PARENT SESSION
Contributed Oral Session 8: Invertebrate Ecology: Butterflies; Soil Insects
Monday, August 8, 8:00 AM - 11:30 AM, Meeting Room 518 C, Level 5, Palais des congrès de Montréal
What lies beneath: How do soil insects find host plant roots?
Johnson, Scott*,1, Gregory, Peter1, Zhang, Xiaoxian2, 1 Scottish Crop Research Institute, Dundee, United Kingdom2 University of Abertay, Dundee, United Kingdom
ABSTRACT- A range of insect herbivores have soil-dwelling stages that feed on plant roots, yet comparatively less is known about the belowground aspects of their ecology than aboveground stages. Our research focused on the clover root weevil (Sitona lepidus), which attacks white clover (Trifolium repens) throughout Europe and the USA. The adult weevil 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. Using soil filled Y-tubes we found that newly hatched S. lepidus larvae were able to distinguish white clover roots from less suitable non-host plants such as ryegrass, strawberry clover and sub-clover. Furthermore, the novel use of X-ray tomography 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 nature of the mechanism underpinning host plant attraction and preference 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, but their searching efficiency significantly increased at higher CO2 concentrations. Movement patterns at higher CO2 concentrations ensured that larvae visited more new sites and fewer previously visited sites than if moving in a random fashion. 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.
Key words: Sitona, Levy walks, Carbon dioxide, Flavonoids