News > Day Three > Know your friends in the field
Prairie farmers should pay more attention to the insects in their fields, according to a University of Alberta (U of A) researcher.

Using a sweep net can be an important investment of time and money in identifying both good and bad insects in a crop. -- Lee Hart photo

While some of those insects  are unwanted pests, there are also dozens of beneficial insects that often prey on those pests, says Lloyd Dosdall, a former provincial entomologist who’s now an associate professor at U of A.

In a presentation to the 2010 FarmTech conference in Edmonton this week, Dosdall says he isn’t opposed to using insecticides to protect crops when warranted. However, he explained, while the pests move in with potential to produce crop damage, in many cases predators to those pests aren’t far behind.

While a fair bit of attention has been paid to biological control agents (insects) that control weeds such as Canada thistle, purple loosestrife and leafy spurge, there are also a number of beneficial predator insects that are very effective in controlling common crop pests such as diamondback moths, root maggots, cabbage seedpod weevil, cereal leaf beetle and wheat midge.

“Often when we think about beneficial insects to cropsm we first think about honeybees, which help with the pollination process,” says Dosdall. “But even with pollintation, there are many other species that help in pollinating crops.”

Butterflies, thrips, wasps, hundreds of fly species and even beetles are other  insects that help pollinate crops as they move from plant to plant, and many are not harmful to the crop itself.

But Dosdall’s research over the years has shown there are many natural insect predators that help control common crop pests.

In controlling diamondback moths, for example, a small parasitic wasp called Diadegma, commonly found in Western Canada, is very effective. As the moth is carried into Canada’s canola-growing regions on wind currents from the U.S. and Mexico, the Diadegma are soon to follow.

In years when there are heavy infestations of diamondback moths, Dosdall says, he has seen fields where there are clouds of Diadegma living in the canola swaths feeding on the moth larvae.

Looking at field spraying statistics, he says, in 1995 and 2001 Alberta farmers spent $42 million and $86 million, respectively, in field spraying costs to control diamondback moths. In 2003 and 2005, spraying costs were estimated at $4 million and $3.5 million, respectively. Dosdall credits part of that significant reduction in spraying costs to the effectiveness of the parasitic wasp.

Root maggots have a very effective predator called Aleochara, a beetle that feeds on the root maggot eggs and larvae. A number of parasitic insects, such as Chlorocytus, are effective in controlling cabbage seedpod weevil. A small parasitic wasp has been found to be effective in controlling cereal leaf beetle, and another parasitoid, Macroglenes, is effective in controlling wheat midge.

Dosdall says it’s important for producers to know what insects -- harmful and beneficial alike -- are in a crop. And he says a few minutes spent with a sweep net can be of significant value.

He also recommends producers not only follow good production practices, which produce a healthy, vigorous crop that can better withstand crop pests, but also follow practices that benefit populations of beneficial insects.

Those practices include using good-quality seed and getting the crop off to a good start; using a sweep net to see what insects, good and bad, are in the field; managing time of spraying to control the pests but to reduce impact on beneficial insects; and following reduced-tillage or zero-till cropping systems, which also benefit the beneficial insects.

-- Lee Hart is a field editor for Grainews in Calgary.