission electron microscopy. The antennae are sexually dimorphic: the worker antenna has porous sensilla on the two distal segments (the antennal club), whereas the clubless male antenna has porous sensilla on all segments past the pedicel. The major type of porous sensilla on both male and female is sensilla tricodea curvata. However, the male s. tricodea curvata are rather uniform in size, whereas the female s. tricodea curvata vary considerably in thickness. The number of sensilla on the distal segment of the worker antenna increases with segment length. This suggests a possible mechanism by which task assignments in S. invicta could be determined by the presence or absence of sensilla sensitive to specific task-related odor or pheromone cues. The sensilla basiconica have an invariant spatial pattern on worker and queen antennae.