Sugar beet wireworm (Limonius californicus (Coleoptera: Elateridae)) host preference: Quantifying wireworm response to CO2 and root volatiles

Wireworms are the larval stage of click beetles (Coleoptera: Elateridae), and several of their species are pests of various crops. Wireworms are soil-dwelling and use cues such as CO₂ and root volatiles to find their hosts. However, there is limited information available on the roles of specific volatile compounds and their concentrations, alone or in combination with CO₂, in wireworm host preference. Focusing on the late instar of the sugar beet wireworm, Limonius californicus, we first examined wireworm preference for wheat, pea and bean seedlings, in a series of pairwise choice bioassays. CO₂ and volatile organic compounds released from intact seedling roots were also quantified. Wireworms preferred bean seedlings over wheat and pea, and they preferred pea versus wheat seedlings. CO₂ concentration in the bean root rhizosphere was significantly higher than either pea or wheat. Hexanal was the most abundant volatile in seedling rhizospheres and its concentrations differed among the three host plants, with the highest concentration detected in pea. In pairwise choice bioassays, wireworms preferred hexanal, administered in a triacetin solution at the two concentrations of 20 and 200 µg over the triacetin-only control. Wireworm response was also determined to be influenced by hexanal concentration as they preferred 200 over 20 µg. Wireworm responses to combinations of volatile compounds and CO₂ are being investigated and results will be presented. Identifying cues that wireworms use to select their hosts is important for developing plants that are less attractive to these pests or for identifying and developing effective trap crops.