Morphological Characterization of the Sensilla from the Antennal Flagella, Maxillary Palps, and Aculei, and Electroantennogram Responses of Anastrepha obliqua (Diptera: Tephritidae) to Host Volatiles.

Insect chemoreception is essential for locating food, selecting oviposition sites, and detecting infochemicals. In tephritid fruit flies, chemosensory perception occurs primarily through sensilla on the antennal flagella, maxillary palps, and ovipositor. Identifying these sensilla provides insights into olfaction, which may lead to improvements in insect control measures. This study describes the morphology of sensilla in Anastrepha obliqua (Macquart) using scanning electron microscopy, assesses their permeability to crystal violet and silver nitrate, and evaluates antennal electrophysiological responses (EAG) to host volatiles. Sensilla were classified into multiple types based on morphology and staining properties. The antennal flagella housed four types of sensilla (trichodea, basiconica, clavata, and coeloconica), whereas the sensory pit contained peg-like and coeloconica-like sensilla. Sensilla trichodea were silver nitrate-positive but refractory to crystal violet, whereas sensilla basiconica, clavata, and coeloconica were permeable to both stains, indicating olfactory function. Maxillary palps exhibited mechanosensory sensilla chaetica and olfactory sensilla basiconica; only sensilla basiconica were permeable to both stains. The aculeus contained bristle-like, peg-like, and campaniform sensilla, suggesting its role in mechanoreception and chemoreception. EAG recordings demonstrated that all tested volatiles elicited antennal responses, with no significant differences between sexes, except for propyl butyrate, which induced a stronger response in males. This is the first study to characterize the sensilla of the palps and ovipositor in Anastrepha species and provides a foundation for future olfactory and behavioural research.