SEASONAL ABUNDANCE OF 3 LYGUS SPECIES (HETEROPTERA, MIRIDAE) IN OILSEED RAPE AND ALFALFA IN ALBERTA

Populations of lygus bugs were sampled from 1982 to 1986 in fields of oilseed rape, Brassica campestris L. and B. napus L., and alfalfa, Medicago sativa L., in Alberta. Of the three species collected, Lygus elisus Van Duzee was the most abundant in oilseed rape in 4 yr, and L. lineolaris (Palisot de Beauvois) was the most abundant in the 5th yr. L. borealis (Kelton) was the most abundant in alfalfa. All three species reproduced and reached maturity in oilseed rape and alfalfa. Lygus adults were first collected from oilseed rape when it reached the bud stage. Populations reached a peak in August when oilseed rape was in the early pod stage. A single generation of lygus was completed in the three crop species. Seeding date influenced the abundance of lygus in oilseed rape such that the highest densities were found in the crops that reached the bud stage earliest. Lygus bugs are potentially serious pests of oilseed rape because their phenology ensures that later-instar nymphs and adults are present in the crop when seeds are developing.