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Colorado potato beetle tolerance increasing

The Colorado potato beetle has been raising the ire of potato farmers throughout North America for many years. The stubborn bug is resistant to many insecticides, making control very difficult. Yet one insecticide class, neonicotinoids, has been highly successful at getting rid of the pest in many areas of the continent. Growing evidence of resistance to neonicotinoids, though, has scientists cautioning producers.

Dr. Galen Dively, of the Department of Entomology at the University of Maryland, says resistance to neonicotinoids is starting to show up in some areas of the US and eastern Canada. He predicts that widespread shifts in susceptibility are imminent. Common brand names of neonicotinoid class insecticides include Admire, Assail, Actara and Alias.In the late 1990s, Dively developed a baseline frame of reference for susceptibility to neonicotinoids by collecting Colorado potato beetle samples from North America and Europe. “You have to know how susceptible this beetle is,” he says, adding research gauged the rate of insecticide required to kill 50 percent of the test beetle population.

The best strategy for controlling Colorado potato beetle is rotation. Photo Courtesy Of Eugenia Banks, OMAFRA.

With that information, Dively is now able to judge an insecticide resistance trend before farmers see the evidence in the fields. He says Colorado potato beetle resistance to the neonicotinoids was found in parts of Maine in 2007, although not in the northern potato growing regions of the state. At the same time, some resistance has shown in Ontario and Quebec already. He predicts eastern Canada is on the brink of facing increased resistance to neonicotinoids and that resistance could spread during the 2008 season. “It’s going to take off quickly,” he says.

Rachel Cheverie is potato industry co-ordinator with the Prince Edward Island Department of Agriculture. She says evidence of neonicotinoid resistance has not shown up on the island, yet. “Judging how difficult it is to find beetles to collect, neonicotinoids are still having an affect,” she says. “We’ve really knocked the population back in the province.” But she cautions producers not to become overconfident with the effectiveness of this class of insecticides. “Just because we don’t have resistance here yet, there is resistance in other areas,” she says, noting nearby Maine and Quebec.

Dively explains that insecticide resistance in the Colorado potato beetle develops and grows in a similar way as antibiotic resistance in people. Just as some people do not respond to antibiotics, some individual beetles do not respond to some insecticides. As their populations grow, so does the resistance. “They would survive and they would pass that gene on to the next generation – it’s evolution,” he says.

Cheverie explains the reason neonicotinoids are so effective on the Colorado potato beetle is because of their systemic insecticide. Applied at the seed stage or in furrow at planting, the insecticide spreads through the plant as it grows. The beetles are destroyed once they ingest the neonicotinoid when they bite into the plant.

She says it is important for producers to use different modes of action when fighting the beetles to prevent resistance from building up. Instead of using neonicotinoid class insecticides at planting every year, use foliar products with different modes of action and have strong rotational plans in place in the field. Mixing up the controls against the Colorado potato beetle will help ward off resistance, Cheverie says. “Resistance is inevitable. If you keep using the same product over and over, you’re going to get resistance,” she states.

Dively agrees. He says it is vital for producers to use a variety of control methods since each incorporates a different mode of action against the Colorado potato beetle. “Switching to something outside the class means a different mode of action is in effect to kill the beetle, attacking different parts of its nervous system,” Dively explains.

“Try not to use the same insecticide year after year, or even within the season. Go with a neonicotinoid and then come in with something else, so the beetles that are resistant to one mode of action will likely be killed by another,” he says.

Most important for effective control, Dively and Cheverie agree, is crop rotation. Dively says even if producers only move potato crops a short distance from the previous year’s crop, it makes a difference. The Colorado potato beetle overwinters in the soil and “doesn’t go far” in the spring, he explains. Next, scout fields for signs of the Colorado potato beetles in the spring, he says, and hold off on using insecticides unless necessary.

By using a variety of defenses against the Colorado potato beetle, potato farmers have a fighting chance to win the fight against the devastating pest and help the industry as a whole in helping slow resistance to some of the most efficient insecticides. -end-