Morphology and ultrastructure of the antennal sensilla of Sitophilus granarius (Coleoptera: Curculionidae)

Sensilla are sense organs in insects, typically consisting of a group of cuticle or epidermal cells that appear as hairs or rod-shaped structures. Sensilla serve as the functional elements of sensory systems. The goal of this study was to determine the type and distribution of sensilla in the antennae of Sitophilus granarius (L.) using light microscopy, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). This is one of the first studies in which the morphology and distribution patterns of sensilla on antennal segments of male and female S. granarius have been investigated using SEM, followed by TEM. Different morphological sensilla types, including two sensilla basiconica (SB) types, with two subtypes, four sensilla coeloconica (SC) types and five sensilla chaetica (SCH) types, with one subtype, have been identified on S. granarius antennae, whose external structure and shape are peculiar. TEM micrographs of SB on the antennae of S. granarius are characterized by strongly corrugated pores around the cuticle, while micrographs of SC longitudinal sections showed flat-tipped and smooth-surfaced pegs bearing an apical pore that is suggestive of a gustatory function. TEM micrographs of SCH longitudinal sections showed dendrite branches and cuticular pore arrow heads that may be involved in the perception of humidity, temperature, heat and CO2. Because SCH of different sizes were distributed around the head and rostrum, these may function as contact-chemoreceptors .These results are discussed in relation to the possible roles of the sensilla types in the host location behavior of S. granarius.