THE ROLE OF ANNUAL GRASSES IN THE PHENOLOGY OF RHOPALOSIPHUM-PADI IN THE LOW RAINFALL BELT OF SOUTH-AUSTRALIA

Rhopalosiphum padi (L.) (Hemiptera: Aphididae) was the first species of cereal aphids to colonise annual grasses across the state each year. Numbers were higher in the Lower Murray Valley than in the Mount Lofty Ranges or Adelaide Plains. At all locations, numbers generally increased until grasses reached the boot stage after which they declined. Alatoid production commenced in late July in response to crowding, but thereafter plant age and photoperiod were more important determinants. Metopolophium dirhodum (Walker) (Hempitera: Aphididae) and Sitobion nr fragariae (Hemiptera: Aphididae) first appeared in annual grasses in late July.