The effects of three plant acids on the gustatory response of Manduca
sexta larvae were examined. Two different categories of response were
recorded in the styloconic sensilla of different individuals in the pr
esence of salt: the gustatory response to salt was reduced especially
at the lower pHs; the deterrent cell fired particularly at the lower p
Hs. In some individuals neither response was seen except at the lowest
pHs. Additional experiments indicated that the effect was due to pH a
nd not to specific effects of any of the acids. Ascorbic acid was test
ed with the nutrient carbohydrates glucose and inositol, and was found
consistently to reduce the gustatory responses to these compounds. Th
e data indicate that plant acids at natural concentrations could influ
ence food acceptability.