Friday, 13 July 2018

Abundant parastioids in canola! (Jul 12, 2018; Wk 10)

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. This year, in some canola fields around Lethbridge AB, an abundant parasitoid wasp was noticed at the time when fields may be sprayed. The wasp was identified as Diolcogaster claritibia (Fig. 1; thanks to Vincent Hervet and Jose Fernandez for confirming identification).

The wasp is a parasitoid that attacks diamondback moth larvae and recently abundant in some fields in 2017. In some of the fields sampled, as many parasitoids as cabbage seedpod weevil (i.e., nearly one per sweep) were observed. In the fields sampled (i.e., around 10), cabbage seedpod weevils were below thresholds on average, though some spots may have been close to the threshold of 2-3 weevils per sweep.

The above observation emphasizes the value of beneficial arthropods like Diolcogaster claritibia.  It is important to recognize that foliar applications of insecticides kill beneficial insects like this small wasp (about 2 mm) which attacks and helps regulate pest populations of diamondback moth or other Lepidoptera, including cutworms and cabbage worms. Thus, think beneficials before you spray!

Figure 1.  Diolcagaster claritibia adult measuring ~2mm in length (Photo credit J. Fernandez, AAFC-Ottawa).

Learn more about beneficials by accessing Field Heroes and all the Blog's Parasitoid posts.