Scent ‘camouflage’ keeps mice from destroying crops | Science

House mice may look cute, but they’re little monsters when it comes to crops. The rodents destroy 70 million tons of rice, wheat, and maize each year by devouring and infesting stored grain. They also dig up and eat the seeds farmers have planted.

Humans have been locked in a battle with these pests for millennia, using everything from cats to poisons. A new study may have found a better—and more humane—alternative: camouflaging fields with a scent that makes the seeds practically undetectable to mice.

It’s a “simple but elegant” solution, says Nils Christian Stenseth, a biologist at the University of Oslo and an expert of rodent impacts on crops who was not involved with the work. The approach, he says, could be applied to other crop pests such as insects and rats.

Mice rely on their sense of smell to find food. When it comes to wheat, that means sniffing out wheat germ, the embryo inside the seed that develops into the plant. House mice (Mus musculus) are an especially big problem in Australia, because they are not native. During years when their populations explode, the rodents can cause significant losses to the country’s $13 billion wheat harvest.

Farmers in Australia have mainly tried to control the mice with poisons and pesticides, says Peter Banks, a biologist at the University of Sydney. But these chemicals have to be reapplied often, which gets expensive. They can also kill birds and other wildlife.

In the new study, Banks and his colleagues modified a strategy that has proved successful in protecting endangered birds in New Zealand: throwing nonnative predators off the scent of their prey by robbing the scent of its meaning. In the New Zealand study, scientists smeared birds’ scents in places birds would never be found, such as piles of rocks. After a few days, cats and other predators began to view these scents as “misinformation.” When the native ground-nesting shorebirds arrived for their nesting season, the predators didn’t bother pursuing them even though they could smell them.

To try something similar for mice, Banks and his colleagues divided a wheat farm in rural New South Wales in Australia into 60 plots of 10 by 10 meters where wheat would be sown. The team sprayed unsown plots with wheat germ oil, hoping local mice would learn to associate wheat fields with a waste of their time and energy. In other fields, the team sprayed the soil with wheat germ oil after sowing, whereas other plots were left untreated.

Unlike in the New Zealand study, attempts to get the mice to see the wheat germ scent as a false signal largely didn’t work. Instead, “camouflaging” wheat fields with the scent did; in fields where the scent was overwhelming, the mice couldn’t seem to figure out where the seeds were. The camouflaged plots suffered 74% less damage than the untreated plot, the team reports today in Nature Sustainability.  

The equipment needed to spray the wheat germ scent on soil is part of common farm machinery, Banks notes, and wheat germ oil is an inexpensive byproduct of wheat milling. So the approach should be relatively easy to adopt by farmers, he says.

“This is a really nice piece of work,” says Peter Brown, a biologist at the Commonwealth Scientific and Industrial Research Organisation, an Australian government agency that funds and performs scientific research. Still, he says, the researchers need to figure out how much wheat germ oil farmers would need to apply—and how often—before the work can be translated to the real world. “Should it be applied every year, or just when mouse numbers are high at sowing? Lots of questions remain.”

House mice may look cute, but they’re little monsters when it comes to crops. The rodents destroy 70 million tons of rice, wheat, and maize each year by devouring and infesting stored grain. They also dig up and eat the seeds farmers have planted.

Humans have been locked in a battle with these pests for millennia, using everything from cats to poisons. A new study may have found a better—and more humane—alternative: camouflaging fields with a scent that makes the seeds practically undetectable to mice.

It’s a “simple but elegant” solution, says Nils Christian Stenseth, a biologist at the University of Oslo and an expert of rodent impacts on crops who was not involved with the work. The approach, he says, could be applied to other crop pests such as insects and rats.

Mice rely on their sense of smell to find food. When it comes to wheat, that means sniffing out wheat germ, the embryo inside the seed that develops into the plant. House mice (Mus musculus) are an especially big problem in Australia, because they are not native. During years when their populations explode, the rodents can cause significant losses to the country’s $13 billion wheat harvest.

Farmers in Australia have mainly tried to control the mice with poisons and pesticides, says Peter Banks, a biologist at the University of Sydney. But these chemicals have to be reapplied often, which gets expensive. They can also kill birds and other wildlife.

In the new study, Banks and his colleagues modified a strategy that has proved successful in protecting endangered birds in New Zealand: throwing nonnative predators off the scent of their prey by robbing the scent of its meaning. In the New Zealand study, scientists smeared birds’ scents in places birds would never be found, such as piles of rocks. After a few days, cats and other predators began to view these scents as “misinformation.” When the native ground-nesting shorebirds arrived for their nesting season, the predators didn’t bother pursuing them even though they could smell them.

To try something similar for mice, Banks and his colleagues divided a wheat farm in rural New South Wales in Australia into 60 plots of 10 by 10 meters where wheat would be sown. The team sprayed unsown plots with wheat germ oil, hoping local mice would learn to associate wheat fields with a waste of their time and energy. In other fields, the team sprayed the soil with wheat germ oil after sowing, whereas other plots were left untreated.

Unlike in the New Zealand study, attempts to get the mice to see the wheat germ scent as a false signal largely didn’t work. Instead, “camouflaging” wheat fields with the scent did; in fields where the scent was overwhelming, the mice couldn’t seem to figure out where the seeds were. The camouflaged plots suffered 74% less damage than the untreated plot, the team reports today in Nature Sustainability.  

The equipment needed to spray the wheat germ scent on soil is part of common farm machinery, Banks notes, and wheat germ oil is an inexpensive byproduct of wheat milling. So the approach should be relatively easy to adopt by farmers, he says.

“This is a really nice piece of work,” says Peter Brown, a biologist at the Commonwealth Scientific and Industrial Research Organisation, an Australian government agency that funds and performs scientific research. Still, he says, the researchers need to figure out how much wheat germ oil farmers would need to apply—and how often—before the work can be translated to the real world. “Should it be applied every year, or just when mouse numbers are high at sowing? Lots of questions remain.”