The bigeyed bugs, Geocoris spp., are generalist predators commonly found in a variety of crops and noncultivated plants nationwide. The common name refers to a characteristic feature of these insects, their rather large, protruding eyes. Bigeyed bugs are members of the family Lygaeidae (seed bugs), but belong to a subfamily containing only predaceous insects.
There are many different Geocoris species found throughout the U. S. The adults range in color from black and white to tan. The nymphs resemble miniature grayish adults. They are small (3-4 mm long) insects capable of feeding on a variety of types of prey such as insect eggs, aphids, mealybugs, spider mites, leafhoppers, bugs, and small caterpillars or beetle larvae. Each nymph may consume up to 1600 spider mites during its immature stages, and as many as 80 mites a day as an adult. Other laboratory studies have shown that each G. punctipes nymph consumes about 250 soybean looper eggs before it reaches the adult stage. In yet another lab study adult bigeyed bugs consumed up to four Lygus bug eggs per day. In laboratory and field studies they have been observed to feed on dead insects, although when given a choice they prefer live prey.
Geocoris also feed on plants; maximal survival and reproduction in the laboratory occurs when they have a mix of plant and insect food. In the laboratory they can survive for months on sunflower seeds and water. This plant feeding behavior is probably related to their evolution from seed feeding lygaeid bugs, and allows them to survive periods of low insect abundance. Their omnivorous feeding habits allow them to survive in a variety of habitats and contribute to biological control of pest species that become abundant. There is no evidence that their plant feeding causes significant injury to the plant. However, their plant feeding makes them susceptible to systemic insecticides; studies in cotton have shown reduced Geocoris survival on plants treated with systemic soil insecticides.
Bigeyed bugs have piercing sucking mouthparts. Field observations indicate that Geocoris usually attack prey simply by walking or running up to a potential prey, extending their beak and quickly inserting it into the prey. Geocoris may lift prey into the air, preventing the prey from attempting escape by running. They may drop to the ground if disturbed.
Like all true bugs, they go through incomplete metamorphosis. The immature nymphal stages resemble the adults, except they lack functional wings. Nymphal stages have similar behavior and feeding habits as adults, but tend to feed on smaller prey. Most bigeyed bugs go through five nymphal stages. Under laboratory conditions nymphal development takes about 30 days at 25°C and 60 days at 20°C. Although not well studied, it is reported that bigeyed bugs overwinter as adults or as eggs depending on the species and location.
Bigeyed bugs are particularly common in cotton, peanut, and soybean fields, and seem to prefer weedy areas in gardens. They are also common in managed turfgrass, such as home lawns.
Bigeyed bugs were effective predators of corn earworm eggs in cotton in experimental mass releases, but are not available for sale commercially. However, recent studies by USDA-ARS scientists have identified new artificial diets for bigeyed bugs based on ground beef and beef liver. This diet costs $2.50 per pound, compared with $300 a pound for rearing with insect eggs. Bigeyed bugs reared on the new diets produced more offspring, often mature faster and are up to 50% larger than field collected insects. Although not commercially available yet, these predators are important in natural control in many agricultural settings.
- Bob Wright, University of Nebraska
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