Generation of clonal diversity by sexual reproduction in the greenbug, Schizaphis graminum.

In the United States, the greenbug, Schizaphis graminum (Rondani), reproduces primarily by apomictic parthenogenesis. Although a periodic sexual cycle exists, the extent to which it occurs naturally and its influence 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 genetically distinct clones. Previous laboratory studies have shown the stability of the IGS within parthenogenetic clones. By inducing the sexual reproductive cycle of the greenbug, we conducted both Intra- and inter-clone matings and studied the inheritance of the IGS in the offspring. In both mating schemes, rearrangements in the IGS were apparent. IGS diversity found among the offspring could be attributed to unequal cross-over and probably other molecular drive events during meiosis. Periodic sexual reproduction is a primary mechanism for the generation and maintenance of genetic variability in greenbug populations, and explains the level of clonal diversity found in previous studies.