Tuesday, August 7, 2007 - 1:50 PMOOS 16-2: Grazing in the dark: The chemical ecology of root-feeding insects
Scott N. Johnson, Scottish Crop Research Institute
A number of insect herbivores have soil-dwelling life-stages that feed on plant roots, yet comparatively less is known about the belowground aspects of their chemical ecology than aboveground stages. This presentation will use the clover root weevil (Sitona lepidus), which attacks white clover (Trifolium repens) as a model system. The adult feeds on leaves aboveground where it lays eggs that fall to the soil surface. Soil-dwelling larvae emerge from eggs and feed on roots, normally feeding on root nodules containing the N2 fixing rhizobia, before moving on to progressively larger roots. The novel use of X-ray tomography has allowed us to non-invasively observe newly hatched larvae approaching and attacking the white clover roots, and in particular the root nodules. When given a choice between N2-fixing root nodules and inactive (non N2-fixing) nodules, larvae strongly preferred the N2-fixing nodules. The mechanism underpinning host plant attraction was investigated. In contrast to several other studies that suggest root emissions of CO2 attract soil-dwelling insects, S. lepidus larvae were not attracted to CO2 per se, but their searching behaviour intensified at higher CO2 concentrations. A range of compounds in white clover roots and root nodules were quantified and subsequently screened for behavioural activity with larvae. Sitona lepidus larvae were attracted to an identified flavonoid compound that was particularly abundant in N2-fixing root nodules.