RELATING DEGREE-DAY ACCUMULATIONS TO CALENDAR DATES - ALFALFA WEEVIL (COLEOPTERA, CURCULIONIDAE) EGG HATCH IN THE NORTH CENTRAL UNITED-STATES

We present a technique for determining dates of alfalfa weevil, Hypcra postica (Gyllenhal), egg eclosion by correlating degree-day accumulat ions with calendar dates. This technique uses historical climate data from various locations to calculate the median date a degree-day accum ulation has been reached. ClimProb 3.1, a computer software program an d weather database, was used to assess these correlations. We used 165 locations in 12 midwestern states for the analysis. Sixty years (1931 -1990) of continuous daily climate data (maximum temperature, minimum temperature, and liquid precipitation) were used for each location. We began degree-day accumulations on 1 January of each year and used a m inimum developmental threshold of 8.9 degrees C (48 degrees F). Degree -day accumulations were determined using a sine-wave method. The relat ionship between the date when the accumulated degree-days reached a th reshold and the location (expressed as degrees north latitude) was qua dratic from 36 degrees N to 48 degrees N. The technique gives approxim ate dates when egg hatch is likely to occur throughout the north centr al United States, and these dales can be used to augment existing deci sion criteria for initiating sampling programs for alfalfa weevil. Thi s technique can be used for other pest management programs that depend on estimating pest development.