Bean and Cowpea Aphids
Bean aphid, Aphis fabae Scopoli; Cowpea aphid, Aphis craccivora Koch, Aphididae, HEMIPTERA
Adult - These soft-bodied, pear-shaped insects have antennae which are shorter than their bodies and a pair of cornicles (tailpipe-like appendages). They may be winged or wingless but the wingless forms are most common. The bean aphid has a dark green to black body between 2 and 2.6 mm long with white appendages. The cowpea aphid has a shiny black body with white appendages and ranges from 1.5 to 2.5 mm long.
Egg - The egg stage probably does not occur in North Carolina.
Nymph - Though smaller than adults, nymphs resemble the wingless forms in shape. Bean aphid nymphs are green, the last instar having five to seven pairs of white spots on the back of its abdomen. Cowpea aphid nymphs are pale green to gray with a powdery coating.
Distribution - Bean and cowpea aphids occur in many temperate and subtropical regions of the world. In North America, the bean aphid can be found from New Brunswick to Florida and westward to California. The cowpea aphid has been reported in at least 28 scattered states and in three Canadian provinces.
Host Plants - A general feeder, the bean aphid infests a large number of fruit, vegetable, agronomic, and ornamental plants as well as many weeds. A few of its vegetable hosts include asparagus, broad and lima beans, carrot, celery, corn, cowpea, cucumber, eggplant, lettuce, onion, pea, pepper, potato, spinach, tomato, and turnip. In states where winters are more severe than here in North Carolina, the euonymus shrub serves as the primary winter host plant. In many southern states, weeds such as dock, lambsquarters, and shepherdspurse are favored summer hosts.
Host plants of the cowpea aphid include alfalfa, apple, carrot, cotton, cowpea, dandelion, dock, goldenrod, kidney bean, lambsquarters, lettuce, liima bean, pinto bean, peanut, pepperweed, pigweed, red clover, shepherdspurse, vetch, wheat, white sweet clover and yellow sweet clover.
Damage - Congregating on lower leaf surfaces and on terminal buds, aphids extract plant sap. Leaves curl and pucker and seedling plants may become stunted and die. On lima bean, bean aphids attack terminal leaves, flower heads, and stems of pods. Infested plants develop yellow foliage, may become dwarfed and malformed, and lose vigor. A dark sooty mold often grows on the honeydew-coated surfaces of aphid-infested plants.
Feeding and reproduction increase with warm weather in spring. Wingless female adults, known as "stem mothers," give birth to about 80 nymphs over a 2-1/2 week period. At temperatures of about 11.5 C (53 F), nymphs develop into adults in about 22 days. At warmer temperatures of about 28.5 C (83 F), development takes only 5 days. Most nymphs mature into wingless females, but periodically, winged females develop and migrate to new host plants. These adults produce offspring like theie wingless counterparts and thereby colonize new plants. Reproduction continues throughout the winter at a reduced rate and many generations are produced each year. Cowpea aphids have a similar life history though rates of development may vary.
Lady beetles and their larvae, lacewing larvae, syrphid fly larvae, and stilt bugs all feed on aphids. During periods of high humidity, fungus diseases also reduce populations.
For up-to-date chemical recommendations, consult the current North Carolina Agricultural Chemicals Manual
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