Aphidius Wasp

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Amazing Animal

June 21, 1999|By Patricia Chargot

WHAT is it? It's a group of small, but very important wasps. They're only one-eighth to one-sixteenth of an inch long. They have tiny wings and can fly. They're the No. 1 enemy worldwide of aphids, soft-bodied sucking insects that destroy garden plants, trees and shrubs. They're an aphid parasite.

WHAT does that mean? Parasites are animals that live in, with or on other animals. They depend on those animals for their very existence.

How does the WASP get in the aphid? It stands close to the aphid, thrusts its abdomen forward and stings the aphid in its abdomen.

What can the aphid DO? Not much, but it can warn other aphids to get away. It produces a warning chemical and releases it through tiny structures on its abdomen that look like exhaust pipes. When other aphids smell it, they walk away or drop off the plant. They can't fly.

What happens to the ONE that gets stung? It gets injected with a wasp egg, which grows inside it. The wasp larva feeds on the aphid's insides. But the aphid doesn't die for a long time -- not until the wasp larva is almost completely grown. The aphid swells as the larva grows, stiffening into a leathery, brown wrapping. Scientists refer to these as mummies.

THEN what? The adult wasp eats its way out through a small round hole. Meanwhile, about 50 other newly hatched wasps -- all with the same mother -- are emerging from other aphid mummies. Within a few days, the females will mate, then the females will start stinging aphids. The wasps live for only two to three weeks.

How MANY parasitic wasps are there? There are 1,700 North American species alone. Of those, 20 specialize in attacking aphids. (The others attack other kinds of insects.) They will all soon emerge from their winter hibernation.

Source: David Smitley, professor of entomology, Michigan State University.

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