Intercropping as a management strategy against carrot rust fly (Diptera: Psilidae): a test of enemies and resource concentration hypotheses
Ramert, B. | Ekbom, B.
Intercropping with lucerne, Medicago littoralis Rohne ex. Loisel, as a management strategy for carrot rust fly, Psila rosae (F.), was studied to understand why intercropping results in lower damage. Densities of polyphagous predators were experimentally enhanced and decreased using ingress and egress plots. The manipulation method was successful for carabids and for spiders in the family Lycosidae and the order Opiliones. The method was less effective for staphylinids and linyphiid spiders. These results are discussed in relation to carrot rust fly damage and earlier experiments with abundance of polyphagous predators in carrots, Daucus carota L., in monoculture and intercrop. In field experiments, D-vac catches were used to measure the number of flies in 2 treatments arranged in 3 different ways. More flies were caught in the monoculture treatment when plots were placed next to each other or placed apart from each other and surrounded with ley (i.e., nonhost) vegetation, but no difference was found between treatments when plots were surrounded by bare soil. In greenhouse experiments, egg deposition was lower in intercropping. These results are discussed in relation to damage levels, which were always lower in intercropping. We also discuss our results with regard to the possible outcome of scaling up our small plot experiments to full scale cropping practices.
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