Indigenous tribes of North America, Africa and Australia used fire for a variety of reasons including control of insects. Commercial livestock operators have typically not recognized the impact of fire in reducing parasites on animals. While the impact of fire on external parasites such as ticks has been documented, there has been little attention paid to how fire could be used to manage fly pests of cattle. Horn flies are an external parasite of cattle that cause over $1 billion in economic losses each year. Cattle serve as hosts for horn flies by providing blood meals and fecal pats that are used for laying eggs and overwintering pupa. Given the fire prone ecosystems of North America, range scientists and livestock entomologists are evaluating the response of horn flies (a non-native pest from Eurasia) to fires. The current trend in managing horn flies is with insecticides that are fed, sprayed or impregnated in ear tags. Resistance to chemical active ingredients is a major problem and is now widespread.
In 2011, cattle in Oklahoma and Iowa were evaluated for horn fly numbers. Cattle were either on pastures that were patch-burned (a portion of the pasture burned each year) or on pastures that had not been burned in over two years. All fires were conducted in March of that year. Horn flies were counted during periods of peak activity and data was evaluated for location and treatment effects. Cattle on pastures that were patch-burned had 41% fewer horn flies than cattle on pastures that had not been burned. The accepted economic threshold for treatment of horns flies is 200 flies per cow, with 300 flies per cow causing behavioral stress. The unburned pastures had >400 horn flies per cow, while the patch burn pasture cows had approximately half as many horn flies. It is thought that the application of fire is effective by two primary mechanisms: (1) cattle spend more time in the recently burned patch than unburned patches (as they are attracted to the highly palatable and nutritious plant regrowth after fire) and (2) fire in the dormant season (late winter and early spring) alters cow pats when pupa are overwintering in or below them.
Benefits of Fire Relative to Parasites
Using fire to manage horn flies is anticipated to have a number of positive impacts, including: (1) reducing horn fly numbers is expected to result in a reduction of stress annoyance behaviors such as twitching, head throwing and swishing of the tail and ultimately an increase in grazing time, (2) reducing horn flies has been documented in numerous studies to have a positive impact on cattle performance, (3) the potential impact of fire on any parasite of cattle is an exciting alternative to the use of pesticides and a potential strategy to avoid the development of resistance to chemical treatments, (4) fly pests of cattle have been documented to vector diseases (horn flies are suspected of transmitting anaplasmosis and face flies are suspected of transmitting pinkeye). Lastly, fire provides other benefits to pasture such as slowing woody plant encroachment and removing dormant plant litter and allowing for lush regrowth of grass.