University of Nebraska-Lincoln Extension, Institute of Agriculture and Natural Resources

July 7, 2006

Cowpea aphids found feeding in Dixon County

Cowpea aphids, Aphis craccivora, were found in alfalfa a couple weeks ago in Dixon County. The grower cut the alfalfa and we haven’t received further reports of this insect, but in a dry year cowpea aphids can become a problem. This insect was first reported in Nebraska in Knox County in 1999. In late July 2002 economic levels occurred in some fields in northeast Nebraska. Since many growers were in the process or close to harvesting the third cutting, most chose to take the cutting and watch the regrowth. Some fields were treated in 2002.

Adult cowpea aphid is shiny black while nymphs are gray.
(Photo by Jack Kelly Clark, Statewide IPM Project, ©2000, University of California)
The cowpea aphid is easily distinguished from other aphids in alfalfa since it is the only black aphid likely to infest the crop. In general, it is a relatively small aphid, less than 2 mm long. An excellent color image of the cowpea aphid can be found on a University of California web site: http://www.ipm.ucdavis.edu/PMG/A/I-HO-ACRA-AD.004.html.

Non-winged and winged adults are usually shiny black, while the smaller nymphs may appear to be a dull gray to black. The first half of the antennae is white, and the legs are usually a creamy white with blackish tips. In alfalfa, these aphids prefer to feed on young terminal growth, but can be found infesting leaves, blooms, and stems. Damage symptoms include yellowing, wilting, and dieback. In general, legumes can be seriously damaged, either by direct insect feeding or by the transmission of virus diseases. This aphid produces a considerable amount of honeydew upon which sooty mold grows. The honeydew also makes the alfalfa sticky, which causes problems with harvest.

The cowpea aphid is generally distributed across North America and has been reported in at least 28 states and in three Canadian provinces. This aphid species also has an extensive host range with a marked preference for legumes. Other known host plants are apple, carrot, cotton, cowpea, dandelion, dock, goldenrod, kidney bean, lambsquarters, lettuce, lima bean, pinto bean, peanut, pepperweed, pigweed, red clover, shepherdspurse, vetch, wheat, white sweet clover, and yellow sweet clover. The aphid lives throughout the year without producing sexual forms and they are always parthenogenetic viviparous females (ready to produce live offspring at birth).

Insecicide tests at the Haskell Ag Lab showed good control with Mustang Max, Warrior, and Lorsban.

Keith Jarvi
Integrated Pest Management
Northeast REC, Norfolk

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Copyright 2006 by the University of Nebraska Board of Regents. All rights reserved.
Published by University of Nebraska-Lincoln Extension in the Institute of Agriculture and Natural Resources Cooperating with the counties and the U.S. Department of Agriculture.
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