Morphological and electrophysiological analysis of tarsal sensilla in the medfly Ceratitis capitata (Wiedemann, 1824) (Diptera: Tephritidae)

Abstract The Mediterranean fruit fly, Ceratitis capitata (Wiedemann, 1824) (Diptera: Tephritidae), is a polyphagous pest in horticulture, mainly targeting pomaceous and citrus fruits. To gain better knowledge about its chemosensory system related to taste, essential for behavioural strategies and localisation of host plants, we examined the tarsal external morphology by high-resolution scanning electron microscopy, focusing on sensilla. Numerous trichoid and chaetica sensilla, related to taste and mechanoreceptor systems, and other types of sensilla are present in tarsal segments. The responses of specific trichoid chemosensilla were also studied through electrophysiological experiments by stimulation with sodium chloride, fructose and four bitter stimuli. Electrophysiological data allowed us to distinguish three types of different neurons: high (“H”), middle (“M”) and small (“S”). Increasing concentrations of sodium chloride enhanced the activity of H cells, while fructose boosted M cells activity. On the contrary, S cells showed no increase in spike activity after stimulation with these substances. Bitter stimuli induced no significant response on these cells. Behavioural assays showed no statistical difference among the responses to sugars, bitter substances and citric acid. Our results on taste stimuli will be useful in increasing knowledge of Ceratitis chemoreception, fundamental in new integrated pest management.