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Think beneficials before you spray!

Diolcogaster claritibia Photo: Carcamo
This small wasp does a big job controlling some crop pests in southern Alberta.

Dr. Hector Carcamo says be careful before you spray for cabbage seedpod weevil! “This year, in some canola fields around Lethbridge, we noticed an abundant parasitoid wasp at the time when fields may be sprayed,” Carcamo says. 
Jose Fernandez and Vince Hervet helped identify the wasp as Diolcogaster claritibia. It is a parasitoid of diamond back moth larvae. This pest was abundant in some fields last year.

“In some of the fields we sampled there were almost as many parasitoids as cabbage seedpod weevils, near one per sweep” he says. In the fields sampled (around 10), the weevils were below thresholds on average, though some spots may have been close to the threshold of 2-3 weevils per sweep. Carcamo insists that, “It is important to think about the impact of spraying on the populations of beneficial insects like this small wasp (about 2 mm) because they can help keep other pests like diamond back moth or other Lepidoptera such as cutworms and cabbage worms from reaching pest status. Thus, think beneficials before you spray!” 

The cabbage seedpod weevil is a chronic pest of canola in southern Alberta and south western Saskatchewan; it has recently reached Manitoba as well. The pest is managed with insecticides, which are sprayed at early flower.