Degree-day requirements for alfalfa weevil (Coleoptera: Curculionidae) development in eastern Nebraska

The alfalfa weevil, Hypera postica (Gyllenhal), is a serious, yet sporadic defoliator of alfalfa, Medicago sativa L., in Nebraska. A 2-yr study was conducted in 2005 and 2006 to test for variation in degree-day requirements by location in eastern Nebraska. Sampling took place along a latitudinal gradient in three regions of eastern Nebraska. Three fields were sampled in each region during the 2 yr of the study. Alfalfa weevil larval degree-day requirements were found to vary by latitude in eastern Nebraska. Alfalfa weevil larvae were discovered in southern regions after fewer developmental degree-days had accumulated than in fields in the northern regions. Alfalfa weevils may be more damaging to alfalfa in southern regions than in northern regions of eastern Nebraska because they emerge earlier relative to alfalfa growth. Management implications of this shift in alfalfa weevil phenology are discussed.