Undersowing rutabaga (Brassica napus L.) with white clover (Trifolium repens L.) : effects on the cabbage root maggot (Delia radicum (L.)) and its parasitoid/predator (Aleochara bilineata Gyll.)

Coady, Juanita R. (1999) Undersowing rutabaga (Brassica napus L.) with white clover (Trifolium repens L.) : effects on the cabbage root maggot (Delia radicum (L.)) and its parasitoid/predator (Aleochara bilineata Gyll.). Masters thesis, Memorial University of Newfoundland.

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Abstract

The cabbage root maggot Delia radicum (L.) (Diptera: Anthomyiidae), particularly the second generation, is the most serious insect pest of rutabaga in Newfoundland. Cabbage root maggot larvae feed on the developing root and leave unsightly scars that reduce marketability. Undersowing rutabaga with white clover (Trifolium repens L. var. Sonja) was tested to determine the effects on cabbage root maggot adults, oviposition, rutabaga yield and marketability, carabid beetles and the root maggot predator/parasitoid Aleochara bilineata Gyll. (Coleoptera: Staphylinidae). -- Results of this study show that undersowing did have significant effects on the factors studied. The bare plots had more D. radicum females and eggs, A. bilineata (measured by both pitfall trapping and rate of parasitism), and some carabid species (Clivinafossor and Bembidion lampros). The undersown plots had higher total numbers of D. radicum of which most were males, and more of some carabid species (Pterostichus melanarius and Amara bifrons). There was a significant yield reduction in undersown compared to bare plots in 1997, and no rutabaga were marketable from either treatment. In 1998 when there was less pest pressure, yields were similar and a small percentage of rutabaga were marketable from both treatments. -- The rate of parasitism by A. bilineata was lower in the undersown plots, as observed by other researchers. An incubator study of fall-collected D. radicum pupae found peak D. radicum emergence occurred at 172 degree days (DD) and peak A. bilineata emergence occurred at 421 DD. above a base threshold of 4.4°C Survey collections showed that A. bilineata is present in all major growing areas of Newfoundland.

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