Pteromalid Wasp

Description:

Pteromalus puparum is a tiny pteromalid wasp that develops inside pupae of the imported cabbageworm and other caterpillar pests. Adult wasps are 3-4 mm (1/8 inch) long and feed on flower nectar. Females are shiny black, while males are a metallic greenish bronze and are normally smaller than the females. The wasps fly short distances of less than an inch, which gives them the appearance of hopping. Females lay eggs in either the prepupae or newly formed pupae of the host, depositing up to 700 eggs during her lifespan. More than 200 offspring can be produced within each cabbageworm pupa. Parasitized pupae turn from green or gray to dull brown as the wasp larvae develop over about three weeks. Unparasitized pupae change from green or gray to yellowish white as the butterfly inside reaches maturity. One or more small round exit holes in the pupae indicate the wasp parasites have emerged. The wasps overwinter as mature larvae within the host pupae. The wasps will parasitize other caterpillar species when the imported cabbageworm is scarce. Because the wasps attack only the pupae, caterpillar feeding is not reduced and significant damage can occur, especially if cabbageworm population levels are high. The benefit of this parasite is in reducing the number of adults, and thereby reducing the size of the subsequent generation.

Notes:

spotted in my back yard