The impact ofAphidius rhopalosiphi(Hymenoptera: Aphidiidae) on populations of the rose grain aphid (Metopolophium dirhodum) (Hemiptera: Aphididae) on cereals in Canterbury, New Zealand

Abstract

The parasitoidAphidius rhopalosiphiDe Stefani-Perez was imported into New Zealand as a biological control agent against the rose-grain aphid (Metopolophium dirhodum(Walker)) in 1985. In 1988–89, the rate of parasitism byA. rhopalosiphiwas studied by rearing fourth instarM. dirhodumcollected from barley at Lincoln and other sites in Canterbury. The rate of parasitism at the time of peak aphid numbers at Lincoln was approximately 50% in winter barley and 100% in spring barley. In spring barley, peak numbers did not exceed five aphids per tiller, and regulation of aphid population density below this level was attributed to parasitism following a large immigration of adultA. rhopalosiphi.Suction trap catches ofA. rhopalosiphiincreased between 1984, prior to release, and 1989, while catches ofM. dirhodumshowed a corresponding decline.