GENERATION OF CLONAL DIVERSITY BY SEXUAL REPRODUCTION IN THE GREENBUG, SCHIZAPHIS-GRAMINUM

In the United States, the greenbug, Schizaphis graminum (Rondani), rep roduces primarily by apomictic parthenogenesis. Although a periodic se xual cycle exists, the extent to which it occurs naturally and its inf luence on the genetic variability of greenbug populations is unclear. Length variation in the intergenic spacer (IGS) of the rRNA cistron in the greenbug indicates that populations are made up of many genetical ly distinct clones. Previous laboratory studies have shown the stabili ty of the IGS within parthenogenetic clones, By inducing the sexual re productive cycle of the greenbug, we conducted both intra-and inter-cl one matings and studied the inheritance of the IGS in the offspring. I n both mating schemes, rearrangements in the IGS were apparent. IGS di versity found among the offspring could be attributed to unequal cross -over and probably other molecular drive events during meiosis. Period ic sexual reproduction is a primary mechanism for the generation and m aintenance of genetic variability in greenbug populations, and explain s the level of clonal diversity found in previous studies.