Written by Finn Cameron Gillies Parker, Kathryn Price, Jenna Bytheway and Peter Banks, Conversation
For as long as humans have grown our food, we have battled animals against pests that destroy crops and take food for themselves.
The traditional method was to try to kill the pests with poisons. Often, however, this fails to kill enough pests, harms the local fauna, and only minimizes the damage.
We approached this problem differently by asking: How can we prevent hungry animals from finding our crops in the first place?
in Research paper published todayIn , we show how “chemical camouflage” can prevent house mice from finding newly planted wheat seeds. This method reduced mouse damage to wheat crops by more than 60% even during plague conditions, without killing a single mouse.
Rodents are to blame Estimated about 70 million tons of grain Lost around the world every year. Even cutting these losses by 5% could feed more than 280 million people.
In Australia, the rat plague of 2021 cost farmers in New South Wales alone more than $1 billion, according to Industry Association appreciation. A plague of rats occurs somewhere in Australia at least every four years.
Currently, the only management option for reducing rat populations is large-scale trapping. However, baits are often ineffective and have led to calls for more deadly poisons, which carry significant risks to local wildlife.
The relationship between trapping effort and crop yield is poorly understood, and rat populations usually collapse in plague years even without intervention. A better approach is to focus on reducing mouse effects, rather than mouse numbers.
How to trick a mouse
Mouse damage to Australia’s most expensive crop, wheat, occurs mostly in the two-week period between sowing and germination. During this time, the mice are attracted to the scent of wheat germ—the nutritious, fatty part of the seed—underground, and learn to dig the seeds in with extreme precision, which leads to huge crop losses.
This led to our question: Can we hide the seeds so mice won’t find them?
Like many animals, mice primarily use their sense of smell to find food. The world is full of odors, and hungry researchers should prioritize the important ones and ignore the unhelpful ones.
When food is hard to find, or when smell is not a useful indicator of food, foragers should Give up and find something else To avoid wasting energy.
Since hungry animals cannot afford to waste effort on odors that do not lead to food, they are so vulnerable Olfactory disinformation and chemical camouflage. As with visual camouflage, if the background appears, in this case the scent, like the item we’re trying to mask, then the target item can’t be discerned.
Animals can also recognize the usefulness of the information, which makes them vulnerable to another form of misinformation – prior exposure to the scent. By diffusing food scents before food is available, foragers who are initially attracted to the scent receive no reward and learn to ignore it.
When food is available, foragers do not follow scents because they know it is not rewarding. We recently used this technology to dramatically improve the nesting survival of threatened shorebirds at risk of predation by invasive predators in New Zealand.
Tested under harsh conditions
To date, these techniques have been tested on relatively widely dispersed feeds with fewer feeds over a larger area. It was not clear whether misinformation about the sense of smell could protect a crop containing more than 300 mice and 1.6 million seeds per hectare.
We worked on a 27-hectare wheat field in southwestern New South Wales, using 60 plots of land to test two olfactory misinformation techniques. We used wheat germ oil to provide the background for the aroma, as it is made from the part of the wheat seed that mice seek and is a relatively cheap by-product of the wheat milling process.
Both methods involved spraying a fine mist of a wheat germ oil solution onto plots. Each application was the equivalent of smelling about 50 times the number of seeds on the plot.
Our first technique, scent camouflage, was started immediately after the crop was planted and reapplied several times until seedlings emerged. This created a veil of wheat scent to hide the seeds from detection.
Our second technique, odor pre-exposure, was to apply wheat germ oil six days before the wheat crop was planted and continued for a week thereafter. We expected that rats that were attracted to the smell before they planted the seeds would begin to ignore the smell of wheat after not finding the seeds repeatedly.
We also had three control treatments: one that was sprayed with canola oil to control the effect of the oil, one that we walked without spraying to control seed loss due to trampling, and one that stayed completely intact.
After one and two weeks of cultivation, we counted rat damage in the form of fossils where the rats had extracted the seeds. After 2 weeks, we also estimated the number of seedlings that had lost mice. The results were amazing.
After 2 weeks, our camouflage and pre-exposure treatments reduced damage in mice by 63% and 74%, respectively, compared to the control group. We also estimated that 53% and 72% fewer seedlings, respectively, were lost to mice in these plots.
The difference in the effect of prior exposure to wheat odor and the effect of the camouflage treatments was not statistically significant, and we concluded that the camouflage effect was the most likely cause of harm reduction.
Working with animals
In a world with a growing population where food security is a priority, we need new ways to tackle pest problems sustainably and safely.
Our methods are simple, safe and highly effective, even during a plague of rats. It carries no risk to the local wildlife and does not involve killing. The mice also don’t starve – they simply eat the foods they ate before planting the wheat.
We believe that simple behavioral interventions like ours, which work with animals’ motivations rather than against them, are the way of the future in wildlife management and conservation.
We believe this new approach has the potential to manage the effects of pests without the side effects that come from using lethal pest control.
Finn CG Parker et al, Olfactory misinformation reduces wheat seed loss caused by rodent pests, Nature sustainability (2023). DOI: 10.1038/s41893-023-01127-3
the quote: How to Fool a Mouse: ‘Chemical Camouflage’ Can Disguise Crops and Cut Losses by Over 60% (2023, May 27) Retrieved May 27, 2023 from https://phys.org/news/2023-05-mouse-chemical- blur-crop-loss.html
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