Aphids of the genus sitobion occurring on grasses in Southern Australia

Three forms of Sitobion Mordvilko occur commonly on grasses in southern Australia. S. nr fragariae (Walker), collected in Tasmania, Victoria, New South Wales, South Australia and Western Australia, has a diploid chromosome number of 18, and differs in electrophoretic mobility of enzymes at several loci from S. miscanthi (Takahashi), also with 2n = 18. A third form is here regarded as being derived from S. miscanthi, but differs from it in enzyme mobility at 2 loci and has 2n = 17, apparently resulting from an autosomal fusion. A fourth form, with 2n = 20, has been collected in the Sydney region on 2 occasions. It is electrophoretically identical to the 2n = 17 form. The 2n = 17 and 2n = 20 forms are concluded to be chromosomal races of S. miscanthi. The seasonal distribution of all forms is recorded; S. nr fragariae is common in spring, S. miscanthi (2n = 18) has been collected only in November‐December, and S. miscanthi (2n = 17,20) in November‐December and March‐July. This suggests different environmental tolerances for the 3 major forms.