Porthetria dispar larvae were fed sucrose solutions of different concns. Water was used as a control. The taste threshold for sucrose is .1M. The dextrose threshold is .5M. The HCl threshold is .05M. Larvae of Anosia plexippus, Papilio polyxenes, Diacrisia virginica, Estigmene acraea, Samia cecropia, Isia isabella, and Euchaetias egle have the same thresholds. External temp., age of larvae, and fatigue of end organs do not appear to affect the thresholds. The olfactory threshold of E. egle larvae for ethyl alcohol is 55 mg./liter. The organs for taste are located in the epi- and hypopharynx. and olfactory organs are located in the antennae and maxillae. The primary factors influencing food plant choice by larvae are taste and smell.