An early start to controlling insects around livestock gives the best chance of minimising the annual population explosion of flies and midges that begins as soon as average daytime temperatures reach 10°C. That’s according to independent entomologist Dr Peter Bates of the Veterinary Medical Entomology Consultancy, who warns that delaying the start of control measures can mean farmers are playing catch-up and usually losing.
He warns against assuming that frosts in January and February could help reduce this summer’s insect populations. "Although air temperatures were below zero for several days running in many parts of the country, the larvae of some species relevant to livestock over-winter typically about 10 centimetres below the soil surface where frost may not have penetrated," he says. "So this cannot be relied upon to have killed insect larvae.
"Moreover, larvae of some species over-winter in woodland litter, where frost penetration is quite rare no matter how cold the weather. Then as soon as they hatch from pasture or woodland, blood-sucking species can migrate several kilometres to find livestock on which to feed."
While farmers cannot eliminate insect breeding sites from pasture and woodland, Dr Bates says a meaningful impact around farm buildings is possible by minimising open dung heaps, unscraped slurry puddles, and old hay and straw stacks.
"For maximum control, action must start before the insect breeding season," he advises. "Waiting until insects are bothering livestock allows breeding populations to become established and difficult to get on top of."
In conjunction with good farmstead hygiene, Pfizer VPS vet Andrew Montgomery says residual pour-on pyrethroid treatments such as deltamethrin (e.g. Pfizer Spot On™) or alphacypermethrin (e.g. Dysect Cattle Pour-On) are licensed to control insects for up to eight weeks depending on species and population.
His advice is that an early start to control measures can mean fewer treatments in total may be required, and therefore costs minimised. Financially, he also suggests there may be an upside because fly nuisance on cattle, for example, has been shown to reduce milk yields by up to 0.5 litres/cow/day or growth rates by 0.3kg/head/day.
Research into the use of insecticides against the Culicoides midge species, known to be implicated in the transmission of several viruses including Bluetongue and Schmallenburg, found a deltamethrin-based pour on treatment to be an effective control method. In the study, even hair clipped from the feet of cattle several weeks after standard treatment contained enough deltamethrin to kill the midges.
Mr Montgomery urges cattle and sheep producers to discuss insect control options with their vet or qualified animal health adviser.
