Aphids are perennial problems in greenhouses everywhere, but biological control is an increasingly popular tool for greenhouse growers to manage these pests.
Here are some of the most commonly used beneficials for aphids, as well as handling, application and management suggestions to help you maximize the effectiveness of each.
■ Aphidius colemani and Aphidius ervi
Pests attacked: Aphidius colemani attacks small aphids such as green peach aphid or melon aphid. This species does not attack larger aphids such as foxglove aphid or potato aphid. Aphidius ervi attacks large aphids such as foxglove aphid or potato aphid. This species is not as effective against the smaller aphid pests as is A. colemani.
Identification: A. colemani is a very small, non-stinging wasp about the size of a fungus gnat with thin, black, thread-waisted body and clear wings. Aphidius ervi looks similar to A. colemani except the wasp is slightly larger.
Biology: The female wasp of both species lays an egg inside an aphid. The egg hatches into a maggot that develops inside the aphid, turning the aphid into a rounded, straw-colored “mummy” before the maggot finishes developing into an adult wasp and chews its way out of the dead aphid. Temperatures above 86°F reduce effectiveness.
How to check for shipment viability: Wasps are shipped as mummies mixed in sawdust or other carrier in bottles. Open the lid and some adults should be obviously active, or will be within a day or so.
How to release into crop: Sprinkle a small amount of mummy/carrier mixture into little containers shaded in the plant canopy and distributed throughout the crop or into aphid hotspots. Avoid drowning the mummies in the containers during overhead watering. Banker plants (barley or rye plants infested with bird cherry-oat aphid) offer a cheaper and more reliable way to maintain an effective level of wasps without repeated releases.
■ Aphidoletes aphidomyza
Pests attacked: A wide range of large and small aphid pests.
Identification: As an adult, A. aphidomyza is a small, midge-like fly roughly the size of a fungus gnat. Eggs are orangish and long with rounded ends, often laid in batches of several eggs. Larvae are bright orange maggots usually found within aphid colonies.
Biology: Adult females do not eat aphids but lay their eggs within patches of aphids. Eggs hatch into orange maggots that eat aphids. The adults are active at sunrise and sunset.
How to check for shipment viability: Aphidoletes are shipped as pupae (cocoons) in vermiculite in container trays or bottles and emerge as adults soon after arrival. A small amount of the mixture can be set aside in a see-through container in the shade and checked in a day or so for adult emergence.
How to release into crop: Place opened trays or bottles in shaded areas beneath aphid infestations. Do not scatter the mixture. Keep the mixture dry. Release rates are available from the suppliers.
■ Chrysoperla carnea (Green Lacewing)
Pests Attacked: Green Lacewing attacks a wide variety of insects and mites, although it is usually used against aphids. Larvae are cannibalistic.
Identification: Adults are lime green with golden eyes and large, net-like wings. Larvae are long, thin and variable brownish-greyish in color, with large, sickle-shaped mandibles.
Biology: The female lays eggs on long stalks. Larvae hatch and crawl down the stalk to search for prey. They pupate in fuzzy whitish balls. Lacewings usually do not cycle in a greenhouse setting. Larvae are predaceous but adults are not.
How to check for shipment viability: If releasing eggs, hold some back from a shipment to watch for hatch. For shipments of larvae, sprinkle a small amount of carrier onto paper and look for moving larvae.
How to release into crop: Release into aphid hotspots. If releasing larvae shipped in corrugated cardboard cells, pull back some of the fine gauze that covers the cells and tap out the desired number of larvae onto foliage. For larvae shipped in buckwheat hulls, sprinkle onto foliage. If releasing eggs, wet foliage to aid in eggs adhering to leaves, then broadcast eggs.