The Garden's Beneficial Insects: Chalcid Wasp

Get to know the beneficial insect chalcid wasp that preys on the eggs of garden predators.

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    About 12 mm in length, this leucospidid wasp is a parasite on the raspberry horntail, as well as being one of the largest chalcids and a superb mimic of the yellow jacket.

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

PART XVII: Chalcids

In my last column (in MOTHER EARTH NEWS N0. 97), I mentioned that one natural, effective means of controlling cutworms and other caterpillars in your garden is to introduce a tiny parasitic wasp species — known scientifically as Trichogramma — whose larvae feed upon the eggs of harmful insects. This time around, I'd like to expand on the use of Trichogramma and other chalcids as a natural means of controlling insect pests in your garden.

The 2,200 or so North American species of chalcids are members of a large superfamily (Chalcidoidea) which is divided into 22 families. Chalcids are typically wasplike in appearance and have elbowed (jointed and bent) antennae resembling those of ants. They differ dramatically from other wasps in size, averaging only two to three millimeters in length (though some reach 12 mm or more), as well as in the fact that their wings are practically veinless. Many chalcids have dark bodies and yellow legs, but some are brightly colored with a gorgeous metallic sheen.

Despite the chalcids' diminutive size, these garden helpers are death on the eggs and larvae of some of the most destructive varieties of insect pests, including two-winged flies, beetles, moths and butterflies, aphids, leafhoppers, scale insects, and whiteflies.

In addition to their devouring other insects in the embryonic or larval forms, certain chalcid species display a number of unusual, and therefore interesting, habits. For example, some chalcids are well known for polyembryony , in which anywhere from ten to over a thousand larvae develop from each egg . . . good news for the gardener who's plagued with insect pests and wants to introduce a large number of beneficial parasites quickly and with little effort.

On the other hand, another chalcid phenomenon — known as hyperparasitism — can work against the gardener, and occurs when a chalcid uses another parasitic insect for its host, thus negating the beneficial effect of the victim parasite. (In one species of chalcid, this hyperparasitism takes on a bizarre twist in that while the females are parasites of scale insects, the males are hyperparasites that attack the parasites of scale insects . . . including the females of their own species!)

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