Population halved in three months
By Alice Klein
It is pest control without poison. A new type of bait that stops rats from having babies is helping to tackle infestations in several US cities.
The bait – known as ContraPest – was approved by the US Environmental Protection Agency last August. It makes rats infertile by triggering early menopause in females and impairing sperm production in males. There are no side effects and the rats eventually die of natural causes.
The technique is considered more benign than other control strategies being investigated, such as gene drive, which can be used to spread infertility genes through pest populations. A recent report by the US National Academies of Sciences warned that gene drive could have unforeseen consequences.
The first field trial of ContraPest, conducted in the New York City Subway in 2013, halved the resident rat population in three months. Two more trials have now been completed in the US – one at a large-scale farm and one in an urban area – both in East Coast cities.
Rat numbers at the farm fell by one-third over three months. In the urban area, population growth was suppressed during the peak breeding season so that the population expanded at only one-third the expected rate.
“You’ll never wipe out rats completely – they’re too smart,” says Brandy Pyzyna from SenesTech, the biotechnology company in Arizona that developed the bait.
Fast breeders
“But if you think about it, one breeding pair of rats can produce 15,000 pups in a year,” she says. “Even if you can reduce that by a third in a few months, you’re already talking 5000 fewer rats, and the population will continue to go down.”
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