Production of stable flies (Stomoxys calcitrans) from straw bedding packs and sawdust compost barns, two alternative cold winter housing systems for dairy cows

Stable flies, Stomoxys calcitrans (L.), are pests of dairy cows and other large livestock, developing as maggots in soiled bedding and other decaying organic material. We asked how debris from two different winter housing systems, outdoor straw bedding packs and covered sawdust compost barns, might compare as habitat for stable flies the following summer. Compared to compost bedding, we expected straw pile debris to be a better substrate, resulting in more and larger flies.

In winters of 2013 and 2014, independently managed herds of 21-22 cows from the certified organic dairy herd at the University of Minnesota’s West Central Research and Outreach Center in Morris were housed from November to May in replicated winter housing systems. After transfer to summer pasture, emergence traps were placed on debris piles to quantify stable fly emergence and fly size. Alsynite® sticky traps were placed adjacent to the piles to measure fly abundance, and flies were measured and dissected to assess size and female gonotrophic age. During peak emergence of both years, traps indicated straw piles produced significantly more flies (46-fold more in 2013) than compost piles (p < 2.2e-16). Adults from both sources were equal in size. Nearby sticky traps showed adults were equally abundant around both types of piles, and 57% of females captured at both types of piles were previtellogenic, indicating they emerged locally. Our results show that compost packs may help control fly numbers in summer, and straw piles present a serious fly production liability if not disposed of properly.