In recent years, the cereal leaf beetle (CLB) Oulema melanopus (Coleoptera: Chrysomelidae), an important pest of wheat, barley, and oat throughout the world, has become a serious pest of cereal crops in Western Canada. Following CLB invasion, Tetrastichus julis (Hymenoptera: Eulophidae), the most efficient larval parasitoid of CLB, was introduced into the Canadian Prairies. I investigated the effect of landscape complexity, ranging from high (seminatural habitats > 50%) to low (semi-natural habitats < 30%) on the abundance of CLB and its parasitism in southern Alberta. Cereal leaf beetle abundance and the parasitism rate of T. julis responded positively to the proportion of CLB major hosts (wheat and barley) in the current and previous years at various spatial scales (0.5 to 2 km). Landscape diversity was negatively associated with CLB abundance. Cereal leaf beetle parasitism increased when there was a higher proportion of canola and alfalfa in the landscape. Cereal leaf beetle parasitism also positively responded to CLB abundance in cereal fields, indicating a density-dependent response. Overall, I concluded that diversification of crops and semi-natural habitats in the surrounding landscape are an important factor to reduce CLB numbers in the Canadian Prairies.Laboratory and field predation trials revealed for the first time the contribution of various predators to CLB control. Several species of Hippodamia (Coleoptera:iii Coccinellidae), carabids (Coleoptera: Carabidae) and nabid bugs (Hemiptera: Nabidae) were among the best predators of CLB immature stages under laboratory conditions, that also included Coccinella septempunctata (Coleoptera: Coccinellidae) and Staphylinidae. I found an average 24.5% of predation on sentinel eggs in wheat fields in 24 h trials. I developed a set of species-specific primers to detect CLB DNA in the gut content of generalist predators, which confirmed that Nabis americoferus and several Hippodamia species are the most promising predators of CLB in wheat. Nabis americoferus was the most abundant predator in the Lethbridge area and had 0.35 proportion positives for CLB DNA. Altogether, the predation studies highlight the importance of predators in CLB control, which has been neglected to date but can have important roles in sustainable pest management programs for CLB in cereal crops.

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