GEOGRAPHIC INCIDENCE AND DAMAGE LEVELS OF ALFALFA SEED CHALCID, BRUCHOPHAGUS-RODDI (HYMENOPTERA, EURYTOMIDAE), IN SASKATCHEWAN, AND ITS RELATIONSHIP TO WEATHER AND AGRONOMIC VARIABLES AND PRODUCTION PRACTICES

A 5-year survey of Saskatchewan alfalfa (Medicago sativa L. sensu late ) seed fields was undertaken to determine the level of infestation by the alfalfa seed chalcid, Bruchophagus roddi (Gussakovsky). Seed sampl es were taken from commercial seed fields, hay fields, and roadsides j ust before pod maturity. From sample lots of 250 pods, the numbers of healthy, chalcid-damaged, and frozen or immature seed were determined. Later, producers were questioned about the attributes of and manageme nt practices employed in their fields. Seed yields and infestation lev els were correlated with temperature, precipitation, and degree-day da ta from the year of and the year preceding seed collection. Alfalfa se ed chalcid infestation level was correlated most closely with the temp erature and rainfall in July and August of both years. The proportion of damaged seed was highest the year following warm, dry summers. Alfa lfa cultivar also influenced infestation levels; winter-hardy cultivar s that became dormant early in the autumn had lower levels of chalcid- damaged seeds than less hardy cultivars which maintained growth later in the season. Management practices such as the use of insecticides (f or plant bug and aphid control), fertilizers, and herbicides, size or age of field, soil type, and application of irrigation water did not a ffect the proportion of seeds injured by chalcids.