INFLUENCE OF HIGH-TEMPERATURES ON THE SURVIVAL OF RHOPALOSIPHUM-PADI (L) (HEMIPTERA, APHIDIDAE) IN IRRIGATED PERENNIAL GRASS PASTURES IN SOUTH-AUSTRALIA

A field experiment in a perennial grass pasture showed that the surviv al of Rhopalosiphum padi (L.) (Hemiptera: Aphididae) was reduced when aphids were exposed to air temperatures of at least 36-degrees-C (32-d egrees-C at the base of the sward). The longevity, rate of reproductio n and fecundity of individuals also declined as the exposure temperatu re and duration of exposure increased. The results of the field experi ment were later corroborated by sampling an aphid population every 4-6 days over summer and regressing aphid numbers on daily maximum temper ature and duration of exposure to temperature. A model is proposed to estimate the numbers of aphids that survive in refuge areas over summe r in relation to temperature-induced mortality.