Sensory organs in the antennae of Phyllophaga obsoleta (Coleoptera: Melolonthidae)

The antennal flagellum of the melolontid beetle Phyllophaga obsoleta Blanchard consists of three terminal plates of lamellae: proximal, middle, and distal. Six types of sensilla were identified on the internal and external surfaces of lamellae from both sexes: placodea (PLAS), basiconica (BAS), coeloconica (COS), auricilica (AUS), chaetica (CHS), and trichodea (TRS). The first four types have been considered as chemoreceptor sensilla and the last two as mechanoreceptor sensilla. The sensilla from the internal and external surfaces of each of three lamellae present in the antennal club from both sexes were mapped by scanning electron microscopy. PLAS were abundant and followed a uniform pattern of distribution on both internal and external surfaces of lamellae from both sexes. Males antennae present a higher number of PLAS in comparison with females antennae. BAS are more abundant in males than in females and follow a more aggregated distribution than PLAS. AUS were included within the BAS group. COS are scarce and only observed on the internal surfaces of all lamellae. TRS and CHS are only present on the periphery of the lamellae. Most sensillar types identified were more abundant in males than in females. The higher number of PLAS observed in males lamellae compared with females lamellae suggests that these sensilla may be involved in sex pheromone reception.