Aphids
Cotton aphid, Aphis gossypii Glover
Cowpea aphid, Aphis craccivora (Koch)
Aphididae, HEMIPTERA


DESCRIPTION

Adult - Several species of aphids attack cotton but the cotton aphid and the cowpea aphid are most common. Adult aphids are about 2 mm long and may be winged or wingless. The cotton aphid is pale to dark green in cool seasons and yellow in hot, dry summers. The adult cowpea aphid is shiny black with white appendages.

Nymph - Cotton aphid nymphs are smaller than but similar in shape and color to the wingless adults. Cowpea aphid nymphs are pale green to gray with a powdery coating.


BIOLOGY

Distribution - Generally distributed throughout temperate, subtropic, and tropic zones, the cotton aphid occurs in all cotton-producing areas of North Carolina. The cowpea aphid has been reported in at least 28 scattered states and in three Canadian provinces.

Host plants - The cotton aphid infests cotton, okra, hibiscus, cowpea, citrus, cucurbits, strawberry, bean, spinach, tomato, clover, asparagus, catalpa, violet, hydrangea, begonia, ground ivy, gardenia, and several weeds. Host plants of the cowpea aphid include alfalfa, apple, carrot, cotton, cowpea, dandelion, dock, goldenrod, kidney bean, lambsquarters, lettuce, lima bean, pinto bean, peanut, pepperweed, pigweed, red clover, shepherds purse, vetch, wheat, white sweet clover, and yellow sweet clover.

Damage - In spite of the fact that many aphids infest cotton, these insects are only secondary pests. Congregating on lower leaf surfaces and on terminal buds, aphids extract plant sap. If weather is cool during the spring, populations of natural enemies will be slow in building up and heavy infestations of aphids may result. When this occurs, leaves begin to curl and pucker; seedling plants become stunted and may die. Most aphid damage is of this type. If honeydew resulting from late season aphid infestations falls onto open cotton, it can act as a growing medium for sooty mold. Cotton stained by this black fungus is reduced in quality and brings a low price for the grower.

Life history - Little information is available on the biology of the cowpea aphid although the life history of the cotton aphid is well known. Cotton aphids overwinter as adults in the cotton belt, and as eggs in cooler climates. In the cotton belt, winged adults hibernate in soil or field debris. During warm periods, they fly to weedy hosts, and continue their life cycle until cool weather forces them back into hibernation. In spring, winged females fly to suitable host plants and give birth to living young. In the cotton belt, all progeny generally develop into wingless females. Whenever crowding occurs or food becomes scarce, winged adults develop and fly to new host plants. Male and female adults occur in northern states.

Females produce an average of 84 nymphs. Under favorable conditions, a nymph will mature within 4 or 5 days and begin producing its own progeny. In the South, reproduction may continue all winter so that as many as 57 generations may be produced each year.


CONTROL

Aphid populations on cotton are generally of no economic concern in North Carolina due to naturally occurring controls and insecticides directed at other cotton pests. Should early or late season populations build up, consult the current North Carolina Agricultural Chemicals Manual.