Production of stable flies (Diptera: Muscidae) from two alternative winter housing systems for dairy cows

Stable flies, Stomoxys calcitrans (L.), are important biting pests of dairy cattle and other livestock. These flies develop in decaying organic matter, such as soiled animal bedding. As part of a larger study of management options in organic dairy, we asked how leftover debris from two winter housing systems, indoor sawdust compost barns and outdoor straw packs differ in numbers and size of stable flies produced the following summer.

This study was conducted at the University of Minnesota’s West Central Research and Outreach Center in Morris. In winter 2013 and 2014, independent herds of ~20 cows were housed from November to May in replicated housing systems. After transfer to summer pasture, we assembled fly traps at leftover piles (n=4): emergence traps to quantify stable fly emergence, and sticky traps to study ambient adults. Beginning 2014, we measured size of emerged flies and 30 ambient adult females. Sampled females were also dissected to determine gonotrophic age.

During peak emergence, straw piles produced significantly more stable flies than compost bedding (46x, 63x more in 2013 and 2014 respectively), but adults were equal in size. Sticky traps showed adults were equally abundant at both sources, indicating that either eggs were not laid in compost or maggots did not survive. 57% of females dissected were previtellogenic, indicating local emergence. These results show that compost is useful in managing stable fly numbers, while straw presents a serious stable fly production liability if not disposed of properly. The study is currently being repeated in 2015.