Sweep net sampling of canola (Brassica napus L.) was conducted in 2002 and 2003 to determine Lygus (Heteroptera: Miridae) species composition and parasitism levels in four regions of Montana. Regardless of region or seasonal change, Lygus elisus (Van Duzee) was the dominant species in all canola fields sampled, averaging 60–99% of the total adult populations. Lygus borealis (Kelton), Lygus keltoni (Schwartz) and Lygus lineolaris (Palisot) were detected at much lower levels. Total lygus population density was greatest in the southwest and central regions. The northeast and southwest regions had the greatest lygus species diversity. The proportion of L. elisus increased from early to late crop maturity stages in the southwest and central regions while there was no change in northeast and southwest canola production regions. Nymphal stages III–V were dissected to detect parasitism in 2003 only. Parasitism was found to be negligible in the dissection of 1,230 nymphs. Lygus population densities in canola indicate the potential for economic impact on Montana canola, especially in years when moisture is limited.
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