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Survey of Delia species of maggots affecting onion in Quebec, Ontario and Eastern Provinces

Project Code: PRR17-010

Project Lead

Julia Mlynarek - Agriculture and Agri-Food Canada


Evaluate damage to onion crops caused by Delia root maggot species and determine which species are the major contributors of damage

Onion crops grown in Canada are susceptible to root maggot pests (Delia platura, Delia florilega, and Delia antiqua). Although Delia antiqua, the onion maggot, is often considered the primary pest, recent studies have demonstrated that the seed corn maggot (Delia platura) and the bean seed maggot (Delia florilega) may be causing a larger proportion of root maggot damage than previously thought. These pests cause damage by feeding on the seedlings and bulbs. Current management strategies for Delia species include pesticide treatments, however it has been shown that Delia antiqua has developed resistance to chlorpyrifos, the pesticide of choice for root maggot control, and pesticides may be detrimental to bio-control agents that could be used to control these pests. Research is on-going in the development of biocontrol approaches to manage root maggot pests, but this research is still in its infancy. Knowledge on which Delia species cause the most damage to onion crops is also limited due to challenges associated with Delia species identification, especially identification of Delia florilega. This work was identified as a priority for action under Pesticide Risk Reduction’s Strategy for Root Insect Pests of Carrot, Parsnip and Onion.

This one year project proposes to evaluate the Delia species, their presence in onion fields across geographical regions of Southern Ontario, Southern Quebec and Nova Scotia and the effect of each species on onion development. Studies will be conducted in commercial bulb onion fields in 3 to 4 sites within each geographical region to determine the ratio of each species within the overall root maggot complex, and in controlled onion field trials at two Agriculture and Agri-Food Canada Research Centres (Nova Scotia and Ontario-Harrow) to provide knowledge on the plant growth stage targeted by each species. Information on the damage caused to onions by individual Delia species will be obtained from growth chamber experiments.

Results obtained from this research will provide researchers and crop specialists with accurate information concerning species identity of root maggots and their potential for inflicting damage in onion growing regions of Eastern Canada. A better understanding of which root maggot species are affecting onion crops will lead to the development of management strategies to effectively address each species, which would benefit the industry by targeting controls at the species level, and by reducing ineffective pesticides use.

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