A mannitol/sorbitol receptor stimulates dietary intake in Tribolium castaneum

Abstract

Perception of chemical stimuli by insects aids in accepting or rejecting food. Gustatory receptors (Grs) regulating external signals in chemosensory organs have been found in many insects. Tribolium castaneum, a major pest of stored products, possesses over 200 Gr genes. An expanded repertoire of Gr genes appears to be required for diet recognition in generalist feeders; however, it remains unclear whether T. castaneum recognizes a suite of chemicals common to many products or whether it is attracted to specific chemicals, and whether its Grs are involved in its feeding behavior. It is difficult to determine the food preference of T. castaneum based on its dietary intake due to a lack of appropriate methodology. This study established a novel dietary intake estimation method using gypsum, designated the TribUTE (Tribolium Urges To Eat) assay. T. castaneum adults were fed gypsum block without added organic compounds. Sugar preference was determined by adding sweeteners and measuring the amount of gypsum in the excreta. Mannitol was the strongest attractant of T. castaneum dietary intake; in addition, TcGr20 was responsible for mannitol and sorbitol responses in Xenopus oocyte expression, but did not respond to any other non-volatile compounds tested. The EC50 values of TcGr20 for mannitol and sorbitol were 72.6 mM and 90.6 mM, respectively, suggesting that TcGr20 is a feasible receptor for the recognition of mannitol in lower concentrations. TcGr20 was expressed in the antennae, where the perception of mannitol would occur. We examined whether TcGr20 was involved in mannitol recognition using RNAi and the TribUTE assay. The amounts of excreta in TcGr20 dsRNA-injected adults decreased significantly despite the presence of mannitol, compared to that of the control adults. Taken together, our results suggest that T. castaneum adults recognized mannitol/sorbitol using TcGr20 receptors, thereby facilitating their dietary intake.\n\nAbbreviation