EVALUATING THE EFFECTS OF HARVESTING ALFALFA ON ALFALFA WEEVIL (COLEOPTERA: CURCULIONIDAE) AND PARASITE POPULATIONS IN MICHIGAN

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Abstract
The alfalfa weevil, Hypera postica (Gyllenhal), first found in Michigan in 1966, caused considerable damage to alfalfa throughout the state by 1971. In contrast to more southern regions, the alfalfa weevil lays very few eggs in the fall in Michigan. As a result, most eggs and larvae are present when the fields are ready for cutting in the spring.Different cutting dates were evaluated to determine the effects of cutting on populations of the alfalfa weevil, its primary parasite in Michigan, Bathyplectes curculionis (Thomson), and damage to the crop. Cutting at 507 degree-days (base 48°F (8.9 °C)) caused a 79% reduction in the number of alfalfa weevils produced and a 57% reduction of B. curculionis, while almost eliminating crop damage. Cutting at earlier and later times caused different reductions in populations of both insects and different crop damage.