Archives

Parasitic wasps help B.C. apple growers limit pesticide use

Parasitic wasps are helping B.C. apple growers fight pests and establish a reputation for low-pesticide production, say scientists at Agriculture and Agri-Food Canada’s Pacific Agri-Food Research Centre.

The wasps are a natural enemy of Phyllonorycter mespilella, a moth pest known as a “leafminer” because it feeds inside the leaves of fruit trees. In cooperation with researchers, extension specialists and packing house workers, growers across the Okanagan and Similkameen Valleys have learned to monitor the wasp’s control levels before deciding if other controls are necessary. So far, they’ve found the wasps are more than up to the job, limiting the need for pesticides to rare high-risk situations.

“These wasps are so small the average person may never see them,” says researcher Dr. Joan Cossentine. “But they have kept the leafminer population under control – the wasps are so effective that usually other controls are not needed.”

Small infestations of leafminers are harmless. But high populations can cause premature ripening, leaf and fruit drop, and reductions in apple quality. B.C. growers regularly monitor the wasp activity, using a threshold of a minimum 30 percent parasitism, as recommended by researchers, to determine whether wasps have the leafminer population under control.

“The growers have learned to tear open the leaves, to check for the wasp activity,” says Cossentine. “Two of the main parasitic wasp species feed on the outside of the leafminer – so you can see them in action. The growers know if the level of parasitism is about 30 percent, they don’t have to bother considering other treatments.”

Today’s success is the result of a pest control strategy that began more than a decade ago, when leafminers first moved north into B.C. from orchards in Washington State.

The leafminers were resistant to pesticides commonly used in the U.S. orchards. When American producers tried to control the leafminer by applying a more toxic pesticide, this practice killed a range of beneficial insects, including the parasitic wasps.

To avoid the same mistakes, B.C. researchers responded with an approach called integrated pest management (IPM). It gives growers more options for safe, cost-effective and sustainable pest control, based on a more sophisticated understanding of the pest and its role in the local ecology.

When the resistant leafminer populations began to move across the border, Cossentine and other B.C. researchers urged caution. With help and advice from their American colleagues, they had learned about the value of parasitic wasps as natural enemies of the leafminer.

“We monitored an orchard close to the border and it looked very promising,” remembers Cossentine. “The parasitic wasps had apparently followed the leafminers across the border and were killing almost 90 percent of the leafminer larvae.”

Based on similar results at several orchards, the scientists, along with provincial extension and packing house workers, launched an education campaign to convince growers not to spray, she says. The promising results held, and after three years of careful monitoring, researchers concluded they could rely on the wasps to provide sustainable control. To this day, B.C. apple growers rely almost exclusively on natural wasp parasitism to control the leafminer.

“If our growers had stepped in with a very toxic chemical, they would have created a lot of damage by killing beneficials,” says Cossentine. “Instead, the leafminer has been controlled biologically without much commotion at all. I think this is an ideal example of integrated pest management which was handled correctly from the very beginning.”

IPM is part of Agriculture and Agri-Food Canada’s mandate to promote innovation for growth, maintain security of the food system and protect the health of the environment.

© 2002 Meristem Land and Science
Meristem® is a registered trademark of Meristem Information Resources Ltd. All rights reserved.
Legal Disclaimer