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 first 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.
A dictionary definition of predation would say something like "a way of life in which the primary source of food is obtained by the catching, killing, and eating of other animals." When dealing with pest arthropods, important predators include vertebrate animals, such as birds, bats, frogs, rodents, and fish, and invertebrate animals, which primarily include predatory arthropods, especially insects, but also spiders and some groups of mites. Predatory arthropods may further be characterized as follows: often as large or larger than their prey; often fast-moving and having good searching capabilities; often with some mechanism for catching and subduing their prey, such as a web, modified (raptorial) legs, or paralytic saliva; and usually requiring many prey during the course of their growth and development. The predatory way of life may occur in only one life stage (such as the larval stage of flower flies) or throughout all active stages (such as in the pirate bugs). Some predators have complex development (complete metamorphosis, with egg, larva, pupa, and adult stages); others have simple development (incomplete metamorphosis), with egg, nymph, and adult stages. Some predators have chewing mouthparts whereas others use a sharp beak to suck fluid from their prey.
There are many dozens of families of insects that contain one or more predatory species; in some of these families all species are predatory. Many predators are important in the general "balance of nature" but are not important in agricultural pest management. For example, within the group of insects we call the true bugs (Order Hemiptera) there are about a dozen families of predators that live in, on the surface of, or on the shore of bodies of water, where they prey on insects and other small animals. Although no one has taken a census of all the species of predatory arthropods important in agriculture, the number would likely reach into the thousands. For example, there are about 400 North American species in the ladybird beetle family alone. The impacts of some species of predators found in agriculture are probably minor, whereas many species have repeatedly been shown to be important in many crop systems. Most predators are considered to be "generalists" in that they will capture and eat most anything that they can find within the range of habitats that they live. Some groups tend to specialize, such as the ladybird beetle genus Stethorus, which feeds on spider mites. The adults of many important predators require alternative foods, or can subsist on supplemental foods, especially flower nectar and pollen.
This month's article will focus on two orders of predatory insects: the praying mantids and the true bugs.
Praying mantids-Order Mantodea. Praying mantids (or mantises) are among the most recognizable of predaceous insects; they are easily identified by their slender body, long slender middle and hind legs, large, grabbing (raptorial) front legs, and rather sinister-appearing head with large bulging eyes. Mantises occur in most states in the U.S., but their abundance decreases in more northern areas of extreme cold winters. All mantises are predatory on other insects. Most are highly generalist, opportunistic predators, readily capturing anything of an appropriate size that comes within reach, including pollinators and other beneficial insects. Further, they tend to be cannibalistic and are rarely found in large enough numbers to have a significant impact on pest populations. Mantid egg cases are available from some commercial suppliers of beneficial insects, but should be viewed more as a curiosity and a good lesson in natural history than as an effective biological control.
True bugs-Order Hemiptera. The true bugs consist of insects with simple metamorphosis and piercing-sucking mouthparts. Some are pests of crops, some are aquatic predators, a few are blood feeders (such as bed bugs), any many are predators of terrestrial insects, including crop pests. Most of the predatory types have this feeding behavior as both nymphs and adults. Members of the following six families are important as predators of crop pests.
Minute pirate bugs-Family Anthocoridae. ("Minute" here refers to the very tiny size of these insects, not 1/60th of an hour.) These are very tiny insects, the adults measuring only 1-2 mm in size. They feed on mites, insect eggs, and small insects. They occur in many types of agricultural crops and are commonly found in home gardens. Members of the genus Orius are generally considered to be very important in biological control. Some minute pirate bugs reside in stored-grain bins where they feed on stored-product pests. More information on minute pirate bugs.
Plant bugs-Family Miridae. Within the family Miridae are both plant pests and predators. Plant bugs are generally small, 3-6 mm in length. Members of the genus Lygus are the tarnished plant bugs which are important pests of many crops. Many species of plant bugs, however, are primarily predatory, and are commonly found in crops, orchards, forests, and home gardens. Predatory species feed on mites, insect eggs, and small insects such as aphids, whiteflies, and small caterpillars.
Assassin bugs-Family Reduviidae. Most assassin bugs are beneficial predators of pests of the farm, forest, or garden. These are relatively large insects, with adults measuring 1/3-1" in length. They have raptorial front legs and substantial beaks that are used for capturing, subduing, and feeding on prey. They can feed on quite large caterpillars and other insects. One group of assassin bugs are the ambush bugs (sometimes considered as a separate family, the Phymatidae). Ambush bugs can be found on vegetation, and are frequently seen sitting in flowers waiting for prey. They are very stout-bodied, tan-colored with darker markings, and have very powerful raptorial front legs. Assassin bugs can inflict a painful bite if handled, resulting in an inflammation that may persist for a few days. More information on assassin bugs.
Seed bugs and bigeyed bugs-Family Lygaeidae. These insects are superficially similar to the plant bugs, being about the same size and shape. The family consists of both plant feeders (many of which feed on fruits or seeds) and predators. The bigeyed bugs, members of the genus Geocoris, are predators that occur in many habitats, including fields, gardens, and turf grass. Bigeyed bugs feed on mites and small insects. They are common predators in turf grass, where they feed on chinch bugs, sod webworms, and other pests.
Damsel bugs-Family Nabidae. Damsel bugs are generalist predators that are intermediate in size and appearance between plant bugs and assassin bugs. Members of the genus Nabis are probably the most common species in Midwestern crops. These are rather slender insects, tan in color, with slightly raptorial front legs. Nabis is one of the most common predators in alfalfa fields, but it occurs in most types of crops as well as home gardens. They feed on many types of pests, ranging from mites and aphids to small caterpillars and beetles. More information on damsel bugs.
Stink bugs-Family Pentatomidae. Stink bugs are medium sized, reaching to 3/4" or more in length. They have a broad, shield-shaped body, and are usually green or brown (although some are more brightly colored). When disturbed, they can discharge a foul and penetrating odor, which helps them avoid larger predators. Many stink bugs are plant feeders and a few can be significant pests of crops. Some stink bugs are predatory; the species Perillus bioculatus (the twospotted stink bug) and Podisus maculiventris (the spined soldier bug) are very important in biological control. Nymphs and adults of both species feed on caterpillars, beetle larvae and adults, and other medium-sized insects. Both are common predators of Colorado potato beetle larvae. These species have been at times commercially available in the United States.
In a future issue of MBCN, we will continue with other groups of predators, including lacewings, beetles, and flower flies.
- Dan Mahr, University of Wisconsin - Madison
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