Nuisance Flies of Cattle

Flies have been around since Bill Peach’s portly rambles through the outback (mid 1970’s for those with milk teeth) waving his hands and Akubra at the incessant irritation. Buffalo fly (Haematobia irritans exigua) is the major cause of “fly worry” in the tropical and pastoral zone cattle industry. Its impact and control are well described on industry websites (e.g., MLA, and Flyboss).

Attracting less attention are the “nuisance flies” of cattle. These include stable flies (Stomoxys calcitrans), bush flies (Musca ventustissima), house flies (Musca domestica) and March flies (Tabanid flies). Strike flies/blowflies (Calliphoridae) rarely cause huge problems in cattle, but any cattle with strike wounds, particularly in northern areas, should be investigated for the exotic pest screw-worm fly.

While we have all seen cattle bunched together stamping their feet, the impact of nuisance flies is, perhaps, underestimated. They are important for the following reasons:

1. They cause measurable production loss. For example, in American production systems Taylor and others estimated losses in pre-weaned calves, pasture finished calves and feedlot animals at 6, 26 and 9kg respectively (follow the link for the full article).
2. The nuisance flies are associated with disease transmission. Cattle producers are well versed in the role of flies in transmitting pinkeye. It’s also suspected that bunching from fly worry, particularly in feedlots, facilitates spread of respiratory pathogens.
3. The biting varieties (stable flies and march flies) are known spreaders of a range of exotic diseases e.g. Surra, (Trypanosoma evansi).

The life cycles of bush, stable and house flies are roughly similar (this link for details), insofar as they all lay eggs in decomposing manure and vegetation. Individual variation may give some leads for control: for example, stable flies have a strong preference for horse dung to lay eggs in. Cleaning up droppings from pen riders’ horses breaks the transmission cycle.

Patently, control effort is commensurate with the size of the problem and potential for production losses/animal welfare issues. Feedlots are at greatest risk of major impact, but other producers should be aware of the potential for fly worry in specific circumstances. These include yard weaned calves and cattle held in confinement for trucking.

Control in feedlots is well described in their RULES based approach . We will draw on some of these points in the following discussion:

Environmental control: This aims to break the reproductive cycle of the flies with good hygiene, and where possible limit access of flies to cattle. It includes, but is not limited to:

• Good feedlot design. Ensure proper siting (including for breeze), proper slopes on pens to reduce water pooling and waste disposal remote from the pens.
• Good pen and bunk sanitation, particularly with silage which is a good breeding medium.
• Isolate pens with existing diseases spread by flies (specifically, pinkeye).
• Using fly baits, traps (a lot of debate about their utility), and fly buzzers/fly paper in enclosed areas.
• Target areas preferred by different fly types (e.g., stable flies like vertical surfaces which may be treated with insecticides).
• Remove horse manure if horses are a feature of the operation. This will also benefit the horses!

Chemical Control is often needed in feedlots and sometimes other settings. While this discussion is limited to direct animal application there is a place for chemical use in the environment, discussed here and here.

Chemical use will be needed seasonally in many areas but only some seasons the further south you go. Wet, warm seasons may extend the fly season.

Nuisance flies can be attacked with at least 3 chemical groups (OPs, SPs and MLs), and 4 application methods (back rubber – individual application; pour on; jet/dip and ear tags). Some things to remember:

• Treat when fly numbers get to impact level. Do not treat as a routine. It is not always necessary

• Resistance to SPs and OPs is widespread. Always monitor duration of activity against label claims.
• In protracted seasons retreat with a different chemical group
• Check the WHP and ESI against your marketing plans. Also be aware that specific QA programs may have something to say about ectoparasiticides.

This search tool allows you to check what is available for the different application methods. Keep in mind that there may be side benefits to choosing a particular chemical (for example, MLs will help with worm and lice control), but always choose the best drug to fit the requirements (species of flies, expected duration of activity needed balanced against WHI/ESI and specific market requirements).

References:

David B Taylor, Roger D Moon Darrel R Mark, (2012): Economic Impact of Stable Flies (Diptera: Muscidae) on Dairy and Beef Cattle Production. Journal of Medical Entomology, Volume 49, Issue 1, 1 January 2012, Pages 198–209, https://doi.org/10.1603/ME10050.

Further Reading.

R Urech, PE Green, AG Skerman, MM Elson-Harris, JA Hogsette, RL Bright, GW Brown: Management of nuisance fly populations on cattle feedlots. MLA FLOT.306, 2004, particularly P22 onwards.