Applying a pour-on insecticide early in the spring will reduce horn fly numbers by 75 percent, says a livestock entomologist from Agriculture Canada’s research centre in Lethbridge, Alta.
Combined with a two-week delay in grazing, it could reduce fly numbers by 95 percent.
“These results suggest that integrated approaches for combining range management and insecticide application may be the most effective means of achieving longer-term horn fly control,” Tim Lysyk said.
Horn flies and wood ticks are significant pests for range cattle, but studies at the Lethbridge research centre may give producers alternatives to insecticides amid mounting concerns about environmental effects, insect resistance and future availability of chemicals.
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At the Western Range Science Seminar held recently in Lethbridge, Lysyk outlined recent research in chemical-free control of the horn fly and the Rocky Mountain wood tick, two costly parasites for range cattle.
The painful bites of the horn fly affect cattle performance and weight gains. Tick infestations on animals can lead to paralysis. In severe cases in British Columbia, ranchers have lost large numbers of animals to tick paralysis.
The horn fly can be a significant concern for the livestock manager.
“If you think of a mosquito as having a fencing rapier, think of the horn fly as having a claymore,” Lysyk said.
Fly infestations of 10 to 250 per animal can result in significant weight gain reductions. Bites cause large lesions, especially when flies congregate in one place on the skin. Horn fly control now focuses on using insecticides on adult flies, either through pour-ons, self-application with oilers and dusters, or ear tags.
Direct application methods lose effectiveness within two weeks, and some fly populations have become resistant to cattle ear tags. These issues and increasing public concern about insecticides have prompted scientists to look for other control methods.
The answer might lie in a combination of grazing management and insecticide use. The horn fly overwinters in manure pats in a state of arrested development at the pupal stage.
Lysyk said this part of the fly’s life cycle may be a good target for control strategies.
Spring emergence may be another control opportunity. Computer models simulating emergence have been coupled with models showing the survival of flies in the absence of cattle. Results suggest that a four-week delay in spring grazing could reduce fly populations by 95 percent. However, such a delay is not economically feasible.
That is why Lysyk recommends a two week delay along with insecticide use as an alternative.
The biggest challenge in wood tick control may be that registration for Lindane, the popular tick control pesticide, expires this year.
“Without Lindane, ranchers in the interior of B.C. will have no method to prevent tick paralysis,” Lysyk said.
“It is imperative to develop alternative methods and products to prevent paralysis.”
Identifying the toxin responsible for paralysis is key to developing a vaccine or antiserum, which Lysyk said is the best control option. Through laboratory tick experiments, researchers have separated tick populations by levels of high virulence, low virulence and avirulence. The different tick populations can now be used for biochemical and genetic comparisons to identify the toxin and develop an antiserum, Lysyk said.
Other tick control methods include managing cattle to keep them out of tick-infested areas during tick season, removing rodent hosts, and controlled burns of infested areas. However, Lysyk said the cost effectiveness of these methods needs to be evaluated.
