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Title: BIOTYPIC DIVERSITY IN GREENBUG (HEMIPTERA: APHIDIDAE): CHARACTERIZING NEW VIRULENCE AND HOST ASSOCIATIONS

Author
item Burd, John
item Porter, David

Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/19/2005
Publication Date: 6/30/2006
Citation: Burd, J.D., Porter, D.R. 2006. Biotypic diversity in greenbug (Hemiptera: Aphididae): characterizing new virulence and host associations. Journal of Economic Entomology. 99(3):959-965.

Interpretive Summary: Biotypic variation among populations of the greenbug has been a driving force behind wheat, barley, and sorghum breeding programs since the designation of the first biotype by Wood in 1961. In the present study we assessed the composition of greenbug biotypes on wheat, sorghum, and noncultivated grasses over a large area and found that overall biotypic diversity was much greater among greenbugs collected from noncultivated grasses, which would be expected if indeed greenbugs diverged on grasses. The most virulent biotypes were not present on wheat or sorghum, but were collected from noncultivated grass hosts, thus providing further evidence that cultivated crops play a limited role in exerting selective pressure for biotype development. Overall, our findings support the contention that the greenbug species-complex is composed of host-adapted races that have diverged on noncultivated grasses and greenbug biotypes that occur on cultivated wheat and sorghum are merely small subsets of the host-adapted races. Plant resistance to greenbugs will continue to be an important strategy in pest management; however, plant breeders will need to consider local host races, not just the predominant biotypes, when screening for resistant plants.

Technical Abstract: Biotypic diversity of the Greenbug, Schizaphis graminum (Rondani), was assessed among populations collected from cultivated wheat and sorghum and their associated noncultivated grass hosts. Greenbugs were collected during May through August 2002 from 30 counties within Texas, Oklahoma, Kansas, and Nebraska. Five of the eight documented greenbug biotypes were collected; however, biotypes C, F, and K were not detected. Biotypes E and I exhibited the greatest host range and, and were the only biotypes collected in all four states. Sixteen greenbug clones, collected from eight plant species, exhibited unique biotype profiles. Eleven were collected from noncultivated grasses, three from wheat, and two from sorghum. The most virulent biotypes were collected from grass hosts. The observed high degree of biotype diversity among noncultivated grasses supports the contention that the greenbug species-complex is composed of host-adapted races that diverged on grass species well before the advent of modern agriculture.