Abstract
Interactions between belowground and aboveground heterotrophic communities with no direct physical contact can be connected by the plant as a mediator. Plants respond to the attack of herbivores by producing a suite of defensive compounds that can affect the choice and performance of other herbivores. The aim of this study was to determine the impact of one herbivore's activity on the acceptability of that plant to another species of herbivore. Two herbivores were tested; root-knot nematode, Meloidogyne incognita (RKN), a belowground plantparasitic nematode, and the two-spotted spider mite, Tetranychus urticae (TSSM), an aboveground folivore. We conducted herbivore preference and performance tests on Lima bean (LB) (Phaseolus lunatus cv. Henderson) as an optimal host for TSSM, and tomato (Solanum lycopersicum cv. Rutgers) which is a sub-optimal host for TSSM but optimal host for RKN. We used two-choice glass olfactometers to measure the response of RKN to plants that were exposed to TSSM versus a clean LB plant. RKN infected the clean plants at a significantly greater rate than the TSSM exposed plants. TSSM preference was measured, using leaf discs and two-choice olfactometers containing a RKN infected plant versus a clean plant at different days post-inoculation (DPI) of the RKN. TSSM preferred the clean plants to those with 25-day old RKN infections on LB, but preferred RKN infected tomato plants at 1 DPI. We also tested the effect of the inoculation (1 DPI) of the entomopathogenic nematode (EPN) Steinernema carpocapsae on tomato plants and TSSM preferred the EPN inoculated plants. We carried out a non-choice performance test for TSSM on both LB and tomato on plants inoculated with RKN versus clean plants and observed no effect of RKN exposure on TSSM performance. This research shows that plants can mediate interactions between below and aboveground herbivores that share the same plant.