Biotypic Status of Six Greenbug (Homoptera: Aphididae) Isolates

Abstract

Seventeen entries from 10 crop species including sorghums, small grain cereals, and grasses were evaluated as seedlings to determine or confirm the biotypic status of six isolates of greenbugs, Schizaphts graminum (Rondani). Eight plant entries were rated for damage 20 days postinfestation with 10 first-instar greenbugs, and 13 entries were studied for antibiosis effects on number of days to reproductive maturity, fecundity, and longevity. Four greenbug isolates showed strong biotypic differences. These included biotypes B, C, E, and the Ohio isolate, herewith designated biotype F. Biotype F is nearest to biotype A in terms of plant response, but it differs in its ability to kill ‘Amigo’ wheat, Triticum aestivum L., and in morphology, having no dorsal stripe. Biotype F was also able to kill ‘Reubens’ Canada bluegrass, Poa compressa L., which was highly resistant to the other greenbug isolates tested. The Maryland isolate seemed to be nearest to biotype C in terms of biological and host plant responses although similarities to biotype E also existed. Greatest differences of the Oklahoma isolate included increased longevity on various plants and a higher virulence on ‘Kentucky 31’ tall fescue, Festuca arundinacea Schreb.