The Backyard Jungle

Image Gallery Rose aphids

Here's the twelfth in a series of articles that will help you tell friend from foe in your garden.

Part XII: Aphid Control

by Ron West

In our last issue, we took a close look at the biology of the aphid. Now let's turn our attention to the types of aphids and what can be done to control them.

There would appear to be few plants that are not attacked by one species or another of aphids. The cabbage aphid ( Brevicoryne brassicae ) is gray with a white waxy coating and is found on most of the cole crops. The pea aphid ( Acyrthosiphon pisum ) is green and attacks many legumes.

Cotton aphids ( Aphis gossypii ) are found on cotton as well as on melons, beans, and beets; of variable color, they may be green, brown, or black. The floriculturists among us might eventually meet up with the rose aphid ( Macrosiphum rosae ), a green species that forms dense colonies on the buds and tender leaves of rosebushes. The list of destructive species goes on and on: bean aphid, peach aphid, apple aphid, potato aphid, woolly apple aphid, etc. Fortunately, the control of these pests differs little from one species to another.

Nature has numerous weapons with which she offsets the enormous reproductive capacity of aphids. There are, for example, many predators that feed on these prolific pests. The benefits of having ladybugs and green lacewings in your garden have been discussed in previous issues. Another important predator is the larvae of the hover fly (family Syrphidae). These can be recognized by their similarity to other maggots: They're legless, elongate and tapering, widest at the rear. Adult hover flies often bear a remarkable resemblance to yellow and black wasps.

Internal parasites also take their toll on the aphid population. The larvae of tiny braconid and chalcid wasps feed and develop within the bodies of aphids, eventually killing them. The unfortunate host takes on a ghostly appearance and becomes brittle. Such "aphid mummies" are easy to spot among their nonparasitized kin. The larva of the wasp may pupate within or outside its host, and it often leaves a small "door" at the point where it emerges from the aphid's body.