Evaluating the enemies hypothesis in a clover‐cabbage intercrop: effects of generalist and specialist natural enemies on the turnip root fly (Delia floralis) |
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Authors: | Maria Björkman Peter A. Hambäck Richard J. Hopkins Birgitta Rämert |
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Affiliation: | 1. Department of Crop Production Ecology, Swedish University of Agricultural Sciences (SLU), PO Box 7043, SE‐750 07 Uppsala;2. Present address: Bioforsk, Norwegian Institute for Agricultural and Environmental Research, Plant Health and Plant Protection Division, Department of Entomology and Nematology, H?gskoleveien 7, 1432 ?s, Norway.;3. Department of Botany, Stockholm University, SE 106 91 Stockholm;4. Department of Ecology, Swedish University of Agricultural Sciences, PO Box 7047, SE 750 07 Uppsala;5. Department of Plant Protection Biology, Swedish University of Agricultural Sciences, PO Box 44, SE 230 53 Alnarp, Sweden |
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Abstract: | - 1 The relative importance of the resource concentration hypothesis and the enemies hypothesis was investigated for the turnip root fly Delia floralis in a cabbage–red clover intercropping system compared with a cabbage monoculture.
- 2 Delia floralis egg densities were measured as well as the activity‐densities of generalist predators in a field experiment during two growing seasons. In the second year, a study of egg predation with artificially placed eggs was conducted, in addition to a predator exclusion experiment, to estimate total predation during the season. Parasitization rates were estimated from samples of pupae.
- 3 Delia floralis oviposition was greater in the monoculture during both years. The predator activity‐densities differed between treatments and study years. The known natural enemies of Delia spp., Bembidion spp. and Aleochara bipustulata showed a strong response to a cultivation system with higher activity‐densities in the monoculture. The response, however, appeared to be caused primarily by habitat preferences and not by D. floralis egg densities.
- 4 The reduction in the number of D. floralis pupae in the intercropping may be explained by a disruption in oviposition behaviour caused by the presence of clover because neither predation, nor parasitization rates differed between cultivation systems.
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Keywords: | Delia radicum natural enemies hypothesis parasitization predation resource concentration hypothesis |
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