Associative olfactory learning in the moth Manduca sexta

The proboscis extension response conditioning protocol has been used to explore olfactory-based associative learning in an array of insects. We have monitored a different feeding reflex, which involves activation of the cibarial pump, to demonstrate olfactory learning in the moth Manduca sexta. In the first experiment, four different treatment conditions were used to assess associative (Pavlovian) learning. The results indicate that an excitatory cibarial pump response develops and is retained for at least 24 h only when odor is forward-paired with the presentation of sucrose. Three control treatments, backward pairing, air (no odor) pairing and random pairing, failed to increase the cibarial pump response. However, an excitatory cibarial pump response developed when the backward- and air-paired groups received forward pairing of odor and sucrose on the following day. In contrast, moths experiencing random pairing on day 1 displayed a slower rate of acquisition during forward pairing on day 2, which may indicate inhibition. The second experiment investigated discrimination learning. Two odors were randomly presented, one odor being forward-paired with sucrose (+), the other presented alone (-) in a counterbalanced design. Again, only when odor was forward-paired with sucrose did learning occur. We discuss the implication of these findings for a broader comparative analysis of learning in insects.