Occurrence of greenbug biotype K in the field

The success of managing greenbugs, Schizaphis graminum (Rondani), with plan t resistance has been challenged by the repeated occurrence of resistance-b reaking biotypes. Biotypes recognized as seriously damaging to sorghum, Sor ghum bicolor (L.) Moench, hybrids are C, E, I, and K. In 1995, biotype K, w hich damages sorghum resistant to biotype I, was first identified in a biot ype I greenbug colony being reared in the greenhouse. This colony originate d from greenbugs collected in a field of wheat in Haskell County, Kansas, i n April 1992, and was maintained on susceptible sorghum. Documenting the pr esence of biotype K in the field was imperative. Field samples of greenbugs collected from wheat and sorghum in Kansas and Oklahoma from 1996 to 1998 were identified to biotypes. These samples indicated that biotype I was the dominant biotype on both crops. Biotypes E and K were present in about 21 and 12% of the samples collected from sorghum in 1998, respectively. Biotyp e K was identified in samples collected from 11 counties in Kansas and 10 c ounties in Oklahoma during the sampling period. It is a potential threat to future sorghum hybrids that may rely on PI 550610 for protection against g reenbug damage. Studies conducted at constant temperatures of 22, 27, and 3 2 degreesC indicated that biotypes C, E, I, and K had similiar reproductive capacity and survival at 22 and 27 degreesC.