Spatial odor discrimination in the hawkmoth, Manduca sexta (L.)

Abstract

Flying insects track turbulent odor plumes to find mates, food and egg-laying sites. To maintain contact with the plume, insects are thought to adapt their flight control according to the distribution of odor in the plume using the timing of odor onsets and intervals between odor encounters. Although timing cues are important, few studies have addressed whether insects are capable of deriving spatial information about odor distribution from bilateral comparisons between their antennae in flight. The proboscis extension reflex (PER) associative learning protocol, originally developed to study odor learning in honeybees, was used as a tool to ask if hawkmoths, Manduca sexta, can discriminate between odor stimuli arriving on either antenna. We show moths discriminated the odor arrival side with an accuracy of >70%. Information about spatial distribution of odor stimuli may be available to moths searching for odor sources, opening the possibility that they use both spatial and temporal odor information.This article has an associated First Person interview with the first author of the paper.

Keywords: Odor localization; Olfaction.

Fig. 1.

Behavioral setup and training protocol. (A) Schematic diagram of behavioral setup showing a restrained moth with its straightened proboscis and odor delivery onto its antennae. Reward delivery port was placed at the distal tip of the proboscis. The feeding response was monitored using EMG activity of the suction pump muscles in the head. (B) Schematic diagram shows events during training and test protocols. Odor was presented for 5 s and 3 s after odor onset the reward valve was activated for 0.1 s. Moths were not rewarded during test session.

Fig. 2.

Odor-arrival side discrimination response. Pie charts show the number of moths that learned the odor- arrival side task for both linalool (A) and benzaldehyde (D). Bar graphs showing EMG % response for both left (blue bar) and right (red bar) side odor delivery. Panels B and E show the moths’ response when their left antenna was conditioned, and panels C and F when their right antenna was conditioned. (B,C) Moths discriminated linalool arrival side. Response to the associated side was higher, >70% compared to the unassociated side, <30%. (C) Moths discriminated benzaldehyde arrival side. Response to the associated side was higher, >70% compared to the unassociated side, <25%. (B,C,E and F) Error bars indicate standard error of mean.