Fine Structure and Sensory Apparatus of the Mouthparts of the Maize Weevil,Sitophilus zeamaisMotschulsky (Coleoptera: Curculionoidea: Dryophthoridae)

Abstract

The maize weevil Sitophilus zeamais Motschulsky is one of the most serious stored-product pests worldwide. It causes significant damage and major post-harvest losses in global production as a result of adults and larvae feeding on stored grains and contaminating food products. The fine structural morphology of mouthparts, including the distribution of sensilla in adult S. zeamais , was observed using a scanning electron microscope. The mandibulate mouthparts are situated at the tip of the long rostrum. The sclerotized mandibles are irregular, serving as pincers. The maxillae are bilaterally flattened and lay almost perpendicular to the segmented venter, situated in longitudinal clefts with a four-segmented palp on each side of the labium. The cardo, stipes, palpifer, lacinia, and galea are described in detail. The tongue-like labium is considerably specialized with a pair of three-segmented palps. Four types of sensilla basiconica occur in the distal cavity of the maxillary palp and digitiform sensilla are located on the distal maxillary segment. Two types of sensilla basiconica with a 4 + 3 arrangement are present in the distal cavity of the labial palp, whereas a kind of sensilla basiconica is present at the base of the labial palp. The evolution of the mouthpart morphology and the putative functional significance of their sensilla are discussed, providing insight into the feeding mechanism.