CHANGES IN THE RESPONSIVENESS OF THE MAXILLARY STYLOCONIC SENSILLA OF SPODOPTERA-LITTORALIS TO INOSITOL AND SINIGRIN CORRELATE WITH FEEDING-BEHAVIOR DURING THE FINAL LARVAL STADIUM

An electrophysiological and behavioural study showed that the responsiveness of Spodoptera littoralis (Boisduval) larvae to inositol and sinigrin varied within the final stadium. The insects were reared on a bean-based artificial diet and larvae were removed twice daily for experiments, morning and afternoon, throughout the final stadium. The lateral and medial maxillary styloconic sensilla of one subset of larvae were stimulated sequentially three times with inositol and sinigrin. The other subset were exposed, for 4 h, to glass-fibre discs treated with either inositol or sinigrin and the amount eaten recorded. The response of the lateral maxillary styloconic sensillum to inositol was correlated with the amount eaten of inositol-treated glass-fibre discs. The response of the lateral sensillum increased during the first 4 days of the stadium then declined the response of the sensillum was greater in the morning than in the afternoon. The amount eaten of sinigrin-treated glass-fibre discs was correlated with the response of the medial sensillum to sinigrin, the neural response increased over the first 3 days of the stadium, and was greater in the afternoon than the morning. The variability in neural activity has important implications in the study of neural coding.