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

Author
item Shufran, Kevin
item PETERS, D - OKLA ST UNIV/ENTOMOLOGY
item Webster, James

Submitted to: Insect Molecular Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/27/1997
Publication Date: N/A
Citation: N/A

Interpretive Summary: The greenbug is a unique insect pest of wheat and sorghum because it reproduces asexually. Males are not present, and populations of greenbugs are made up of a mixture of genetically identical female clones. Despite this form of reproduction, greenbugs display an amazing amount of genetic diversity and are able to quickly adapt and damage resistant crop plants. Understanding how greenbugs are able to generate genetic diversity, allowing them to injure resistant crops, is an important step in developing management strategies that will be sustainable and environmentally friendly. Our study showed that greenbugs can generate genetic diversity by undergoing periodic sexual reproduction, whereby males are produced which then mate with females. Eggs are laid which result in offspring genetically unique from the parents and other offspring. Our research showed that only a small proportion of greenbugs in the field would have to reproduce sexually to generate the amount of genetic diversity necessary for them to adapt to resistant crop plants. This study provides important basic information that needs to be considered by the insect pest management industry.

Technical Abstract: Length variations in the intergenic spacer of the rRNA cistron in the greenbug, Schizaphis graminum (Rondani), have indicated that populations are made up of many genetically distinct clones. However, it has been difficult to explain this diversity because of the stability of the IGS within parthenogenetic clones. By inducing the sexual reproductive cycle (holocycle) 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, as well as the creation of new size variants. IGS diversity found among the offspring could not be attributed to meiosis alone, but also involved unequal cross- over and probably other molecular drive events. 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.