Comparison of sensory structures present on larval antennae and mouthparts of lepidopteran crop pests

Lepidopteran crop pests like Spodoptera litura (F.) (Lepidoptera: Noctuidae), Chilo partellus (Swinhoe) (Lepidoptera: Crambidae), Plutella xylostella (L.) (Lepidoptera: Plutellidae), and Maruca vitrata (F.) (Lepidoptera: Pyralidae) are the major constraints for crop production and productivity. They are polyphagous and feed on tobacco, millets, cruciferous crops, and leguminous crops, respectively. Sensory structures and sensory genes are the key players responsible for their preference for particular crop species. Sensory genes code for the chemoreceptors present in the dendritic membrane of the neuron, which interpret the signal perceived by the insect nervous system that is responsible for insect behavior. In this study, we examined the distribution and morphology of sensory structures present on larval antennae and mouthparts of 4 lepidopteran crop pest species using scanning electron microscopy. We found that the mouthparts of lepidopteran larvae all possess sensory structures and organs such as sensilla chaetica, sensilla basiconica, and sensilla styloconica involved in gustatory and olfactory functions. The only difference between species lies in the external appearance, position, distribution, and number of sensory organs. Sensilla chaetica alone were observed on the labrum and mandibles, whereas sensilla styloconica and sensilla chaetica were present on the labium. All 3 types of sensilla were observed on the maxilla of S. litura, C. partellus, P. xylostella, and M. vitrata with varied numbers and morphology. Mainly, sensilla basiconica were present on antennae and apical maxillary palps, which are involved in olfactory and gustatory functions, respectively. In addition, we compared the sensory gene odorant receptor co-receptor (Or83b), which is pivotal in olfactory reception, among the 4 lepidopteran species and found that Or83b is conserved, showing the ancestral relationship among the 4 species.