Morphology of Mouthparts and Distribution of Sensilla in Immature Stages and Adults of Parthenium Beetles

The Parthenium beetle, Zygogramma bicolorata Pallister (Coleoptera: Chrysomelidae) is a notable biocontrol agent against invasive Parthenium weed in Australia, South Africa, and the Indian subcontinent. While larvae consume both inflorescences and leaves, and adults feed exclusively on leaves, no prior study has compared the mouthparts of Z. bicolorata larvae and adults. Present study utilized scanning electron microscopy to investigate the morphology and distribution of sensilla on mouthparts of fourth-instar larvae, pupae, and adults. Our results revealed that fourth-instar larvae had 9-different sensillum types: sensilla chaetica (Sch I-III), sensilla basiconica (Sb I-V), and sensilla digitiformia (Ds) on their mouthparts, whereas pupal sensilla were fewer and less distinct. In adults, 13-different sensillum types were present: sensilla chaetica (Sch I-III) on labrum, labium, mandibles, and maxillae; sensilla basiconica (Sb I-VI) on labium, epipharyx, lacinia, maxillary palps, and labial palps; sensilla digitiformia (Ds) on maxillary palps; and sensilla campaniformia (Sca), and sensilla coeloconica (Sco I-II) on epipharyx. These sensilla likely play vital roles in feeding behavior, sensory perception, and host plant detection. Our findings provide a microscopic morphological foundation for further research on food recognition mechanisms and local adaptations in specialist phytophagous insects.