Abstract
Many animals rely on chemical cues to recognize and locate a resource, and they must extract the relevant information from a complex and changing odor environment. For example, in moths, finding a mate is mediated by a sex pheromone, which is detected in a rich environment of volatile plant compounds. Here, we investigated the effects of a volatile plant background on the walking response of male Spodoptera littoralis to the female pheromone. Males were stimulated by combining pheromone with one of three plant compounds, and their walking paths were recorded with a locomotion compensator and analyzed. We found that the addition of certain volatile plant compounds disturbed the orientation toward the sex pheromone. The effect on locomotion was correlated with the capacity of the plant compound to antagonize pheromone detection by olfactory receptor neurons, suggesting a masking effect of the background over the pheromone signal. Moths were more sensitive to changes in background compared to a constant background, suggesting that a background odor also acts as a distracting stimulus. Our experiments show that the effects of odorant background on insect responses to chemical signals are complex and cannot be explained by a single mechanism.
Highlights
Insects rely largely on chemical cues to recognize and locate essential resources
We previously showed that backgrounds of linalool and some other PVs reduce the responses of olfactory receptor neurons tuned to pheromone components (Ph-ORNs) [18], while preserving the temporal coding of pheromone pulses [20] in male S. littoralis
At the dilution used for background in the electrophysiology and behavioral experiments (0.1%), the EAG amplitudes for Lin (1.23 mV) and for Hex:Ac (0.54 mV) were significantly higher than the responses to mineral oil, (Wilcoxon signed rank test, P = 0.002, N = 13 for Lin and P = 0.003, N = 17 for Hex:Ac)
Summary
Insects rely largely on chemical cues to recognize and locate essential resources Their olfactory system must extract the relevant information from a complex and changing odor environment. With the varying amount of volatiles produced by individual plants and a highly variable combination of different plants in their natural habitats, the olfactory environment of a moth is complex and continuously changing. In presence of 0.1% Lin, the number of spikes emitted during the Phero stimulation was reduced (Wilcoxon signed rank test, P = 0.052). Between Phero stimulations, Ph-ORNs emitted 1.360.7 spikes in Lin 0.1% vs 3.160.8 in a neutral background. This difference was not significant (Wilcoxon signed rank test, P = 0.1)
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