One of the best aphid predators for indoor and outdoor crops is the tiny parasitic wasp Aphidius colemani. These North American natives are produced in insectaries for the biocontrol industry, but they can be raised in any growing system with the right conditions. Growing banker plants to rear Aphidius colemani is like putting money in the bank. Instead of buying Aphidius on a regular basis, you can produce your own on barley or oat grasses that have been inoculated with cherry oat aphids. This establishes them in the greenhouse before aphids become a problem.

You may wonder, why would I ever bring aphids into my greenhouse? Cherry oat aphids (Rhopalosiphum padi) are pests of wheat, oats and barley (monocots) and will not survive on ornamental crops that aredicots. This allows them to exist in most greenhouses and provide habitat and food for the aphid parasite Aphidius colemani. As the Aphidius population grows, they spread throughout the greenhouse hunting down aphids, often finding them before you do. 

It's essential to produce fresh banker plants throughout the growing season, so a separate area is needed where the parasitic wasp is excluded while the grass and cherry oat aphids grow. This allows overlapping generations in the greenhouse. Start with 2 banker plants per greenhouse, adding fresh banker plants until July. The entire system takes 4-6 weeks to get started, so it’simportant to begin early in the season or as soon as crops are growing in the greenhouse. Banker plants can remain active for several months.

Why stop in July? There’s always a smaller bug and it’s called a hyperparasite. They show up in late summer and start laying their eggs inside of the aphids that have already been parasitized by Aphidius. You can tell if these hyperparasites are present by a jagged and uneven exit hole in the aphid mummy (Aphidus leaves a clean round exit hole). Hyperparasites can wipe out an Aphidius colemani population if allowed to reproduce. 

Try growing banker plants in 10 inch hanging baskets for easy placement around the greenhouse. Put them on a regular watering and fertilization schedule and try not to wet the foliage while watering. Adding dates to the pots can help for future reference. Once you get aphid banker plants in the bank, consider making future deposits for your growing system: pepper banker plants for Orius, Mullein banker plants for Dicyphus and Alyssum banker plants for numerous beneficial insects. Your savings will take you far.

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