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Potatoes love tomatoes

If potato beetles could talk, they would be raving this season about a new local variety of tomato plant. Yes, tomatoes – and these same plants that are so very attractive to potato beetles may be able to usher in a new era of beetle control in Ontario and beyond.

Preliminary testing of the tomato variety Bugbait occurred this past summer at the University of Guelph’s Ridgetown College campus. It’s hoped the variety can work as a trap crop to control Colorado potato beetle infestations on potato crops. Contributed photo

Colorado potato beetles love potatoes but can also be attracted to other crops, such as tomatoes and eggplant.

If potato beetles could talk, they would be raving this season about a new local variety of tomato plant. Yes, tomatoes – and these same plants that are so very attractive to potato beetles may be able to usher in a new era of beetle control in Ontario and beyond.

The new variety – coined Bugbait by its discoverer Dr. Jim Dick – has undergone very positive preliminary testing at the Ridgetown College campus of University of Guelph this season, and expanded testing will continue next year.

The discovery of the variety was a lucky accident. “I was looking for green-stemmed mutants,” says Dr. Dick, CEO of tomato breeding company Tomato Solutions in Chatham, Ont. “I was able to find three in different varieties. It turned out I couldn’t use them as intended, but noticed that one of them, the Colorado potato, beetle ate it up – just destroyed it.”

It is this attractiveness that is the key to this variety’s potential to control potato beetles. Because they are more attractive than potato plants to the beetles, they may be used to serve as a “trap-crop” around the edge of potato fields. As long as there is sufficient foliage to keep the beetles happy, they will stay put.

Steve Loewen, a tomato breeder who works at Ridgetown, brought the mutant plants to the attention of Dr. Christian Krupke, a pathologist specializing in vegetable pest management. Dr. Krupke joined the faculty at Ridgetown in March 2008 after working at Purdue University in Indiana for three years. He is originally from Mississauga and has studied at the universities of Guelph, Simon Fraser and Washington state.

Dr. Krupke planted several dozen plants mixed with potato and other tomato varieties this season. “I have never seen this kind of attraction on a non-host plant,” he says. “From that point of view, I am very excited about it and doing work on it next year. I would characterize its potential [as a trap-crop] as excellent.”

In terms of why potato beetles like the foliage of Bugbait plants so much, Dr. Krupke says “My main theory is that there’s an anti-feeding compound missing in these plants. They most likely don’t have a secondary plant compound that would ordinarily control the beetle.” He adds, “In nature, this plant wouldn’t survive. It would be eaten down and killed and wouldn’t survive to the next generation.”

Dr. Krupke’s other theory is that Bugbait plants have something extra that’s attractive to the beetles, but he says “It’s far more likely that there’s something missing.” As to whether the beetles may be able to smell that the anti-feeding compound is missing or take an experimental bite and find it to be absent, Dr. Krupke says he would guess it’s the latter.

This winter, Dr. Krupke will probably seek a chemist colleague to help investigate the chemical differences between the foliage of Bugbait and other varieties. “It’s easier than you think [to identify plant compounds],” he says, a process which involves the burning of plant tissue samples in a gas chromatography machine.

Trap-plant control
What’s so exciting about Bugbait tomatoes is the fact that their attractiveness to potato beetles is only one of the qualities they possess that are critical to trap-plant success. Bugbait plants also grow a great deal of foliage, keeping the beetles fed for a substantial amount of time. “You need a trap-plant to grow well in southern Ontario weather and this tomato plant does that,” says Dr. Krupke.

In comparison, he points out that eggplant, which has also been studied as a potato beetle trap-plant, “doesn’t put on a lot of foliage in the best of times,” and really doesn’t do well in the cool, wet weather common in southern Ontario. “You need a crop that’s going to perform for you and you don’t have to baby,“ he says. “That’s the advantage of this tomato. It’s from commercial cultivars and it’s resilient.”

The lack of all these qualities together in one plant is the very reason why trap-cropping hasn’t been widely adopted as a method of potato beetle control. Potato beetles do, however, lend themselves to being controlled this way, says Dr. Krupke, because they walk into potato fields from the edge. “If you can trap them as they walk in and keep them there, then you have them and you don’t have to spray as much,” he notes.

Pest control challenges
Spraying is still an important management tool, even when trap-cropping is used. When the beetles on Bugbait plants should be sprayed is part of what Dr. Krupke will be investigating in 2009.

Trap-cropping, however, may be able to help with the problem of insecticide resistance. “This beetle has been resistant to everything we’ve tried in the last 40 to 50 years,” Dr. Krupke says. “Cross-resistance [to several pesticides] also happens.

“The way you prevent resistance is by not spraying the entire field all the time. You lower the pressure on the organism and kill only what you need to kill. What [trap-cropping] would accomplish is that you would spray the border of the field. Some will get through, but is it really worth spraying the entire field to kill them all? No.”

Resistance aside, potato beetles are also among the toughest pests to fight because of their high reproductive rate, says Dr. Krupke, and the corresponding high level of genetic diversity present in all those offspring. And, there are lots of potato beetles out there because the crop has been grown widely for a long period of time.   

Preparing for next summer’s testing of Bugbait will involve harvesting seeds this fall and getting in touch with willing potato growers. “The target is a commercial potato field ringed on all sides with this tomato,” Dr. Krupke says.