Sexual difference in antennal sensilla abundance, density and size in Callosobruchus rhodesianus (Coleoptera: Chrysomelidae: Bruchinae)

Sexual difference in antennal sensilla size and per area density has rarely been studied in insects. The bruchine seed beetle Callosobruchus rhodesianus (Pic) (Coleoptera: Chrysomelidae: Bruchinae) is distributed over Central and Southern Africa and is a pest of stored legume seeds, especially cowpeas Vigna unguiculata. Here, we study the type, abundance, morphology and per area density of antennal sensilla on each antennal segment and their sexual differences in C. rhodesianus. The antennae of normal individuals consist of the scape, pedicel and nine flagellomeres as in other congeneric species. Sizes of most antennomeres are larger in males than in females. We observed the following eight different types of antennal sensilla: sensilla trichodea types 1 and 2 (ST1, ST2), sensillacavitae (SCa), sensilla chaetica (SC), sensilla basiconica types 1, 2 and 3 (SB1, SB2, SB3) and Böhm bristles (BB). The SCa is found on all antennomeres unlike in congeners (C. chinensis and C. maculatus). The ST1, the most numerous and longest antennal sensilla type, is denser and thinner in females than in males but more abundant in males than in females. Since the ST1 is considered to serve as a chemoreceptor, the sexual difference in the ST1 may benefit males in searching for mates.