Plant bugs (Hemiptera: Miridae) on buckwheat and seed alfalfa crops in Manitoba : dynamics, yield implications and management

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Mostafa, Ayman Mahmoud
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The assemblages of plant bugs in buckwheat and seed alfalfa in southern Manitoba mainly include the tarnished plant bug, Lygus lineolaris (Palisot de Beauvois), and the alfalfa plant bug Adelphocoris spp. While the most abundant species of mirid plant bugs in buckwheat is L. lineolaris, this species and Adelphocoris spp. are about equally common in both organic and conventional fields of seed alfalfa. Lygus lineolaris has two generations in both crops in all the study locations. Lygus bug adults can move from drying swaths of canola near buckwheat and seed alfalfa late in the growing season. However, it seems that canola is not the only source of migrated lygus bugs late in the growing season. Low temperature and precipitation are likely to reduce the ability of migrating insects to move into the crops in late summer. Caged buckwheat experiments showed that buckwheat yields were reduced mainly as a result of feeding of L. lineolaris nymphs at flowering stage. Insecticidal manipulation of insect populations confirmed this finding, and indicated that the nymphal population was synchronized with the flowering stage of the plant, mainly during August. In field insecticide trials, control that reduced nymphal populations at the flowering stage provided yields 12 - 78% greater than in unprotected controls. Beauveria bassiana applied against adults in September produced a significant fungal infection in bugs, although the number of bugs in treated and control plots did not differ. The gain in yield as a result of this application was inconsistent. Similarly, conventional insecticide application in early September did not consistently provide significant yield benefits. Over three years, controlling the plant bug population in seed alfalfa crops late in August and Spetember did not result in greater yield quantity or quality than in untreated controls. This lack of yield response occured despite the insecticide application effectively controlling the plant bug populations.