PARENT SESSION
Oral Session # 41: Herbivory III: Forests and Soils.
Presiding: R Jones
Wednesday, August 6. 8:00 AM to 11:30 AM, SITCC Meeting Room 103.
Root weevil attraction to clover roots − the roles of general and specific signals.
Johnson, Scott*,1, Gregory, Peter1, 1 University of Reading, Reading, United Kingdom, United Kingdom
ABSTRACT- The clover root weevil (Sitona lepidus) exclusively attacks white clover (Trifolium repens) throughout Europe and North America, where it is valued both as a forage legume and for the nitrogen enrichment it provides to grassland. The adult weevil feeds on leaves above-ground where it lays eggs that fall to the soil surface. Soil-dwelling larvae emerge from eggs and feed on roots, initially feeding on root nodules containing the N2 fixing rhizobia, before feeding on progressively larger roots. Using X-ray microtomography we have shown that newly-hatched larvae move to the root nodules directly. We tested the hypothesis that chemical signals from the roots or root rhizobial nodules could be exploited by S. lepidus to locate white clover roots. In arena experiments, >85% of responsive S. lepidus selected host plant roots (T. repens) over non-host plant roots (e.g. ryegrass, red clover, vetch). When given a choice between T. repens roots with and without root nodules, 60% of responding insects selected roots with nodules and 40% chose those without. In choice tests between T. repens roots and excised root nodules, >80% of responsive S. lepidus selected non-nodulated roots rather than the excised root nodules. Respiratory emissions of CO2 from roots are known to attract some root feeding insects. S. lepidus showed a dose-dependent attraction to CO2 in arena experiments. CO2 concentrations in the rhizosphere of T. repens with root nodules were >20% higher than the rhizosphere of T. repens without root nodules, and >30% higher than the rhizosphere of non-host plants. It is proposed that specific chemical signal(s) are implicated in the attraction of S. lepidus to T. repens roots, but general signals, such as CO2, might also play a role in root location.
Key words: soil insect, x-ray microtomography, chemical ecology, Sitona lepidus