Ultramorphological differentiation of mouthparts and sensilla in Chilocorus rubidus (Coleoptera: Coccinellidae): From larva to adult and functional implications.

As holometabolous insects, ladybird beetles display marked morphological differences between the larval and adult stages. However, the larvae and adults of Chilocorus rubidus share the same diet, and no prior study has compared their mouthparts. In this study, scanning electron microscopy (SEM) was used to examine the ultramorphology of mouthparts and associated sensilla in both adults and larvae of C. rubidus. The results showed that the mouthparts of C. rubidus are of the typical biting-chewing type, and their basic composition of the mouthparts are conserved between larvae and adults. However, the specific morphological characteristics of each mouthpart component varies among different larval instars and between larvae and adults, particularly from the 4th instar to the adult stage. The mandibles of larvae bear bifid incisors, whereas those of adults are unidentate. Additionally, the maxilla and labium exhibit distinct structural differences between the two stages. Six types of sensilla and two types of glandular structures were identified on the adult mouthparts, among which sensilla campaniformia (Sca), sensilla coleconica (Sco), perforated plates (Pp), and cuticular pores (Cp) were absent in the larval stage. The number of all sensillum types gradually increased from the larval to adult stage, especially for the sensory fields on the top of labial palpi and maxillary palpi. In particular, sensilla styloconica II are observed on the tip of labial palpi of ladybird beetles for the first time. These results provide a theoretical basis for understanding the biological control potential of this species.