FARMINGTON — Nestled among petunias, geraniums and pepper plants are containers of young oat plants that are battle sites for predatory slaughter.

The duel is between the beneficial parasitic wasp and its favorite food — aphids — the bane of greenhouse growers.

Robin Jordan, the owner of Robin’s Flower Pot, prefers to use bio-controls rather than chemical pesticides to battle insect infestations. She is using a system known as “banker plants,” with which she is raising aphids on oat plants that will become a food source for the voracious, bug-eating wasp.

“We have been using beneficials for about six years and we have been able to keep our greenhouses pretty clean,” she said. “This is the first time we have used the banker-plant system.” Jordan owns the nursery and garden center at 387 Webster Road in Farmington with her husband, James.

“Aphids multiply so rapidly and before you know it, you have a problem,” she said. “This way, we are building up our own population of beneficial insects before an infestation breaks out. It means we won’t have to buy them on a regular basis.”

Dr. James Dill, the University of Maine’s pest management specialist, said the idea is to grow banker plants of oats or barley and use them to rear certain varieties of aphids that only thrive on that particular species.

Once the aphid colony is established on the banker plants that are being grown in an encased, screened-in container in the greenhouse, the grower releases the parasitic wasps.

“The wasps lay eggs in the aphids and they hatch and eat the aphids from the inside out,” Dill said. “You end up with a ‘mummy’ and a little hole where the new wasp will emerge and move on to another aphid.”

The wasp-infested plants, dotted with barely-visible mummies, can then be strategically placed in greenhouses where they hatch, fly off and attack aphids on other plants, he said.

The system is part of a program known as integrated pest management. According to the University of Maine Cooperative Extension Web site, it is a “sustainable approach to managing pests by combining biological, cultural, physical and chemical tools in a way that minimizes economic, health and environmental risks.”

“Growers can then sell pesticide-free plants and tell their customers that they are raising their crops under an (integrated pest management) program,” Dill said.

“Aphids are born pregnant and can give live birth, so they can keep pumping out new aphids constantly,” he said. “You can have a huge population of aphids in a greenhouse pretty quickly.”

The advantage of the banker-plant system is that growers can raise a continuous supply of wasps to use when needed, Dill said. His office has promoted the technique for several years, but only a handful of commercial growers in Maine are using it, he said.

At Provencher’s Landscaping Nursery on River Road in Lewiston, owner Roger Roberge is a member of the state’s Integrated Pest Management Board and a longtime proponent of the method. He has used beneficial insects in his three greenhouses but has not tried using banker plants.

“The important thing in all of this is that you have to be very knowledgeable about what you are trying to treat, understand an insect’s life cycle and become familiar with using the least hazardous, organic-based products,” Roberge said.

He said he and his staff regularly scout by eye and with a hand lens.

“You need to be scouting constantly so you can catch things before they become a problem,” he said.

Jordan said she also brings in beneficial insects that feed on thrips, white flies and mites. But she believes in letting nature take its course whenever possible.

“Last year, we had some heliopsis plants that became loaded with aphids,” she said. “Then some beneficial lacewings flew in and took care of them.”

At Hummingbird Farm on Bean Street in Turner, owners Cindy and Brian Tibbetts grow 100 varieties of clematis, specialty geraniums, tree peonies and herbs in their greenhouses. They also do not use chemical pesticides and are believers in beneficial insects.

“We have used parasitic wasps and ladybugs, and we found they will hang in there even after the problem is gone,” Brian Tibbetts said. “They have come back and appear to be self-perpetuating.”

For home gardeners, Jordan advises people not to tear out plants or spray with chemical or organic products at the first sight of a few bugs.

“If you see an aphid or a bad bug, relax,” she said. “When you spray, you are not only spraying the pest but also are killing the good bugs.”

Handpicking bugs like potato beetles or Japanese beetles and plopping them in a jar of vinegar and water or a dish soap solution should be tried first, Jordan said.

And before tearing out “weeds” such as milkweed — a plant loved by hummingbirds and butterflies — if pods are found covered with insects, take the time to identify what they are, she said.

“There is a good chance they will be beneficials,” she said.

For information on identifying pests and predators and to learn more about integrated pest management, go to the University of Maine Cooperative Extension’s Web site at and click on “pests and plant disease management.”

Or, search for “Maine insects” on Goggle and click on the first entry for the Cooperative Extension’s insect fact sheets.

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