Ecology and control of the soybean aphid, Aphis glycines Matsumura (Homoptera: Aphididae)

The soybean aphid, Aphis glycines Matsumura (Homoptera: Aphididae) is an important pest affecting soybean. Populations cycle between a secondary summer host, where reproduction occurs by parthenogenesis and a primary host, where populations overwinter as eggs. In North America, primary hosts include R. cathartica L. (European buckthorn) and the native species, Rhamnus alnifolia L'Heritier and R. lanceolata Pursh the principal secondary host in North America is soybean, Glycine max (L.) Merr. The consequences of host alternation are of particular importance in the management of the soybean aphid. Firstly, population dynamics on both hosts may be at least partially interdependent. Host alternation may also affect the nature and extent of interactions occurring among the soybean aphid and its natural enemies on both hosts. This thesis explores aspects of the ecology and control of the soybean aphid on the secondary host, G. max and the primary host, R. cathartica. This research had the following objectives: (i) to examine overwintering dynamics of egg populations on R. cathartica, (ii) to describe the behaviour of a biological control agent, the parasitoid Aphidius colemani Viereck (Hymenoptera: Braconidae), with respect to host-plant preferences and a common coccinellid predator of the soybean aphid Harmonia axyridis Pallas, (iii) to assess the efficacy of two neonicotinoid insecticides, thiamethoxam and imidacloprid, for control of soybean aphid and (iv) to evaluate parasitism by A. colemani on soybean aphid populations reared on plants treated with neonicotinoid insecticides. The implications of this work for soybean aphid control in Ontario are discussed and recommendations for future research are made.