Genetic-studies of rhopalosiphum in Australia

As part of a larger study of cereal aphids in Australia, we have examined samples of Rhopalosiphum Koch collected from grasses and cereals, using chromosomal and electrophoretic methods. The samples included Rhopalosiphum maidis (Fitch) with 2n = 8 and 2n = 9, R. padi (L.) with 2n = 8, R. insertum (Walker) with 2n = 10, R. rufiabdominalis (Sasaki) with 2n = 8, and a form similar to R. padi with 2n = 9. It was suggested on the basis of morphology and chromosomes that the latter form may be a hybrid between R. padi and R. insertum, but the electrophoretic patterns indicate that it is unlikely to be a hybrid and represents a separate introduction of a possibly undescribed species.