Microstructure of mandibulate mouthparts in the greater rice weevil, S itophilus zeamais ( C oleoptera: C urculionidae)

The greater rice weevil, Sitophilus zeamais, is a serious pest of stored grain. It chews a hole in the grain and deposits an egg inside. For the purpose of excavating a tunnel, these weevils are equipped with effective mandibulate mouthparts for penetrating and boring holes. The mouthparts of the weevil are a long slender snout, which consist of a labrum, a pair of mandibles, a pair of maxillae and a labium. Mothparts exhibit typical morphology of phytophagous coleopteran beetles and have characteristics of chewing mouthparts. Mandibles are connected to the head capsule through dicondyous articulation, which allows movement along one single rotating axis. Both labrum and labium are fused to the snout and form the upper and lower lips, respectively. Along the depressed surface of the snout, a number of short sensory hairs are sparsely arranged. The distal apexes of the maxillary and labial palpi are deeply depressed into a sensillar field, and only one type of the basiconic sensilla, which function as chemo‐ or gustatory receptors, occurs in both sexes.