Grasslands National Park in Saskatchewan has a large population of black-tailed prairie dogs. (Parks Canada)

With the prairie dog population in Saskatchewan's Grasslands National Park dropping to less than half its normal size, officials are using insecticide to protect the rodents from disease-bearing fleas.

Parks Canada said Wednesday it will apply DeltaDust insecticide to the burrows of black-tailed prairie dogs in the park.

The idea is to kill fleas that could be spreading sylvatic plague to the park's population of prairie dogs, the only colony of its kind in Canada.

Earlier this year, one of the prairie dogs was found dead of plague, raising fears that more of the rodents could be affected.

Researchers have learned that the prairie dog population in the park is 50 to 70 per cent lower than the long-term average.

It's believed drought and predators are factors in the drop, but plague could be a factor, too.

"The fact that we've had one prairie dog probably suggests there's a few more," said Pat Fargey,  a species-at-risk biologist at the park, which is about 130 kilometres south of Swift Current.

"We don't know if that's a few tens of family groups. Is it hundreds of family groups?"

Although it's not believed the plague is actively spreading, any widespread infection could have a devastating impact on the prairie dog population, Parks Canada says.

Transmission to humans can occur through infected flea bites, but it's rare for people to contract the disease.

The park has been telling visitors not to walk through prairie dog colonies and to use insect repellent on their pants and shoes.