Variation between biotype E clones ofSchizaphis graminum(Homoptera: Aphididae)

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Abstract
Phenotypic and genotypic variation was investigated between biotype E clones of the greenbug,Schizaphis graminum(Rondani).S. graminumwas collected from wheat and sorghum fields in seven Kansas counties, USA. Colonies representing single maternal lineages (clones) were initiated and maintained in an insectary, and were verified as biotype E. An allozyme survey among clones did not detect any polymorphism at 24 enzymatic loci. We were unable to detect interclonal variation for nymphal survivorship, age at first reproduction, fecundity, and reproductive lifespan. Variation among genetically homogeneous daughters within clones was as great as variation among different clones for the above parameters, due to microenvironmental effects. However, by using the intergenic spacer in the rDNA cistron as a molecular fingerprinting tool, we identified 56 unique maternal lineages among 61 clones tested. The length of the intergenic spacer varied within individualS. graminum, and different maternal lineages had unique sets of spacer sizes. However,S. graminumwithin a single clone shared the same sets of spacer sizes. Extensive molecular genetic variation was found among biotype E clones, despite a lack of variation in additive genetic traits. Thus, biotype E populations are made up of many genetically distinct clones and do not represent an asexual proliferation of one or a few maternal lineages.