Wireworms (Coleoptera: Elateridae) Use Root Volatiles and CO2 to Discriminate Among Host Plants.

In the absence of visual signals, subterranean arthropods rely on olfactory and tactile cues to navigate toward resources. Here, in a series of pairwise dual-choice bioassays, we investigated the Limonius californicus (Col., Elateridae) larva response to wheat, pea, and bean seedlings in sand-filled olfactometers. We then quantified volatile organic compounds (VOC) emitted from roots. Wireworm preference for beans compared to wheat was attributed to the higher CO2 emission. Wireworm preference for peas compared to wheat was attributed to the higher amounts (µg/hr) of hexanal emitted from pea roots. Wireworms preferred synthetic hexanal over clean air control and the higher amount of hexanal (200 µg) over the lower amount of 20 µg. In the presence of CO2 at both ends of the olfactometer, wireworms did not respond preferentially toward hexanal. 2-Hexenal was also attractive to wireworms relative to the control, but wireworms did not discriminate between hexanal and 2-hexenal. While our results confirmed wireworms' positive response to the presence of CO2 and some VOCs in isolation, their host choice appears to be driven by the combination and the concentrations of the present cues, allowing the insect to distinguish among host plants.