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The full complement of known greenbug, Schizaphis graminum (Rondani), biotypes found in the USA were subjected to a molecular phylogenetic analysis based on a 1.2-kb portion of the cytochrome oxidase I mitochondrial gene. In addition to these nine biotypes (B, C, E, F, G, H, I, J and K), a probable isolate of the enigmatic biotype A (NY), a 'new biotype' collected from Elymus canadensis (L.) (CWR), and an isolate from Germany (EUR) were included. Schizaphis rotundiventris (Signoret) was included as an outgroup. Genetic distances among S. graminum biotypes ranged from 0.08% to 6.17% difference in nucleotide substitutions. Neighbour-joining, maximum parsimony and maximum likelihood analyses all produced dendrograms revealing three clades within S. graminum. Clade 1 contained the 'agricultural' biotypes commonly found on sorghum and wheat (C, E, K, I, plus J) and there were few substitutions among these biotypes. Clade 2 contained F, G and NY, and Clade 3 contained B, CWR and EUR, all of which are rarely found on crops. The rarest biotype, H, fell outside the above clades and may represent another Schizaphis species. S. graminum biotypes are a mixture of genotypes belonging to three clades and may have diverged as host-adapted races on wild grasses.

The length of the intergenic spacer in the rRNA cistron varied within and among individuals of Schizaphis graminum (Rondani). Spacer lengths did not vary among offspring of a single maternal lineage (clone). The intergenic spacer was used as a molecular fingerprinting probe on individual aphids and to study spatial and temporal distributions of clones. A spatially nested sampling design was used in wheat and sorghum to estimate numbers of clones among aphids on leaves, among leaves on plants, among plants in fields, among fields in counties, among counties, and among dates. Each level of nesting added a level of clonal diversity to the entire population. 82.3% of the total population diversity was found among aphids on one sorghum leaf. Sampling additional leaves increased diversity slightly (5.4%), whereas plants (0.9%), fields (0.6% to 3.6%), and counties (1.2%) added very little. Sample dates contributed the highest increase in diversity (11%). Diversity rose and fell in wheat along with aphid numbers but remained constant in sorghum. Little variation in Mahalanobis distances could be explained by geographic distances. No genotypes were unique to any field, county, crop, or year. Kansas populations are made up of a large mixture of genetically diverse clones that recolonize wheat and sorghum each year. Sampling many plants, fields, or counties is an ineffective way to increase clonal diversity. Plant breeders developing crop resistance to S. graminum can expect plant entries to be exposed to most of the genetic diversity present in Kansas populations regardless of location.

We extend detection of arthropod predator gut contents by polymerase chain reaction (PCR), heretofore restricted to insect predators, to spiders. Single individuals of the corn lead aphid, Rhopalosiphum maidis, were detected in the guts of spiderlings of Oxyopes salticus up to 12 h after feeding; individuals of the congeneric bird cheiTy oat aphid, R. padi, were not detected. Unfed O. salticus and Misumenops sp. were also negative.

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