Morphology and ultrastructure of chemosensory sensilla of labiomaxillary complex in the Colorado potato beetle, Leptinotarsa decemlineata (Col.: Chrysomelidae), larvae

The Colorado potato beetle, Leptinotarsa decemlineata (Say), is a destructive insect pest of potato and other solanaceous crops. The type, number and distribution of sensory receptors on the labio-maxillary complex of larvae were studied using the scanning and transmission electron microscopy. A total of 32 sensilla were identified on the maxillary and labial palps that were categorized in three basic morphological types: basiconica, trichoid, and digitiform. The maxillary palp had 16 basiconica, four trichoid and one digitiform sensilla, and the labial palp included 11 basiconica sensilla. All basiconica sensilla were on the distal apex of the palp segment. The basiconica sensilla are innervated by 2-6 neurons and function as a gustatory receptor. In addition, three trichoid sensilla were on the distal side of the second segment, one trichoid sensillum on the lateral side of the third segment and one digitiform sensillum on the lateral side of the third segment of maxillary palp. Trichoid sensilla are equipped with 4-6 receptor cells and function as chemo- and mechanoreceptors.