Major Groups of Natural Enemies: Parasitoids, Part V

In this final article in our series on the groups of natural enemies of insects and mites I will discuss a number of families of parasitic wasps. In previous articles, I discussed some of the more important groups in biological control, namely the wasp families Ichneumonidae and Braconidae, and the various families of chalcid wasps. Although nearly 25 other wasp families contain parasitoids, relative to the previously discussed families, these groups have been less important in natural and biological control of pests. However, they do play a role in the overall regulation of pest populations, and some individual species are very important in biological control. As in previous articles, the organization of this article will be along taxonomic lines; related families will be grouped within their respective superfamilies.

There are three families in the superfamily Cynipoidea. The largest family, with over 600 species in the U.S. and Canada, is the Cynipidae, which is commonly called the gall wasp family. Gall wasps are generally quite small, usually less than a few millimeters in length. These insects are plant-feeders in the larval stage, causing abnormal growths, called galls, on leaves or stems; the larvae feed within these galls. Although these insects are not themselves parasitic, they account for some very biologically-interesting relationships that include parasitoids. The galls created by cynipids (such as on oak trees) are frequently inhabited by other wasp larvae. Some of these are just taking advantage of the resources provided by the gall, and they co-exist with the larval cynipid; these are called inquilines. However, both the gall wasps and their inquilines are frequently parasitized by other wasp species, which, in turn, may also be parasitized by yet other species. It is not unusual for four, five, or even more species of these tiny wasps to emerge from a large oak gall created by just a single species of gall wasp.

Two other groups are very closely related to the gall wasps; some people consider these to be in sister families, while other scientists contend that they are closely enough related to be considered subfamilies of the Cynipidae. The eucoilid wasps, of which there are about 80 species in our part of the world, are mostly all parasites of the pupae of various types of flies. Some species are relatively common parasites of fly maggots that occur in manure and carrion; at least one species has been established in the southwestern United States for classical biological control of such pests. There are only about 30 species of charipid wasps in the U.S.; these are all hyperparasitoids; that is they parasitize other parasitoids usually the braconids and chalcids that parasitize aphids.

Also within the Cynipoidea are the two small families Figitidae and Ibaliidae. Figitid wasps parasitize the pupae of lacewings and the larvae and pupae of flies. Some species parasitize pest flies (such as dung-breeding species) while others parasitize beneficial flies, such as predatory hover (syrphid) flies. Ibaliid wasps are the largest species in the superfamily, with some over a half inch long. There are only a few species, and generally not common. They parasitize the larvae of horntails, which are woodborers.

Members of the small (less than 60 known species in the U.S. and Canada) superfamily Evanioidea are all parasitoids of other insects. Members of the family Evaniidae are all parasitoids of cockroach eggs; some species are fairly common in human habitations that are infested with cockroaches. Gasteruptiid wasps are parasitoids of the natural enemies of solitary bees and wasps. Aulacid wasps are parasites of the larvae of wood-boring insects.

The superfamily Pelecinoidea is represented by a single species in North America, in the family Pelecinidae. Pelecinus polyturator is a large, spectacular parasite of the white grub larvae of June beetles (Phyllophaga spp.). It is a relatively common species through much of the Midwest. Females are jet black, two inches long, with a very long, slender abdomen. Males are very rare.

The Proctotrupoidea is a fairly large superfamily; all known members are parasitoids. There are about eight families in total, but some of these have only one or two species and are quite rare and therefore will not be covered. The families Proctotrupidae (also known as the Serphidae not SYRPHIDAE, which is a family of flies), Ceraphronidae, and Megaspilidae are all fairly small, but members are non uncommonly found during general insect collecting. Not much is known of their biologies, but some are parasites of the larvae of beetles, flies, or other hosts; some are hyperparasites. Diapriid wasps are fairly common, with over 300 species known; most are parasites of fly larvae. From a biological control perspective, the families Platygastridae and Scelionidae are the most important in this group. Platygastrid wasps are also fairly common; they parasitize gall midges, mealybugs, and whiteflies. Platygaster hiemalis is an important native parasite of the introduced wheat pest Hessian fly. Three species of Allotropa (two native and one intentionally introduced) are important parasites of Comstock mealybug in the eastern United States. All scelionid wasps are parasitoids of the eggs of other insects and spiders. The eggs of grasshoppers, praying mantids, and stink bugs are commonly parasitized.

Most of the wasps in the superfamily Bethyloidea (or Chrysidoidea) are parasitoids of other insects. The family Chrysididae includes the cuckoo wasps. These are medium-sized, stout-bodied insects, somewhat resembling the shape of small bees. They are usually metallic blue, green, or red in color and they curl up into a ball when disturbed (kind of like tiny winged gazing balls!). Some are inquilines in bee or wasp nests but others parasitize sawfly larvae or the eggs of walkingsticks. Bethylid wasps, of which there are about 100 species in the U.S., are primarily parasitoids of the larvae of moths and beetles. Several species are important in the biological control of forest pests such as hickory shuckworm and Nantucket pine tip moth. Carpenter ants are also parasitized by bethylids. Laelius pedatus has been researched for augmentative biological control of pests of stored products, but I have not yet seen that it has become commercially available. Members of the family Dryinidae are primarily parasites of nymphs and adult leafhoppers, planthoppers, and treehoppers, but they are not at all common and probably have little if any benefit in pest management.

Some of the wasps in the superfamily Scolioidea are amongst the largest of all parasitoids. Contrary to most groups of parasitic wasps, females of this group are capable of using their ovipositor as a stinger for defensive purposes. Some, such as members of the velvet ant family (Mutillidae) are notorious for their highly painful stings. Velvet ants are densely clothed in often brightly colored hairs (yellow, orange, red, or white, often with black bands) which serve as warning coloration. Females are wingless. They parasitize the larvae of ground-nesting bees and wasps. Closely related to the velvet ants is the family Tiphiidae, whose members are usually brown or black and sparsely hairy. Tiphiid wasps parasitize larval insects found in the soil and in rotting wood; many are parasites of serious pests such as white grubs. Tiphia intermedia is a common species that parasitizes June beetle (Phyllophaga) larvae. Tiphia vernalis and T. popilliavora were previously discussed in MBCN as parasitoids of Japanese beetle grubs. Many scoliid wasps are quite large, some up to two inches in length. They are often brightly marked with yellow and black warning coloration. These, too, are parasitoids of white grubs; many attacking the larvae of June beetles.

- Dan Mahr, University of Wisconsin - Madison

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