Feature Article

The Major Groups of Natural Enemies:
Predators, Part III

Editor's Note: As we have written in past issues of MBCN, there are three general groups of natural enemies of pest insects and mites: predators, parasitic insects, and insect pathogens (some would include entomogenous nematodes as a separate fourth group). Although we have highlighted specific natural enemies, or specific groups, in our monthly Know Your Friends column, we haven't yet given a broader overview of the major groups. This is the third of a series of feature articles that addresses this topic. Further information on these groups can be found in North Central Regional Extension Publication 481, Biological Control of Insects and Mites.

In September's feature article, the lady beetles and ground beetles were discussed. This month's article continues looking at the beetles, specifically some smaller or lesser known families.

Rove beetles-Family Staphylinidae. The rove beetle family is very large, with more than 20,000 species. They are mostly small to tiny, slender, and often black in color. The elytra (the first pair of wings in the beetles, which are hardened to cover and protect the beetle's abdomen) are very short in the rove beetles, so that several abdominal segments are exposed. Many species are nocturnal, and many are found associated with the ground, such as under leaf litter or stones, or in loose soil. Some rove beetles apparently are scavengers, but many are general predators, in both the adult and larval stages. Some have been shown to be important natural enemies of the eggs and larvae of flies that breed in manure or similar habitats. Some types occur in vegetation where they prey on plant pests.

Checkered beetles-Family Cleridae. These beetles are often highly colored with intricate patterns. They are small to medium in size (usually 1/4 inch or less), often cylindrical and usually hairy. The adults are found under bark and on flowers. About 250 species are known from our region and some 2500 for the whole world. Larvae, with few exceptions, feed primarily on insects destructive to bark and wood, such as the larvae of bark beetles and longhorned beetles. They are generally considered important in the natural control of forest pests.

Hister beetles-Family Histeridae. These are polished, hard, flattened, and usually broadly oval beetles, usually less than 1/2 inch long, usually black in color and usually with shortened elytra (wing covers) that expose the terminal couple segments of the abdomen. Many have very obvious forward-projecting mandibles. Different species occur in different habitats. Some frequent carrion, dung, or other rotting organic matter where they are predaceous on scavengers such as maggots. Other species are found under the bark of trees or in burrows of wood-infesting insects. Their most important role in biological control is probably as predators of wood boring tree pests and filth flies. The larvae are also predators. More than 3,000 species are known, with 500 in North America.

A few additional families have some beneficial impact as natural enemies of pests. However, little work has been done in trying to manipulate these for biological control. All of the species in the following four families of beetles are predaceous in the larval stage, living primarily on the ground.

Fireflies-Family Lampyridae. The nocturnal larvae of the familiar "lightening bugs" feed chiefly on snails and slugs; other prey of this family includes earthworms, cutworms, leaf beetle larvae and various other soft-bodied insects. Luminescent larvae are often called "glow-worms," a name also used for larvae of the following family. The adults use their flashing lights in the mating process. Over 2000 species have been described, with 60 in North America. The larvae prefer damp places and are inactive by day. Mollusk feeders live in moist habitats. Other species are found under debris on the ground, beneath bark, stones or decayed vegetation where considerable moisture exists.

Glowworms-Family Phengodidae. These somewhat uncommon beetles closely related to fireflies. The short-lived, nocturnal males often have feathery antennae. The wingless, luminescent females, which are very larva-like in appearance, give rise to the common name. They range up to about 1 inch in length and are found on foliage or on the ground. The nocturnal larvae generally occur in forests beneath decaying logs and in leaf litter, the typical habitat of the millipedes they feed on. Although they are specialist predators of millipedes, they will feed on soft-bodied insects or other invertebrates. This is a small family of about 170 described species which occur mainly in the tropical regions of the Western Hemisphere. However, they are fairly commonly seen throughout the Midwest, with about 30 species occuring in North America.

Netwinged beetles-Family Lycidae. Only 50 species of netwinged beetles are known in North America. The adults of these soft-winged beetles are somewhat similar in appearance to fireflies and soldier beetles, but have a network of raised veins on the elytra (wing covers). They are active in the day and feed on juices from decaying plant material or occasionally on other insects. The larvae feed on a diversity of soft-bodied insects and snails or slugs.

Soldier beetles-Family Cantharidae. Adult soldier beetles are elongate, soft-bodied beetles similar to fireflies. They are usually found on flowers, and some species have been observed feeding on aphids and other soft-bodied insects. The larvae of most species are predaceous on other insects, including eggs of grasshoppers, small caterpillars, maggots and other soft-bodied insects. Some are omnivorous, feeding to some extent on plant tissue such as wheat grains and vegetables. Some 1500 species are known in the world but there are less than 200 in the U.S.

Several other families of beetles are entirely or partly comprised of species which are predatory. Some families live in or near bodies of water, and some of these, such as predaceous diving beetles (Family Dytiscidae) may have an impact on the populations of mosquitoes and other pests that spend time in the water. In addition to these, the following groups of terrestrial beetles may occasionally help reduce populations of plant pests, but there have been few attempts to use these in biological control.

Flat bark beetles-Family Cucujidae. Most species are predaceous on mites and soft bodied insects found under bark of dead or dying trees or under debris on the ground. Some species are destructive to stored products. A few species are parasitic on larvae of wood inhabiting insects, such as the larvae of longhorned beetles.

Click beetles-Family Elateridae. Wireworms, the larvae of click beetles, live in soils, decaying vegetation, under bark and other situations where they are not exposed to light. There are many destructive species, and many others are scavengers. However, many species are predaceous, feeding on insects and other invertebrates.

Blister beetles-Family Meloidae. The larvae of many species feed on grasshopper eggs. The adults of some species are occasionally plant pests.

Softwinged flower beetles-Family Melyridae. Both the adults and larvae of many species are predaceous, feeding on eggs, larvae and soft-bodied insects, especially wood boring species. In the southwestern United States, members of the genus Collops are frequent predators found in alfalfa and other field crops, where they are considered to be a fairly important component of the complex of generalist natural enemies.

Carrion beetles-Family Silphidae. The larvae are largely scavengers, but some are predaceous on snails; others prey on maggots that occur in decaying organic matter.

- Dan and Susan Mahr, University of Wisconsin - Madison

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