|
Oklahoma State University Stillwater, OK |
|
Oklahoma Alfalfa |
|
|
|
Oklahoma State University Stillwater, OK |
|
Oklahoma Alfalfa |
|
Beneficial Insects - Predators |
|
|
It is fortunate for alfalfa growers that many of the insects found in this crop are natural enemies that attack the plant-feeding insect species. Although natural enemies do not typically maintain populations of some insect pests such as the alfalfa weevil below economic threshold levels, others such as aphids and foliage-feeding caterpillars are effectively controlled in most years. The need for insecticide applications would be increased greatly were it not for the presence of these natural enemies. A second group of beneficial insects that are of critical importance in alfalfa seed production is the pollinators. Without pollination by several species of bees, seed production in alfalfa is not profitable. Predators of Insects Most well-known among the predators are the lady beetles, a group in which both larvae and adults prey upon a variety of insects, most commonly on aphids and small stages of foliage-feeding caterpillars. They also eat larvae of the alfalfa weevil. Species that are most common in alfalfa have an oval body shape and are usually bright orange and black in color. Among them is an imported species called "C-7" or the seven-spotted lady beetle which has become abundant throughout Oklahoma. The larvae of lady beetles typically have elongate bodies with long legs and orange and black mottled coloration. Laboratory studies have shown that individual lady beetle adults and larvae consume 20-30 aphids/day. Also common in alfalfa are the aphid lions or larvae of the lacewings. Aphid lions resemble tiny alligators with long, curved, hollow jaws which they use to clamp onto insect hosts and suck out body fluids. These predators readily attack not only aphids, but foliage-feeding caterpillars as well. Adult lacewings are typically brown or green in color, with large, fragile wings. The damsel bugs are slender bodied insects with gray to tan coloration. Their front legs are adapted for grasping prey, and they possess piercing-sucking mouthparts which they use to suck body fluids from their prey. Damsel bugs attack any small insects they encounter including aphids, Lygus bugs, weevil larvae, and small caterpillars. There is also a variety of spiders in alfalfa which prey upon insects. The most effective of these are the crab spiders which search for prey in the foliar canopy without use of webs. Recent studies have indicated that these spiders may be quite important as natural enemies of insects in field crops.
|
|
| Richard Berberet,
Alfalfa Entomologist Department of Entomology and Plant Pathology Oklahoma State University |
 |
