Aedeagal sensilla of Agelastica alni (Coleoptera, Chrysomelidae, Galerucinae)

The intromittent part - the median lobe - of the male copulatory organ - the aedeagus - of beetles is strongly sclerotised and so could give the impression of being just a rigid tube, not providing any sensory input to the male beetle. However, it has already been shown that in many beetle species, the median lobe bears sensilla of different types and in different densities. Here, the morphology of the cuticular elements of putative sensilla on the median lobe of the alder leaf beetle, Agelastica alni (Linnaeus, 1758) and their spatial distribution on this organ are described. There are especially two types of sensilla located in large numbers on the median lobe. One is mamilliform and is probably a bimodal uniporous sensillum, the other is cup-shaped with a pore on top suggesting a contact chemosensor. In addition, there are numerous - presumably mechanosensitive - sensilla basiconica. The density of these sensilla is higher apically and on the lower side than basally and on the upper side of the median lobe. These findings confirm earlier ideas that the male copulatory organs in beetles are not sensory-blind but are sensitive to mechanical and chemical stimuli.