By: Mervat A. Seada

Entomology Division, Department of Zoology, Tanta University, 31527-Tanta, El-Gharbiya, Egypt.

Abstract

The gustatory system in insects is composed of detectors screening different panels of ligands, which enable or suppress life behaviors depending on the context. Single sensillum electrophysiology recordings were conducted from the antennal sensilla chaetica of an adult female moth of Spodoptera littoralis to ascertain whether these sensilla have a gustatory function. Five test stimuli (NaCl, sucrose, ethanol, green cotton leaves extract, and conspecific larval frass extract) were used to stimulate each sensillum. Two types of gustatory sensilla chaetica located on the same flagellomere of the distal third of the antenna were characterized, each sensillum enclosed three gustatory receptor neurons (N1, N2, and N3). Overall, responses (spikes/s) were higher in the case of low concentration of sucrose and higher concentration of ethanol than of salt and higher concentration of sucrose. Individual differences were observed in the response patterns of these sensilla to the tested stimuli but functional sensillum types could not be identified. Higher concentrations of sucrose, ethanol extracts of green cotton leaves, or conspecific larval frass significantly stimulated the same neuron of ventral and lateral sensilla chaetica. Response patterns revealed that antennal gustatory sensilla contain gustatory neurons, which are possible receptors for host-plant recognition. Moreover, stimulation of the female’s antennae with phagostimulative sucrose evoked activation of the proboscis extension reflex with dose-dependent responses. Differences in sensilla distribution and their response patterns suggest that gustatory sensilla on the antennae of the female S. littoralis have a key role in adaptation and host plant recognition.

Preliminary observations of the gustatory function of sensilla on antennae of the female Spodoptera littoralis Lepidoptera Noctuidae from single compounds to complex natural stimuli

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