The Organic Report: Beetle Banks

About five years ago, Brad Bailie, owner of Lenwood Farms in Connell, WA, was introduced to the concept of “beetle banks.” These “banks” are non-disturbed areas on the farm where there is minimal use of chemical pest controls and they are designed to encourage the development of predacious ground beetles.

As an organic grower, Bailie, who operates a 600-acre farm producing potatoes, onions, peas, and grains, was interested in finding a way to keep the beneficial insects, such as the ground beetles, around to prey on the insects that can harm his crops. “The beetles also have been known to eat weed seeds,” he adds.

Where It Started
According to Gwendolyn Ellen, who is part of the Farmscaping for Beneficials Project at the Integrated Plant Protection Center at Oregon State University, the idea of the beetle bank comes from the United Kingdon (UK) and New Zealand. Growers in the UK and New Zealand are paid on a kilometer-by-kilometer basis to create beetle banks to promote predatory insects, she says.

“In the UK, researchers have found that beetle banks supply refuge and conservation of species at several trophic levels,” says Ellen. “We also see other beneficials there such as native pollinators, lady beetles, and spiders. The predacious ground beetles and spiders target crop pests that occur mostly on the surface and in the soil such as cucumber beetle larvae, Colorado potato beetle larvae, snails and slug eggs, etc.”

Growers who want to encourage the beneficials to stay on their farm create diverse habitats, says Ellen. “They not only have to provide refuge, they have to provide food such as pollen, nectar, and alternative prey for the beneficial insects. The beetle bank is the area where they can overwinter near crops and from where they will forage in the spring and summer.”

The areas Bailie offers the beetles on his farm are in the corners of fields that he typically finds more difficult to farm. He has designated these areas as permanent insectaries. It is in these field corners that he plants different types of flowers along the edges of the roadways. Bailie makes sure no tilling takes place in those areas in order to help build up the habitat.

The insectary plantings include native flowering plants in hedgerows and small patches of native and horticultural flowering plants that reseed for high energy food sources, explains Ellen. “Included in the habitats are beetle banks, which are raised areas of native and non-native grasses that form bunches of organic matter at the base and provide perfect winter habitat for predacious ground beetles and spiders,” she adds.

Building Banks
Building a habitat for beetle banks or building beetle populations doesn’t happen overnight. According to Ellen, it takes three to five years to build up beetle populations. She adds that it takes just one season to build up populations for the pollen and nectar feeders (parasitic wasps and native pollinators) and other predators such as true bugs, which include assassin bugs, minute pirate bugs, and damsel bugs.

“Determining when you have enough [beetles] to impact pest populations is very difficult as it is not a linear approach,” explains Ellen. “Sometimes no economic damage from pest outbreaks is all the assurance you may get from the generalist predators. This will vary from year to year as pest pressure and weather events vary, as well.”