Aphids of the genus Sitobion occurring on grasses in southern Australia.
The relationships between populations of Sitobion spp. feeding on grasses in southern Australia were investigated using allozyme electrophoresis. A species of this genus near S. fragariae, collected in Tasmania, Victoria, New South Wales, South Australia and Western Australia, had a diploid chromosome number of 18 and differed in electrophoretic mobility of enzymes at several loci from S. miscanthi (also 2n=18). A 3rd form was regarded as being derived from S. miscanthi, but differed from it in enzyme mobility at 2 loci and a diploid number of 17, apparently resulting from an autosomal fusion. A 4th form, with 2n=20, was collected in the Sydney region on 2 occasions. It was electrophoretically identical to the 2n=17 form. The 2n=17 and 2n=20 forms are concluded to be chromosomal races of S. miscanthi. S. fragariae was common in spring, S. miscanthi (2n=18) was collected only during November-December and S. miscanthi (2n=17 or 20) was collected in November-December and March-July. It is suggested that the 3 major forms have different environmental tolerances.