Gustatory perception and feeding preference of Spodoptera frugiperda (Lepidoptera: Noctuidae) larvae to four stimuli.
Aim: The aim of this study is to screen effective phagostimulants and deterrents, and to explore the gustatory perception mechanism of Spodoptera frugiperda larvae, so as to provide theoretical and practical references for the ecological control of the pest. Methods: The single sensillum recording technique was used to investigate the electrophysiological characteristics of the medial sensillum styloconicum and the lateral sensillum styloconicum located on the maxillary galea of mouthparts of the day-2 5th instar larvae to four stimuli of sucrose, sinigrin, tannic acid, and quinine hydrochloride at different concentrations. The two-choice feeding assay was used to investigate the feeding choice of S. frugiperda larvae to these stimuli. Results: Both the medial sensillum styloconicum and the lateral sensillum styloconicum of S. frugiperda larvae consist of gustatory receptor neurons sensitive to sucrose, sinigrin and tannic, with the responding activities of neurons changing based on stimuli and concentrations. However, the quinine hydrochloride only elicited electrophysiological responses of the medial sensillum styloconicum but not the lateral sensillum styloconicum. The responses of gustatory receptor neurons in both the medial and lateral sensilla styloconica to sucrose and sinigrin showed typical dose-dependent patterns, while the response of quinine hydrochloride to the medial sensillum styloconicum showed a reverse dose-dependent pattern. The results of behavioral choice showed that sucrose significantly induced the feeding choice of S. frugiperda larvae, while sinigrin, tannic and quinine hydrochloride inhibited their feeding choice in a dose-dependent pattern. Conclusion: Gustatory receptor neurons housed in both the medial and lateral sensilla styloconica of S. frugiperda larvae respond to phagostimulants and deterrents. The two types of sensilla demonstrate different responding patterns in response spectrum and responding activities. Sucrose can be regarded as one candidate compound of phagostimulants, while quinine hydrochloride, sinigrin and tannic acid can be regarded as the candidate compounds of deterrents. The gustatory responding profiles of larvae may contribute to determining their feeding preference for these compounds. This study provides gustatory information for the ecological control of S. frugiperda.