Ohio State University Extension Fact Sheet

Entomology

1991 Kenny Road, Columbus, Ohio 43210-1090

Nuisance Parasitic Wasps

HYG-2113-95

Occasionally certain parasitic wasps may become a nuisance when found in homes or simply cause concern when single individuals are found. Homeowners may confuse these insects with winged ants, stinging wasps, or other household/structural pests, causing much alarm. Actually nuisance parasitic wasps are very beneficial to humans since they parasitize many different kinds of harmful insect pests. They live outdoors and are usually accidental indoor invaders, often attracted to lights. They cause no harm to humans, pets, structures, possessions or crops. However, some Ichneumon wasps can sting severely when mishandled.

Ichneumon Wasps

Adults vary in size from 1/8 to 1-1/2 inches with long, many-segmented antennae and long, slender bodies. Females have long ovipositors (egg laying tubes), the longest of which is six times the body length. Legs are long and slender.

The long-tailed Megarhyssa is the largest ichneumon wasp in Ohio and recognized by three, long, hairlike parts of the ovipositor (up to five inches long) on females. This wasp is about one inch or more, reddish-brown, slightly marked with black and red with brown spots in the wings. Megarhyssa atrata (Fab.) measures 1-1/2 inches with the body and wings black while the head and most of the legs are yellow. These insects parasitize the larvae of pigeon tremex or horntails.

Campoletis argentifrons (Cress.) are only about 1/8 inch long, black-bodied (except outer half of abdomen which is reddish-brown) and are important parasites of cutworms and the corn earworm.

Bathyplectes curculionis is about 1/16 inch long with a black, robust body. Females lay eggs in alfalfa weevil larvae (only host). Wasp larva that hatches from the egg feed internally, slowly devouring the weevil larva. This parasitoid, not available commercially, occurs virtually everywhere in alfalfa fields.

Ophion spp. are most common with yellow or brownish bodies and the abdomen slender in front, arches, compressed from side to side, ovipositor short and body length 5/6 inch long. They are common in May (late spring) and are attracted to lights. They parasitize certain caterpillars and white grubs. If handled carelessly, the ovipositor can penetrate the skin much like a pin prick.

Gambrus nuncius (Say) are about 5/16 inch long, reddish-black (basal half of abdomen reddish and rest black with a whitish yellow mark at the tip in females). The first segment of the male abdomen is black. This parasite attacks caterpillars of swallowtail butterflies.

Braconid Wasps

Adults are relatively small which measure about 1/16 inch long, more stout-bodied than ichneumon wasps with the abdomen almost as long as the head and thorax combined. The abdomen is always short (not compressed at the sides) and the ovipositors are usually shorter than the body. They are attracted to lights and flowers.

Cremnops vulgaris (Cress.) is about 5/16 inch long with the head, antennae, wings and parts of the legs and space on the back, between the hind wings, shining black. The rest of the body is reddish-brown or orange. This species is common and a parasite of the garden webworm.

Chelonus texanus Cress. is about 3/16 inch long, clear winged, black-bodied, legs alternately black and brownish with a brown spot on each side forward of the abdomen. Wing veins are yellowish brown with a black stigma. It is common in alfalfa.

Lysiphlebus testaceipes (Cresson) is 1/16 inch long, shining black, smooth thorax, brownish-black abdomen and honey-yellow petiole (narrow forward part of abdomen) with 13 segmented antennae in females and 14 in males. It is an important parasite of aphids such as corn leaf aphid, greenbug, melon and cabbage aphid. Females deposit a single egg in an aphid with the young parasite devouring the internal tissue, causing the aphid to become brown, swollen and attached to a leaf. Later, the parasite emerges through a circular opening in the aphid.

Apanteles congregatus (Say) are less than 1/8 inch long, black colored with yellowish legs and clear wings. This tiny wasp parasitizes cutworms, tomato hornworms and other kinds of caterpillars. Cottony masses of white cocoons, frequently found on the ground in hay or grain fields, are erroneously believed to be "eggs." Often parasitized tomato hornworms are seen covered with numerous white cocoons.

A. militaris (Walsh) are slightly larger, legs are brown, cocoons white with a brownish tinge and are important armyworm parasites.

Bracon gelechiae Ashm. are about 1/16 inch long with the head and thorax black marked with yellow, abdomen dull black (rough-surfaced) with yellow, parasitizes the strawberry leafroller, eastern tent caterpillar and other moth larvae.

Chalcid Wasps

Adults are nearly all very small, with some quite minute, measuring 1/64 to 5/16 inch long with fewer wing veins than most other wasps and wings are not folded when at rest. Some have clear wings and others no wings at all. Antennae are elbowed with up to 13 segments and the hind femora of the legs are much swollen in some species.

Brachymeria ovata (Say), between 3/16 to 1/4 inch long, black and yellow bodied (hind femora black with a white or yellow spot at the tips), abdomen globular-shaped, surface smooth, parasitizes the strawberry leaf roller and other hairy caterpillars.

Trichogramma minutum Riley about 1/64 inch long, wings are fringed with hairs, yellow-brownish abdomen and pink eyes, parasitizes eggs of many insect pests such as the cotton bollworm, spruce budworm, corn earworm and southern cornstalk borer. Trichogramma wasps sold commercially are parasites of cabbleworm, tomato hornworm, corn earworm, codling moth, cutworm, armyworm, webworm, cabble looper, corn borer and almost all moth and butterfly eggs that hatch into worm pests.

Females lay from one to fifty eggs which are deposited in a single host egg (25 at a time, depending on host size). Host eggs turn black with the newly hatched wasp larva moving within the host egg, killing the embryo. Larvae hibernate in the host egg with the number of broods varying from 13 to 50, depending on climate.

Aphelinus mali are about 1/15 inch long, dark brown to black with the base of the abdomen yellow, legs and antennae partly yellow. One or more eggs are deposited in the body of an aphid, but only one develops into a mature wasp. Larvae, as an internal parasite, consumes all but the skin. Body juices ooze from the aphid, gluing it to the twig. Aphid shells become black and mummified. Pupation occurs in the host with the adult emerging by cutting a hole in the top of the "mummy." The life cycle is about 30 days. Hosts include woolly apple aphids, cabbage aphids, greenbug, rose aphids and other aphids.

Evaniid Wasp

Adults are about 1/4 to 1/3 inch long, but differ from other wasps in having the abdomen attached near the top part of the thorax instead of down below. The abdomen is very small and carried almost like a "flag." These wasps are entirely black or black and red, clothed with a fine pubescence. They are parasitic in the egg capsules of cockroaches. Wasp eggs are deposited in the roach egg capsules before they harden. One egg is inserted within one roach egg in the single capsule. The larva feeds within a single egg and later, as it matures, attacks other roach eggs within the capsule.

Cuckoo Wasp

Adults are about 1/4 to 1/2 inch long and brilliant metallic colored in shades of green, blue, red or purple with the body coarsely sculptured. When these wasps are disturbed, they curl the body into a ball with the wings protruding to the sides. This is believed to be a way of feigning death for protection. They lay eggs in exposed cells or nests of mud daubers and potter wasps. They hibernate as larvae and pupate in the host nests.

Potter Wasp

Eumenes fraternus Say is about 3/4 inch long entirely black or black with yellow or white markings scattered. These solitary wasps construct small marble-sized or vaselike mud pots often fastened to window screens or climbing vines on sides of houses. Nests are provisioned with several paralyzed caterpillars with an egg laid. The hatching larva consumes the caterpillar.

Control Measures

Parasitic wasps are normally not a problem in and around the home. Some are attracted to lights and others may enter through windows, doors and other small openings. Use proper light discipline, avoiding lights left on 24 hours per day, if practical. Use special yellow lights (high-pressure sodium vapor), which are least attractive to insects. Be sure to caulk and seal any cracks and openings into the home. Live individuals can be collected by broom and dustpan and relocated outdoors far from the house, since they are beneficial to agriculture. If they are bothersome, an aerosol can of pressurized spray, containing pyrethrins, will give good knockdown of nuisance insects where they can be collected and discarded. Before using any pesticide, always read the label, follow directions and safety precautions.

This publication contains pesticide recommendations that are subject to change at any time. These recommendations are provided only as a guide. It is always the pesticide applicator's responsibility, by law, to read and follow all current label directions for the specific pesticide being used. Due to constantly changing labels and product registration, some of the recommendations given in this writing may no longer be legal by the time you read them. If any information in these recommendations disagrees with the label, the recommendation must be disregarded. No endorsement is intended for products mentioned, nor is criticism meant for products not mentioned. The author, The Ohio State University and Ohio State University Extension assume no liability resulting from the use of these recommendations.