If you see black beetles in your canola crop, thank them for doing a job for you. In a 1-year study of diamondback moth arthropod predators in southern Alberta, the black beetle (Pterostichus melanarius) had a predation rate of 9.5 larvae killed per day on average.
The study also found that rain washing diamondback moth larvae to the ground helped increase predation by this species and could prevent the need to spray insecticides.
However, according to Dr. Hector Carcamo, the Diadegma wasp is the key natural enemy here. “This parasitoid can reach very high levels of parasitism in the Prairies, so that the summer generation of the moth is too small to become a pest problem,” says Carcamo
Diamondback moth (Plutella xylostella) is a serious worldwide pest of Brassica cropping systems such as canola. Generally farmers manage it with insecticides. But it adapts quickly to chemicals so integrated pest management practices help curb moth populations with the use of natural enemies.