Cotton Insects

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Arnet, J.D.; Bertrand, P.; Crawford, J.; Ellis, HC; Lambert, W.; McGlohon, N.; Suber, F.; Thompson, S.; Womack, H.; Brown, E.A.; Evans, B.R. Insect and Disease Identification Guide for IPM in the Southeast. The University of Georgia. Cooperative Extension Service Bulletin 849. September 1981. 59p.

Contents

Boll Weevil (Anthonomus grandis)

The adult boll weevil is small and hard-shelled, averaging about 1/4 inch (6 mm) in length, grayish or brown in color, becoming nearly black with age. It has a slender snout, half as long as the body. The close-fitting wing covers are smooth with fine parallel lines and are covered with short gray down or fuzz. The most characteristic feature about the boll weevil is the two spurs near the end of the front femur, the inner one being much longer than the other. There is a single tooth on the middle femur. The larva feeds inside the square. The mature larva is a white, legless, curved-bodied grub about 1/2 inch (13 mm) long and wrinkled with a brown head and mouthparts. As the larva begins to feed, the square will fall from the plant and the larva will continue to feed inside the square. It transforms into the pupal stage inside the hollowed-out cavity in which it has fed. The adult emerges and eats its way out of the square.

Two-Spotted Spider Mite (Tetranychus urticae)

Spider mites are not insects but very small arthropods closely related to insects. The adult mite is 8-legged and about 1/60 inch (0.4 mm) in length ranging from pale yellow to green, brown, or orange. Two dark spots show through the transparent body wall. The body is oval and sparsely covered with spines. Leaves of plants infested by spider mites present a peculiar appearance. Those lightly infested have pale blotches or spots showing through the leaf. In heavy infestations, the entire leaf appears light in color, dries up, and often turns reddish-brown in blotches or around the edge. The under-surface of lightly infested leaves will show silken threads spun across them. In heavy infestations, these threads may form a web over the entire plant, upon which the mites crawl and lay their eggs. The underside of leaves, on close examination, will be found covered with minute 8-legged mites which appear as moving dots on the leaves.

Bollworm Complex

Common Bollworm or Corn Earworm (Heliothis zea)
Tobacco Budworm (Heliothis virescens)

Eggs of both species are small (size of pin head) and hemispherical with ridges finning from the top down the sides. Color varies from white on the first day to tan with brown ring on the second day to gray with black spot on the third day. Larvae of both species are striped and very similar, with three pairs of thoracic legs, and four pairs of abdominal prolegs. Larvae grow to 1 1/2 inches in length (38 mm) and color varies from green to yellow to pink to brown.

Damage is caused by small worms feeding primarily on terminal growth and larger worms damaging squares, blooms and bolls. In heavy infestations, larvae may feed on stems and foliage. Bollworm feeding on bolls increases incidence of boll rot.

Cabbage Looper (Trichoplusia ni)

The larva has 2 pairs of abdominal prolegs, crawls with a distinct looping motion, tapers toward the head and is about 1 1/2 inches long (38 mm). There is a thin but conspicuous white line along each side of the body, and two others near the middle line of the back. The larva feeds on foliage for about three weeks and then forms a greenish pupa wrapped in white, tangled threads attached to the leaf of the plant.

Tarnished Plant Bug (Lygus lineolaris)

Adults are about 1/4 inch long (6 mm), somewhat flattened, oval in outline, and brown or bronze with yellow and red markings. The adults are winged and fly when disturbed. Eggs are inserted full length into the stems, petioles, or midribs of leaves. Eggs hatch and a small, yellowish-green nymph about 1/25 inch long (1 mm) appears. Nymphs are oval with long legs and antennae. They also have 4 rounded black dots on the thorax, and one on the base of the abdomen. The tarnished plant bug damages cotton by sucking plant juices from small pinhead squares. These squares later turn brown (blasted squares) and fall from the plant. The tarnished plant bug also feeds on the terminal of the plant where it may inject a toxin that causes the plant to form several terminals (crazy cotton) instead of the normal one terminal.

Bandedwinged Whitefly (Trialeurodes abutilonea)

Adults are about 1/16 inch in length (1.5 mm), very active, snow-white, and have 4 wings crossed by 2 indistinct gray lines. Nymphs are less than 1/13 inch in length (0.2 mm), immobile, pale-green in color and oval. They have fine, white, wavy threads radiating from their bodies. Both adults and nymphs feed on the undersides of the leaves, sucking out the plant juices. Whiteflies also excrete a glazed, sticky material (honeydew) on the leaves of the plant. This honeydew sometimes becomes covered with a sooty-colored fungus that can completely cover the foliage and lint.

Thrips (Frankliniella spp.)

Adult thrips may be yellow, brown, or black, depending on the species. They are slender, pointed at both ends, about 1/25 inch long (1 mm), and have 2 pairs of fringed wings. Nymphs are very similar to the adults, but paler in color, and are wingless. Eggs, nymphs, and adults, are found together throughout the summer. Thrips feed on the leaves and terminal buds by rasping the plant tissue and sucking out the juices. This feeding results in ragged, crinkled leaves that curl upward (possum eared). Heavy feeding on seedlings gives the plants a silvery appearance. In severe infestations, the terminal buds may be killed.

Fall Armyworm (Spadaptera frugiperda)

Female moths lay clusters of about 150 whitish eggs on both the top and undersides of leaves. Egg masses are covered with fine scales from the female moth. Larvae vary from tan or green to nearly black, have several stripes on the sides and/or the back which run the length of the body, and are about 1 1/2 inches long (38 mm). The fall armyworm will usually have an obvious inverted white "Y" on the front of the head capsule. The fall armyworm is only occasionally a pest of cotton. Since eggs are laid in masses, many small larvae may be found feeding on the undersides of cotton leaves. As the larvae grow, they disperse to adjacent plants and feed on squares, blooms and bolls.

Granulate Cutworm (Feltia subterranea)

Larvae in most cases remain below the surface of the ground, under clods, or other shelters during the day and feed at night. Larvae are robust and "greasy" looking, and about 1 1/4 inches long (31 mm). Cutworm damage is done when the larvae feed at night by cutting off cotton seedlings. Cutworms eat off the plants just above, at, or a short distance below the soil surface. Most of the plant is not consumed, merely being eaten enough to cause it to fall over. Damage often occurs in wet spots within a field or around field margins with a lot of vegetation.

Beet Armyworm (Spodoptera exigua)

Eggs are deposited on plant foliage in small, fuzzy masses. Larvae are pale green to blackish-green, about 1 1/4 inch long (31 mm), and have a black dot on each side of the thorax just above the second pair of thoracic legs. Larvae have four pair of abdominal prolegs. When first hatched, and until they are about 1/2 inch long (13 mm), they feed on the leaves in groups. Areas fed upon by small beet armyworms are usually speckled with black frass. Large larvae will feed on leaves, squares, blooms and bolls. Since eggs are laid in masses, infestations generally begin in small spots within a field and later spread.

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