Principal Insect Predators

Spiders. Spiders are among the most neglected and least understood of predators. They rely on a complex diet of prey and can have a strong stabilizing influence on them. Because spiders are generalists and tend to kill more prey than they actually consume, they limit their preys' initial bursts of growth.

Many spiders live in crop canopies but most inhabit the soil surface and climb plants. Fields with either living plants or residue as soil cover tend to harbor diverse and abundant spider populations. Up to 23 spider families have been documented in cotton and 18 species have been tallied in apples. Because such diverse populations of spiders remain relatively constant, they maintain tolerable levels of their associated prey without extinguishing them.

Fields with either living plants or residue as soil cover tend to harbor diverse and abundant spider populations. Living mulches composed of clover or other soil plant covers attract spiders, while residue from plants like barley or rye also harbor spider populations.

Lady beetles (Coccinellidae, also called ladybugs or ladybird beetles). With their shiny, half-dome bodies and active searching behavior, lady beetles are among the most visible and best known beneficial insects. More than 450 native or introduced species have been found in North America. They are easily recognized by their red or orange color with black markings, although some are black with red markings and others have no markings at all.

Lady beetles have been used in biological control programs for more than a century and are beneficial both as adults and larvae. Most larvae are blue-black and orange and shaped like little alligators. Young larvae pierce their prey and suck out their contents. Older larvae and adults chew entire aphids.

Any crop prone to aphid infestation will benefit from lady beetles, even though this predator's vision is so poor that it almost has to touch an aphid to detect it. Growers of vegetables, grains, legumes, strawberries and orchard crops have all found lady beetles helpful in managing aphids. In its lifetime, a single beetle can eat more than 5,000 aphids. In the Great Plains, studies of greenbug pests in grain sorghum have shown that each lady beetle adult can consume almost one of these aphids per minute and dislodge three to five times that many from the plant, exposing the dislodged greenbugs to ground-dwelling predators.

While their primary diet is aphids, lady beetles can make do with pollen, nectar and many other types of prey, including young ladybugs. Indeed, their extensive prey range — which includes moth eggs, beetle eggs, mites, thrips and other small insects — makes lady beetles particularly valuable as natural enemies.

Ground beetles (Carabidae). Predaceous ground beetles, or carabids, belong to a large family of beneficial beetles called the Carabidae whose adults live as long as two to four years. Several thousand species reside in North America alone.

Generally nocturnal, most predaceous ground beetles hide under plant litter, in soil crevices or under logs or rocks during the day. At night, their long, prominent legs allow them to sprint across the ground in pursuit of prey. Some species even climb up trees, shrubs or crops.

Most adult ground beetles range in length from 0.1 to 1.3 inches (3.232 mm). Their antennae are fairly threadlike and their bodies — although quite variable — are often heavy, somewhat flattened and either slightly or distinctly tapered at the head end. Some species are a brilliant or metallic purple, blue or green, but most are dark brown to black.

Armed with large, sharp jaws, adult predaceous ground beetles are ferocious. They can consume their body weight in food each day. Some cara-bids grind and eat such annual weed seeds as foxtail and velvetleaf. Larval carabids are not always predatory. In the Lebia genus, for example, adults are predators but first-instar larvae are parasites of chrysomelid beetles. (Instars are stages between successive molts.) Normally colorful, Lebia adults are just 0.1 to 0.6 inches (2.5-14 mm) long. Lebiagrandis is a native and specialist predator of all immature stages of the Colorado potato beetle in cultivated potatoes in the eastern and mideastern U.S.

Lacewings (Chrysoperla spp.). Green lacewings — with their slender, pale-green bodies, large gauze-like wings and long antennae — are very common in aphid-infested crops, including cotton, sweet corn, potatoes, tomatoes, peppers, eggplants, asparagus, leafy greens, apples, strawberries and cole crops.

The delicate, fluttering adults feed only on nectar, pollen and aphid honeydew. About 0.5 to 0.8 inches (12-20 mm) long, they are active fliers — particularly during the evening and night, when their jewel-like golden eyes often reveal their presence around lights.

The larvae — tiny gray or brown "alligators" whose mouthparts resemble ice tongs — are active predators and can be cannibalistic. Indeed, green lacewing females suspend their oval eggs singly at the ends of long silken

COVER CROPS SARE-funded researchers in Georgia seeking new

LURE BENEFICIAL ways to raise healthy cotton — traditionally one

- of the most pest-plagued, thus one of the most

INSECTS' IMPROVE chemically treated commodities — focused on

BOTTOM LINE attracting insects that prey on damaging pests.

IN COTTON A group of scientists from USDA's Agricultural

- Research Service, the University of Georgia, and

Fort Valley State University planted a variety of flowering cover crops amid cotton rows to test whether their blooms would bring earworm- and budworm-killing predators to minimize the need for insecticides.

Working on seven mid- and southern Georgia cotton farms, the team eliminated one insecticide application by planting legume cover crop mixes that brought predators like the pirate bug, big-eyed bug and fire ants to prey on damaging worms. Using conservation tillage to plant cotton amid the cover crops also improved yields — on average, 2,300 pounds of seed cotton compared to 1,700 pounds on control plots. (Seed cotton weight includes lint and seed before cleaning.)

Growing a mix of balansa clover, crimson clover, and hairy vetch prolonged cover crop flowering from early March through late April and had the added benefit of out-competing weeds. "With this range of blooming, we're able to start building the beneficial populations early in the season," said Harry Schomberg, an ARS ecologist and project leader. "Reducing one application of insecticides could be pretty substantial on a larger scale like 100 acres." Glynn Tillman, an ARS entomologist who collaborated on the project, found that predator bugs moved from the cover crops into the cotton early in the season, providing more worm control. Moreover, the conservation tillage and cover crop residue resulted in more beneficial soil organisms that likely contributed to better cotton yields.

To demonstrate their results, the team went beyond holding field days. Tillman introduced the promising cotton-cover crop-conservation tillage system to hundreds of thousands attending the Sun Belt Ag Expo in Moultrie, Ga. "It was stalks to protect them from hatching siblings. Commonly called aphid lions, lacewing larvae have well-developed legs with which to lunge at their prey and long, sickle-shaped jaws they use to puncture them and inject a paralyzing venom. They grow from less than 0.04 inch to between 0.2 and 0.3 inches (from <1 mm to 6-8 mm), thriving on several species of aphids as well as on thrips, whiteflies and spider mites — especially red mites. They will journey up to 100 feet in search of food and can destroy as many well received," Tillman said, adding that she fielded many questions from growers, some calling later for more information on adopting cover crops into integrated pest management systems for cotton.

Schomberg cautions that the system requires careful management. In the fall, they seeded alternating strips of cereal rye and legume cover crops. In the spring, they killed the 15-inch-wide strips of rye with an herbicide and followed by planting cotton in the same rows, using conservation tillage. "Spacing is key," he said. "You have to think about and tinker with your planting equipment." Killing cover crops, he added, is easier than killing a diverse population of winter weeds.

Glynn Tillman IJSDA ARS

Glynn Tillman IJSDA ARS

Georgia researchers planted cotton into rows of legume cover crop mixes to attract insect predators to prey on damaging worms.

as 200 aphids or other prey per week. They also suck down the eggs of leafhoppers, moths and leafminers and reportedly attack small caterpillars, beetle larvae and the tobacco budworm.

Minute pirate bugs (Orius spp.). These often-underestimated "true bugs" are very small — a little over 0.1 inch (3 mm) long. The adults' white-patched wings extend beyond the tips of their black, somewhat oval bodies. The briskly moving nymphs are wingless, teardrop-shaped and yellow-orange to brown.

Minute pirate bugs are common on pasture, in orchards and on many agricultural crops, including cotton, peanuts, alfalfa, strawberries, peas, corn and potatoes. They feed greedily on thrips, insect eggs, aphids and small caterpillars and can devour 30 or more spider mites a day. Clasping their assorted small prey with their front legs, they repeatedly insert their needle-like beaks until they have drained their victims dry. They are prodigious consumers of corn earworm eggs in corn silks and also attack corn leaf aphids, potato aphids, potato leafhopper nymphs and European corn borers. Minute pirate bugs can even deliver harmless but temporarily irritating bites to humans.

Because they depend on pollen and plant juices to tide them over when their preferred prey are scarce, minute pirate bugs are most prevalent near spring- and summer-flowering shrubs and weeds.

Big-eyed bugs (Geocoris spp.). Named for their characteristically large, bulging eyes, big-eyed bugs are key and frequent predators in cotton and many other U.S. crops, including warm-season vegetables. Geocoris punc-tipes and G. pallens are the most common of the roughly 19 Geocoris species found in North America.

Adult big-eyed bugs — normally yellow or brown but sometimes black — are oval and small (0.12 to 0.16 inch, or 3-4 mm, long). Their unusually broad heads are equipped with piercing, sucking mouthparts. The similarly armed nymphs look like smaller, grayer versions of the adults.

Big-eyed bugs are omnivorous. Their diet includes plants but they prefer to prey on smaller insect and mite pests. They have been observed charging their intended victims, stabbing them quickly with their extended beaks and sometimes lifting them off the ground in the process.

Big-eyed bugs attack the eggs and small larvae of bollworm, pink boll-worm and tobacco budworm and most other lepidopteran pests. They also target all life stages of whiteflies, mites and aphids and the eggs and nymphs of plant bugs. Laboratory studies indicate that a ravenous, growing nymph can exterminate 1,600 spider mites or about 250 soybean looper eggs before reaching maturity; adults have bolted down 80 spider mites or four lygus bug eggs a day.

Syrphid flies. Also known as hover flies because they hover and dart in flight, these brightly colored bee and wasp mimics are unusually voracious predators, as larvae, of aphids and other slow-moving, soft-bodied insects.

Depending on the species, many syrphid flies over-winter, giving rise to adults in spring. Adult syrphid flies feed on pollen, nectar and aphid honeydew. Each female lays hundreds of white, football-shaped eggs, about 0.04 inch (1 mm) long, amidst aphid colonies. The narrow, tapered slug-like larvae that hatch from these eggs can pierce and drain up to 400 aphids apiece during the two to three weeks it takes them to complete development. Unable to perceive their prey except through direct contact, syrphid fly larvae find their dinners by flinging their forward ends from side to side.

0 0

Post a comment