Seasonal abundance of stable flies and house flies (Diptera: Muscidae) in dairies in Alberta, Canada.

Seasonal abundance of stable flies and house flies was studied at four dairies in southern Alberta, Canada, from May to October in 1989, 1990, and 1991. Stable flies were active from May to October in all years and showed population peaks in August and September. The weekly rate of change of stable fly populations was influenced by temperature and accumulated degree-days above 10 degrees C. The weekly rate of change of stable fly populations showed four peaks which were attributed to the emergence of an initial generation which had overwintered, followed by an additional three generations. Stable fly attacks on dairy cows occurred mainly from July through October, corresponding with the last two generations. House fly population abundance was much lower than stable fly populations and showed peaks in June, July, and September. Weekly changes in house fly abundance were not influenced by temperature and only weakly influenced by accumulated degree-days above 10 degrees C. Peaks in the weekly rate of change were associated with emergence of an initial, overwintering generation followed by four generations produced throughout the summer.