Does anyone know anything good about aphids? I’m really beginning to develop a rather intense dislike of these little pests—or to be more gentle, a dislike of the damage they inflict on plants. Although an aphid infestation doesn’t usually kill a plant, it does make the poor plant look as if it wishes it were dead.
A severe infestation can result in decreased and deformed fruit, flower and leaf production. Aphids are notoriously difficult to control. But we gardeners do have some tools we can use to manage these abundant nuisances. Among our tools is one that Mother Nature has thoughtfully provided: the braconid wasp.
When I think of a braconid wasp, I think of a minuscule, wasp-shaped super-hero, especially since members of this family can assist in the control of many types of insect pest populations. One group that is particularly useful for aphid management belongs to the genus Aphidius. Species in this genus are less than 1/8 inch (about 2 mm) in length.
Species within Aphidius tend to be black or brown, with a wasp’s typical narrow waist and transparent wings with some dark venation. Aphidius spp. are aphid elimination specialists. The adult female starts the process by laying a single egg in an aphid nymph. The nymph continues its nymph business until the egg hatches. Then, the wasp larva goes to work. It is an endoparasite which means it kills its prey by consuming it from the inside.
When the aphid nymph finally dies, it forms a “mummy.” Swollen, brown and hard, the mummy looks somewhat like the little piece of charred puffed rice that you didn’t want to eat. The wasp larva then attaches its mummified host to a leaf with a thread of silk, spins a cocoon, and pupates inside its dead host.
After the adult stage of the wasp emerges from its cocoon, it chews a hole through the body of its now mummified host and then flies away to start the aphid destruction cycle again. You may need a magnifying glass to see these mummies, but if you do, leave them there. It’s a sign that one ally in the war against aphids is on the job.
If you closely examine the mummies with a magnifying glass, you may see a single hole on the body of some mummies. This is the exit hole made by the braconid wasp to emerge from its host!
These braconid wasps are so in tune with aphid elimination that even their movements may help destroy them! While the adult wasps walk around looking for mates and aphids, they knock some of the aphids off the plant, thereby causing them to starve to death.
For many reasons, controlling aphids can be a formidable battle. First of all, they can reproduce faster than just about any other insect. They even use sexual AND asexual reproduction. This rapid reproduction results in shortening of time between generations and overlapping generations.
Rapid reproduction rates also increase the probability of aphids developing resistance to insecticides. Add the aphids’ increased resistance to insecticides to the fact that chemicals can also destroy their natural enemies, such as Aphidius wasps, and the end result can be a population explosion of the tiny plant suckers.
Who wants more aphids? Learning to recognize and encourage natural control agents like braconid wasps can be a very important step in responsible and successful gardening.
Beneficials in the Garden & Landscape is an Earth-KindTM program coordinated through Extension Horticulture at Texas A&M University. Earth-Kind uses research-proven techniques to provide maximum gardening and landscape enjoyment while preserving and protecting our environment.
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