Abundance of the rose-grain aphid, metopolophium dirhodum, on barley in canterbury, new zealand, 1984-87

Abstract

Spring populations of Metopolophium dirhodum (Walker) (Hemiptera: Aphididae) on barley, at Lincoln and elsewhere in Canterbury, New Zealand, declined markedly during 1984-87. Spring suction-trap catches of M. dirhodum also declined at the same time. Numbers of immigrant M. dirhodum on young barley, and maximum aphid population density on the crop, were positively correlated with suction-trap catches of M. dirhodum during the preceding week or month, respectively. Egg numbers of the most abundant predator, Micromus tasmaniae Walker (Neuroptera: Hemerobiidae), and mummy numbers of the parasitoid, Aphidius rhopalosiphi De Stefani-Perez (Hymenoptera: Aphidiidae), increased relative to aphid numbers during the study. Entomophagous fungus-disease incidence could not be related to monthly rainfall, and the decline in aphid numbers during die study period was apparendy not related to disease incidence. It is suggested that aphid population regulation by predators and parasitoids in the wider habitat of M. dirhodum could reduce the rate of immigration, and hence aphid populauon growth, in a given crop. © 1988 Crown.