Effect of Within-Crop Diversity on Colonization by Pest Insects

S. Finch and R.H. Collier

Abstract
Cauliflower host plants were surrounded by three species of marigold (Tagetes spp.) and five other species of aromatic plants to determine whether aromatic plants were more effective than non-aromatic plants at disrupting egg-laying by pest insects.

The “model” test insect was the cabbage root fly (Delia radicum) and the non-aromatic plants tested included common garden bedding plants and weeds.

Of the 24 plant species tested, 20 disrupted egg-laying by the fly. Aromatic plants were no more disruptive than non-aromatic plants. The disruptive effect varied from one plant species to another and depended upon the architecture of the nonhost plants.

In the current tests, the least disruptive plant was common fumitory (36% reduction in egg numbers) and the most disruptive was fat hen (82% reduction). Plants of cineraria, alyssum and lobelia, that appeared grey, white and blue, respectively, were not disruptive.

To be disruptive the non-host plants must be close to the cauliflower plants, equivalent to growing in the “within row” area, and be green.

Contrary to popular belief, the pungent chemicals found in aromatic plants did not deter the pest insects from landing or repel them after landing. The disruption by all non-host plants is caused simply by the presence of additional green surfaces.


Source
British Grassland Society, 2004 Symposium No. 37, "Organic Farming: Science and Practice for Profitable Livestock and Cropping" Proceedings
Association of Applied Biologist & Colloquium of Organic Researchers


Author Locations and Affiliations
Horticulture Research International, Wellesbourne, Warwick, CV35 9EF, UK


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Posted January 2008