Managing the cabbage maggot, Delia radicum (L.), by means of agroecosystem diversification

Parsons, Carolyn K. (2010) Managing the cabbage maggot, Delia radicum (L.), by means of agroecosystem diversification. Doctoral (PhD) thesis, Memorial University of Newfoundland.

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Abstract

The cabbage maggot, Delia radicum (L.) (Diptera: Anthomyiidae) is the most serious pest of brassica crops in the temperate world. Increasing plant diversity in an agricultural system can reduce cabbage maggot oviposition due to a disruption in the host plant finding behaviour. Diversification can be accomplished several ways including intercropping and undersowing. Competition between component crops in the field has been an impediment to the adoption of diversification as a management tool for cabbage maggot. The current research investigated the disruptive potential of several plant species and the effect of two different types of habitat diversification on reducing cabbage maggot oviposition while minimizing competition. Effects on the sympatric species, Delia platura and D. florilega also were examined and species compositions compared to available data from the 1950s. -- Results of cage studies testing different plant species for their disruptive effects were variable, depending on year. Five non-host plant species were tested (beet, spinach, lettuce (two varieties), carrot and parsley); cabbage maggot oviposition was reduced by lettuce. The percentage of vertical profile of cauliflower covered by the non-host plant significantly influenced the numbers of eggs laid. -- Although undersowing cauliflower with winter wheat reduced cabbage maggot egg numbers in one of the two years, competition was intense and cauliflower yields were compromised. -- Relay cropping reduces the time that crops overlap in the field competing for resources. There were fewer D. radicum eggs collected from cauliflower relay cropped with lettuce than monoculture and competition was minimal. Delia platura ID. Florilega responded similarly to D. radicum in 2003, but in 2004 the opposite was true. This is the first study to demonstrate that relay cropping can reduce egg-laying by D. radicum while minimizing competition between component crops for key resources. -- Comparison of oviposition data from the 1950s to data from the diversification studies indicate that D. platura ID. florilega eggs were more prevalent than D. radicum in 2003-04 than fifty years earlier. In 2003-04 species proportions varied between year (2003 vs. 2004) and diversification study (undersowing vs. relay cropping).

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