A closer look at the antennae of the invasive Halyomorpha halys: fine structure of the sensilla

The brown marmorated stink bug, Halyomorpha halys, is an invasive agricultural and urban pest capable of feeding on over 100 species of host plants. The antennae of this bug play an important role not only in detecting food and mates but also in short-range location of conspecifics when aggregating for diapause. The morphology and distribution of antennal sensilla of H. halys were investigated at an ultrastructural level using scanning and transmission electron microscopy approaches. Adults have 5-segmented antennae, made up of a scape, a 2-segmented pedicel and two flagellomeres, while 5th instar nymphs have shorter, 4-segmented antennae, with only one pedicel segment. Five types of sensilla are distinguished, based on their shape, length and basal width and the presence of basal socket and pores: sensilla basiconica (types A, B, C, D and E), sensilla coeloconica, sensilla trichoidea and sensilla chaetica (types A and B). Sexual dimorphism was not observed in this species, with respect to the morphological features and abundance of sensilla. The most abundant sensory structures are sensilla trichoidea showing characteristics typical of olfactory sensilla, whereas the least abundant are sensilla coeloconica which may be involved in thermo- and hygro-reception. Basiconic sensilla type A are solely identified on the antennae of 5th instar nymphs, where they presumably have a dual mechanosensorygustatory role. The putative function of the remaining sensilla are herein discussed.