APHID POPULATIONS AND THEIR DAMAGE TO OATS IN BRITISH COLUMBIA

Abstract

Populations of aphids on Victory oats were studied during the 4 years 1957–60 at Vancouver, British Columbia. The aphids found, in order of abundance, were: the English grain aphid, Macrosiphum avenae (F.) (= granarium (Kirby)), the rose grass aphid, Metopolophium dirhodum (Walker), and the bird-cherry oat aphid, Rhopalosiphum padi (L.). M. avenae and R. padi overwintered as viviparae on small grains and grasses; M. dirhodum overwintered as eggs on Rosa spp. Winged migrants moved to spring-sown oats late in May or in June. Maximum aphid density was low in 1958, moderate in 1957 and 1959, and high in 1960. Predators and parasites were important factors in governing the aphid populations.Yield data from 25 pairs of insecticide-treated and untreated plots showed no significant advantage in yield of oats and only small gains in yield of straw from controlling aphids. The economic injury level for aphids on oats under conditions similar to those in the experimental fields is, therefore, higher than 47 aphids per tiller. General application of non-selective insecticides to control aphids on oats in British Columbia is not recommended.