LETHBRIDGE – The centuries old face-off between man and insect continues at a special facility at Agriculture Canada’s Lethbridge Research Centre.
As the only one of its kind in North America, the controlled-atmosphere building allows researchers like Doug Colville to investigate methods to manage troublesome livestock pests.
Chemical control works, but most insecticides were designed 25 years ago and no new significant ones have appeared since. Some have been deregistered because of environmental concerns and in some cases, resistance among parasites and insects has appeared so other controls are necessary.
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“We have been using drugs to control parasites for 25 years but we have not done a very good job of keeping track of how the parasite community has changed over time,” Colville said during a field day at the centre July 29.
As a livestock parasitologist, he and his team breed hordes of insects and parasites to see how they behave. They look at flatworms, tapeworms, biting insects and other parasites.
Some of the blood feeding pests are raised at the centre on the backs of selected cattle. The animals are only used for two weeks so they are not subjected to extended stress.
Researchers also monitor cattle behaviour when exposed to high levels of horn flies, stable flies and lice.
Flies and other biting insects are annoying and can cause stress and pain to an animal. A specially designed laser helps the scientists understand how much stress the animal is suffering.
Stress starts in a series of neurochemicals in the central nervous system that affect other parts of the body. High levels of stress lead to poor weight gain and productivity. For example, two stable flies per leg on a dairy cow lowers milk production.
“If they use energy to slap at flies, they are not using energy to produce milk or gain weight,” Colville said.
Besides chemical agents, vaccines and biocontrol agents like parasitic wasps are examined. Natural immunity among cattle is also studied as part of an integrated management approach that blends biological control with changes in practice in barns and pastures.
Predatory wasps work well if enough are released. It is important to get insects that work in local conditions. Sometimes the wrong species can be imported from the United States and they do not prey on the appropriate insect.
The researchers also know certain bacteria, when sprayed on standing water, can control some types of mosquito larvae.
For a time, ear tags carrying insecticides were effective, but now resistance has appeared. Colville suspects the tags were not used heavily enough to provide widespread control.
When studying pests, scientists have decided horn flies are the main challenge, followed by stable flies. Grubs used to be the greatest problem but they have been almost eliminated.
Horn flies hover in pastures from May to September. Adult horn flies feed on the blood of cattle, as often as several dozen times a day, and rarely leave the animal.
Research has shown moderate horn fly infestations reduce weight gains in untreated young cattle by 20 percent.
Because horn flies have developed resistance to some pesticides, researchers are investigating nonchemical methods of control.
The stable fly is found around dairies and feedlots. It has a blunt proboscis that hits the hide and sinks in a serrated edge so when it pulls out, it leaves a wound. The fly leaves saliva in the wound that is visible on the hide.
One method of control is to keep feedlots and manure piles as dry as possible.
Another area of study is tapeworms in horses. Researchers are assessing its prevalence, diagnosis and control.
“It is the predisposing factor to colic in horses,” Colville said.
The horse gut is susceptible to upset and if it ingests the parasite when grazing, it can cause inflammation in a join in the cecum to the intestine.
“If anything at all messes up where the cecum bends, it blocks the gut off and they get colic,” he said. “Colic is deadly to horses.”
Some troublesome problems from the past have almost disappeared because the agents have been killed with effective chemical treatments.
Sarcoptic mange is disappearing because of products like ivermectin. It is difficult to find the mites responsible for that condition anymore, said Colville.
It is a disease caused by the parasitic mite, Sarcoptes scabiei. The mite burrows deeply into the skin, causing intense itching, hair loss and exposed skin.
Cattle affected by sarcoptic mange lose grazing time and do not gain weight as rapidly as uninfected animals.
Chorioptic mange, or tail head mange, is appearing more often because it comes from a different mite. It feeds on the surface and drinks the fluids that leak out. It can cause hair loss and irritation but is not as damaging as sarcoptic mange.
“For some reason it is more common than it used to be,” Colville said.
“It seems to be sneakier and it seems to get away on producers more easily.”
