"Got aphids? Call in the reinforcements with banker plants"

Undeniably, a relatively new and promising strategy of biological pest control called “banker plants” has a name that lends itself to painfully obvious puns. Be that as it may, you can bank on it—or, if you prefer, take it to the bank—that banker plant systems have a key role to play in integrated pest management (IPM), especially when employed in greenhouses. Also known, more formidably, as “open-rearing systems,” banker plants are mobile habitats that supply growers with predators and parasites which are natural enemies of insects that attack cultivated plants.

by Edward Ricciuti

“As a biological control strategy, banker plants offer a novel non-chemical approach to managing commonly encountered pests in the greenhouse,” write the Oklahoma State University-based authors of a new paper published Monday in the open-access Journal of Integrated Pest Management. The paper reviews existing research and examines use of banker plants as a tool for integrated pest management (IPM) in closed growing environments such as greenhouses and hoop houses and on its effectiveness against aphids, in particular.

To manage aphid infestations in greenhouses, growers can introduce banker plants that draw different species of aphids that don’t feed on the main crop but that, crucially, serve as attractive hosts for parasitoid wasps, which will then also parasitize the pest aphids on the main crop. Banker plants can be grown in pots and transported easily to be placed adjacent to plots of crops in need of aphid management. (Photo credit: Tracey L. Payton Miller, Ph.D.)

It may sound contradictory, but one way to rid a greenhouse of aphids that suck the life out of daisies, pansies, and other ornamental flowers is to introduce more aphids: bird cherry-oat aphids (Rhopalosiphum padi), that is, whose menu is heavy on cereal grains but not ornamentals and vegetables grown in greenhouses. The paper describes how, raised in containers, or “banks,” of cereals such as oats and barley, bird cherry-oat aphids are used as an alternate host for the wasp Aphidius colemani. The tiny wasp lays its eggs in both the bird cherry-oat aphid and two other species, the green peach aphid (Myzus persicae) and melon aphid (Aphis gossypii), both of which can wreak havoc in greenhouses.

The female wasp is attracted by the smell of both aphid honeydew and odiferous distress signals—i.e., scent emissions—given off by plants under attack. She injects a single egg in a host aphid per sitting but may visit hundreds of aphids in a few days. As the wasp larvae develop into adults, the host aphids become moribund, virtually mummies. Even the presence of a wasp can alarm aphids so much that they drop off plants to the ground, where they usually die.

Read more at Entomology Today