May 23, 2008

Pink form of the pea aphid, Acyrthosiphon pisum, found this week for the first time in Nebraska, in alfalfa fields near David City. While this photo shows a neon pink aphid, in natural light the insect appears to be a more subtle pink/beige in color.

A number of unusual aphids were found this week in alfalfa fields near David City. These aphids were not green, but were more of a beige/pink color. They are thought to be the pink form of the pea aphid, Acyrthosiphon pisum. This is noteworthy because UNL entomologists have not previously found the pink form of the pea aphid in Nebraska, field scouts may not be aware of this aphid form, and some biological differences exist between pea aphids forms.

The vast majority (90-95%) of the pea aphids collected from the Butler County field were typical green pea aphids. The pink insect is harder to see in a sweep net and could be overlooked at first, as the color often is more of a beige/pink mix rather than a "hot pink" that would be more visible in a sweep net. Although the pea aphid pink form has existed in Europe for some time, it wasn't noted in the U.S. until 1979 when it was found in New York. Since then it has been found in Ohio, Michigan, Utah, California, and Missouri, and probably is present in many other states.

The pink pea aphid form was often the dominant form found in Calfornia in spring collections; the green form is more typical of summer collections. The reason for this is unclear, but could be related to temperature effects on aphid reproduction and/or different biological control species (predators) as temperatures increase.

Some research found that parasitic wasps prefer to attack the green forms more than the pink forms of pea aphids. Research on the European red/pink biotype of pea aphid indicates that it easily overcame pea aphid resistance in a number of U.S. alfalfa cultivars. These observations indicate continued need for Nebraska alfalfa crops to be monitored.

Michael Rethwisch
Extension Educator in Butler County