SPRAY SENSE Entomologist Jim Bratch says spraying as “a precautionary principle” may be a bad move
It’s easy to forget about the beneficial insects in your crops when you are focused on eradicating pests of all kinds.
“When you calculate the economic loss from your pest insect, add about 20 per cent to it, and think about the beneficials that are in there,” said Jim Bratch, an entomologist with Alberta Agriculture in Lacombe.
“Nobody will expect you to take an economic hit to protect those beneficials, but be aware that they are there. If you do get the urge to spray as a precautionary principle, maybe hold off.”
There hasn’t been a lot of research of beneficial insects, and Bratch is trying to learn more about the actual payback they provide. Some of the good bugs have very specialist roles, while generalists — largely two types of beetles (carabids and rove) — have multiple benefits.
Growers may also be surprised with the number of beneficials that may exist in their crops, he said.
“When we did research about five years ago, we found about 50 different species of carabids and 10 different rove beetles in canola alone at this research station,” Bratch said.
Only five or six of the species of carabids were in high numbers. The types of beetles found in a production system will differ depending on the region of the province.
There are only a few people in Canada who specialize in identifying these types of beneficials, so samples are often sent all over the country. Researchers need to find different ways to trap insects in order to monitor and evaluate their presence in a production system. At the Lacombe research station, researchers are using pitfall traps, which capture rove beetle and carabid activity and density. Researchers are also using nets to sweep canopies and monitor activity. Many of the traps are catching Terasticus, a black beetle which will eat everything. These ones are generally in high numbers in most systems, but are often found in canola.
Root maggots found in canola are a food source for all the generalists, said Bratch. The canola generalists also feed on cutworms when there’s an outbreak. One type of insect that lives in canola is entirely dependent on root maggots for its dietary needs.
“These really keep the root maggots from lowering yields,” he said.
Some beetles will also eat weed seeds during certain stages of their life cycle, reducing the weed population in crops.