Daily changes in the responsiveness of taste receptors correlate with feeding behaviour in larvae of Spodoptera littoralis

Larvae of Spodoptera littoralis were monitored through the final larval stadium (6 days) for weight gain, amount eaten in bioassays and responsiveness of gustatory receptors to stimulation with sodium chloride and four concentrations of sucrose. The age of larvae within the stadium, time of day (am or pm) and interactions between these factors influenced the electrophysiological response to 0.05 M sucrose. Overall, the responsiveness of taste receptors increased in the first half of the stadium, then declined. Neural input correlated with weight gain on days 1 to 4, and with amount eaten in bioassays on days 1 to 5. This correlation between neural input and feeding behaviour indicates that the observed modulation in neural sensitivity has a causal relationship with feeding behaviour. The ways in which the modulation might occur are discussed.