Report on the Types and Distribution of Antennal Sensilla of the Phytophagous Leaf Beetle, Chrysochus Chinensis (Coleoptera: Eumolpidae) and their Putative Functions

Chrysochus chinensis (Baly) (Chrysomelidae: Eumolpinae) is a medium-sized phytophagous leaf beetle and have complicated diets. This beetle searches for host plants with its sensory system. To further explore the mechanisms of host location and to understand the ultrastructure of C. chinensis, we examined the morphology and distribution of its sensilla on the antennae and mouthparts of male and female adults, using scanning electron microscopy (SEM). Both male and female antennae are filiform and can be divided into scape, pedicel, and flagellum. There were four types and eight subtypes of antennal sensilla, including two subtypes of sensilla chaetica (SC1, SC2), three subtypes of sensilla basiconica (SB1, SB2, SB3), two subtypes of sensilla trichoidea (ST1, ST2) and Böhm's bristles (BB). No sexual dimorphism in sensilla type was observed, but there were variations between males and females in the numbers and distribution along the antennae. SC1 and SC2 were absent from the scape and pedicel. SB1, SB2 and SB3 were found only on the last 5 segments of the antennae and were absent on the first 6 segments in both sexes. ST1 and ST2 occurred on all antennal segments in both sexes. BB only occurred on the scape and pedicel. The distal antennal sensilla of C. chinensis had notably more sensilla than proximal ones in type and number, indicating this is the main area to detect environmental stimuli for feeding or oviposition. We discussed potential function related to structure via comparisons with previous investigations of Coleopteran and other insects. Our results provide a theoretical basis for further studies on sensory physiological function.