Resistance to synthetic pyrethroid pesticides is widespread and often at a high level in buffalo fly populations whereas resistance to organophosphate insecticides is less common and no resistance has yet been found to macrocyclic lactone compounds in Australian buffalo flies.
A short generation length coupled with a high reproductive rate makes buffalo flies particularly prone to the development of resistance. Insecticidal ear tags are particularly valuable tools in controlling flies because of the extended period of protection they offer (16 weeks from most products if resistance is not present). However, this makes these products more vulnerable to resistance development.
Some points to consider when designing a resistance management plan include:
These strategies are discussed in more detail below.
Where practicable delay until at least economic thresholds are met or cattle are starting to show clear fly worry. Sprays, dips and pour-ons give shorter periods of protection than tags, but when a different chemical group is used these methods can provide a valuable option at the beginning or end of the season to help reduce selection for resistance. Delaying the application of tags at the start of the season will give maximum protection from the tags during the high fly months and increase the possibility of getting good buffalo fly protection through to the end of the season without extra treatments.
The economic threshold for buffalo flies on beef cattle is 200 flies per animal or 30 per cow for dairy cattle. Waiting until flies reach this number, or until cattle are showing clear fly worry, is the most cost-effective approach and ensures that buffalo flies are not exposed to more chemical treatments than are necessary.
A three-year rotation incorporating synthetic pyrethroid, organophosphate and macrocyclic lactone tags is recommended. If a spray, pour-on or dip treatment is needed in the same year, use a different chemical group to that in the tags.
Rotate among chemical groups. It's not enough to simply change chemical brands.
Leaving tags in place after their effective protection period (usually 16 weeks) can expose buffalo flies to a sub-lethal concentration of chemical and increase selection for resistance.
Buffalo fly migration from neighbouring untreated herds can compromise resistance management programs. Coordinate buffalo fly treatments with neighbouring properties.
Consider using alternative or complementary methods for buffalo fly control to reduce chemical usage. For example, the use of buffalo fly traps or dung beetles can help to keep fly numbers below threshold levels reducing the number of chemical treatments required.
Strategically planning treatments for parasites such as tick, lice and worms, with regard to buffalo fly control programs, can provide effective resistance management and decrease labour costs. Read the product label to ensure the product isn’t unintentionally exposing non-target parasites to chemicals (e.g. products to treat buffalo fly may also affect ticks, worms or lice).