Biological Control of Insect and Weed Pests in North Dakota Agriculture (continued - part 2 of 4)

E-1225, January 2002

Contents

Introduction
Biological Control
        - Parasites
        - Predators
        - Diseases
Maintaining Natural Order
        - Canola Insect Pests
        - Potato Insect Pests
        - Sunflower Insect Pests
        - Sugarbeet Insect Pests
        - Corn Insect Pests
       - Small Grain Insect Pests
Weeds
       - Leafy Spurge
       - Purple Loosestrife
Conclusions
Biological Control References

Predators include birds, fish, amphibians, reptiles, small mammals, and arthropods. Arthropods (insects, mites and spiders) are the most important predators in pest management and include lady beetles, ground beetles, syrphid flies, green lacewings, assassin bugs, predaceous bugs, minute pirate bugs, predatory mites, and spiders. Predators are usually larger than the prey which they capture and kill. They may use camouflage to "sit and wait" for prey or may be active hunters. Predators usually deposit their eggs near their prey so the immatures can immediately find their host and begin feeding. Immature stages are mobile, usually consume more than one prey during their development, are often generalist feeders (more than one species of host is attacked), and usually both the adults and immatures feed on the prey insect.

Many of the true bugs are predatory insects. They are predaceous as nymphs and adults, are very active hunters, and have a varied diet. Their prey range from insect eggs, young caterpillars, aphids and spider mites to other plant bugs. Common members of this group are the minute pirate bug (Figure 3) and flower bug, Orius tristicolor and O. insidiosus, which are abundant throughout North America. These small (1/8 inch) black and white insects overwinter as adults. The nymphs are a yellow-orange color. Both stages feed on aphids, insect eggs, thrips, and young caterpillars. Several species of damsel bugs (Nabis spp., Figure 4) are common predators throughout the region. These predators are � inch or less in size, and range in color from mottled brown to black. They feed on insect eggs, numerous caterpillars, aphids, and plant bugs. The twospotted stink bug, Perillus bioculatus (Figure 5), is one of the species of stink bugs found in the region. Adult stink bugs are � inches long. They attack slow moving prey, including some major insect pests, such as larvae of the Colorado potato beetle and sunflower beetle. They also consume numerous species of caterpillars.

Figure 3. Minute pirate bug, Orius trsticolor. (Click here for a 21KB color photo of a minute pirate bug.)




Figure 4. Damsel bug, Nabis spp.  (Click here for a 22KB color photo of a damsel bug.)





Figure 5. Twospotted stink bug, Perillus bioculatus. (Click here for a 21KB color photo of a twospotted stink bug.)

Assassin (Figure 6) and ambush bugs (Figure 7) are medium sized insects, ranging in size from � to 1� inches. They are green, brown to black, with some species having red or orange markings along the body margins. Their first pair of legs is enlarged for capturing prey. They have powerful beaks used to impale their prey and suck out the body fluids.

Figure 6. Assassin bug. (Click for a 31KB color photo of an assassin bug.)

Figure 7. Ambush bug. (Click for a 23KB color photo of an ambush bug.)

The adult and larval stages of many beetles are insect predators, and they can be found in varied habitats. They may be found living in the soil, on the soil surface, or on plants. They may feed on all types of insects, other arthropods, and slugs and snails. Their prey may be varied or specific. The carabid, or ground beetles, range in size from 1/8 to 1� inches long. They have flattened bodies and range in color from black to iridescent blue or green. They are recognized by their prominent jaws. Their worm-like larvae live in the soil. Adults seek prey on or beneath the soil; some species climb plants in search of prey. Lady beetles include numerous species, are common predators of aphids and other small insects and insect eggs, and many of the adults are readily recognized (Figure 8). Often brightly colored red and orange and bearing spots, the adults can also be brown or black with spots. The larvae (Figure 9) are elongate and taper from the head to the tail. Their color varies and they may be black, brown, or dark blue, with bright spots or stripes on their back. The eggs are yellow and laid in clusters on the undersides of leaves.

Figure 8. Lady beetle adult. (Click for a 16KB color photo of a lady beetle adult.)

Figure 9. Lady beetle larva. (Click for a 12KB color photo of a lady beetle larva.)

Lacewing adults (Figure 10) are fragile-looking insects with four lace-patterned wings. They are green or brown and about 1 inch long. Their eggs are laid singly on top of a slender stalk attached to a plant. The elongate, flat, mottled brown larvae (Figure 11) move quickly over the plant in search of prey. They have large, sickle-shaped mandibles that they use to capture and hold prey as they suck out the body fluids. The larvae feed on many soft bodied insects, chiefly aphids, as well as small caterpillars, insect eggs, and mites. They are most abundant later in the season.

Figure 10. Green lacewing adult. (Click for a 24KB color photo of a green lacewing adult.)

Figure 11. Green lacewing larva. (Click for a 24KB color photo of a green lacewing larva.)     

Hover flies (Figure 12) are bee-like, with yellow and black bands that ring the abdomen. They can be seen hovering around flowers where they feed on nectar and pollen. The predatory larvae (Figure 13) are legless, slug-like maggots, often pale green in color. They are voracious predators of aphids.

Figure 12. Hover or syrphid fly.  (Click for a 20KB color photo of a hover fly.)

Figure 13. Syrphid fly larva. (Click for a 19KB color photo of a syrphid fly larva.)

All spiders are predaceous and are generalist feeders. The size and color of spiders vary considerably depending on the group they belong to. Wolf spiders are colored to blend in with the soil since that is where they search for prey, whereas the crab spiders (Figure 14) are often the color of their background, such as leaves or flowers. Their methods for capturing prey are varied, ranging from web spinning to active hunting. All stages of insects are consumed by spiders.

Figure 14. Crab spider feeding on moth. (Click for an 18KB color photo of a crab spider.)

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E-1225, January 2002