Forest Preserve District of Cook County, Illinois
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Parasitic Wasps
Nature Bulletin No. 357-A    November 8, 1969
Forest Preserve District of Cook County
George W. Dunne, President
Roland F. Eisenbeis, Supt. of Conservation

Nearly everyone thinks of insects as enemies of mankind, and many of them are. Insect pests bite us. They also bite and aggravate our domestic animals. They spread diseases. They damage or destroy our crops and trees. They infect our food, our clothing and our dwellings. Men and insects have always been at war but, even with all our modern chemicals and other weapons, we have never been able to exterminate one single species of insect from the face of the earth. If it were not for the beneficial insects -- our friends -- the human race could not survive.

Certain insects produce valuable materials such as honey, beeswax, silk and shellac. Without insects there would be few crops, no gardens of vegetables or flowers, no fruits, no tobacco, no shrubs, nor most of the plant growth that enriches our landscape, because about 85 percent of all flowering plants require cross pollination of their blossoms by some sort of insect. Insects also enrich the soil. They serve as scavengers. And they supply more than half the food for birds, freshwater fishes, reptiles, amphibians and small mammals.

Equally important is the fact that insect friends of man do more than he could ever do himself in keeping the harmful kinds under control. Some are predators that catch and devour their prey -- like the ladybird beetles that saved the citrus orchards of California from destruction by scale insects. Some are parasites that invade the bodies of other insects, or their eggs, and kill them. Now, after centuries of disturbing the "balance" of nature in so many ways, we are beginning to look more and more for these natural enemies of insect pests. We use them. Most important are the parasitic wasps -- relatives of such "social" insects as bees, ants, and the stinging wasps.

Some lay their eggs in or on the larva of another insect and as many as 3000 may develop in one cabbage worm. Often, a big green tomato worm may be found dead or dying with a lot of small white slender objects attached to its body. These are cocoons made by larvae hatched from eggs laid by a parasitic wasp. Among the parasitic wasps are those that lay their eggs in the eggs of other insects, and some are so tiny that several may develop in an egg smaller than a pinhead. These destroy many of our most injurious pests such as chinch bugs, boll weevils, codling moths, and asparagus beetles. They have been propagated and released by millions in infested fields and orchards. Some parasitic wasps attack only one species, or a few closely related species, while others prey on a great variety of insects. Bless 'em.

There are four main families of parasitic wasps. Most conspicuous are the ichneumons -- commonly and mistakenly called Ichneumon Flies - - which include some of the longest insects found in the United States. The females of one, the Long-tailed Ichneumon, have an overall length of 5 or more inches. Her body is less than two inches long but she has long, constantly vigrating antennae and an ovipositor, or egg- placing organ, consisting of stout hairs three or four inches long. We saw hundreds of these females on a dead tree, not long ago. With that eggplacer, somehow, she finds an invisible crack or opening to the burrow of the woodboring "pigeon horntail fly". She lays an egg. The egg hatches. Her larva creeps along the burrow and latches onto the horntail larva. It feeds on its blood and soft tissues but avoids the vital organs until last. By and by, a mature ichneumon emerges. But no horntail.

One little ichneumon looked up and said, "What a long tail you have, grandmother!"

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