A simple approach to evaluate behavioral responses of insect herbivores to olfactory and visual cues simultaneously: the double stacked y-tube device and portable volatile collection system

Abstract

Insect herbivores use olfactory and visual cues during host plant finding. Although insect responses to these cues typically are assessed separately, in nature herbivores respond to olfactory and visual cues simultaneously. We demonstrate the functionality of a “double-stacked y-tube device” (D-SYD) to measure bioassay responses of a specialist herbivore to olfactory and visual cues of potential host plants either presented individually or in combination. We tested the ability of the Eurasian specialist seed-feeding weevil, Mogulones borraginis, to distinguish between its Eurasian host, Cynoglossum officinale, which is invasive in North America, and a closely related confamilial native North American non-target, Andersonglossum occidentale. Weevils distinguished C. officinale from A. occidentale based on olfactory and visual cues. When olfactory and visual cues were offered simultaneously, weevils preferentially selected C. officinale more strongly and more rapidly than when either single cue was offered. When olfactory and visual cues were mismatched, weevils were no longer able to discriminate between the plant species and exhibited longer response times. There were no differences in behavioral responses to floral scents from greenhouse-propagated plants and those collected from plants in the field using a portable volatile collection system (PVCS). The bioassay approach demonstrated here using D-SYD and PVCS can assess behavioral responses of insects to olfactory and visual plant cues alone or together and measure their relative contributions to host discrimination. This will have utility for theoretical and applied questions concerning the host selection behavior of insect herbivores.