Time to raid your cat’s stash
Northwestern
University
New collaborative research from Northwestern University and Lund University may have people heading to their backyard instead of the store at the outset of this year's mosquito season.
Often used as an
additive for cat toys and treats due to its euphoric and hallucinogenic effects
on cats, catnip has also long been known for its powerful repellent action on
insects, mosquitoes in particular. Recent research shows catnip compounds to be
at least as effective as synthetic insect repellents such as DEET.
But until now,
the mechanism that triggered insects' aversion to this common member of the
mint family was unknown. In a paper to be published March 4 in the journal Current Biology,
a team of researchers from Northwestern and Lund universities report finding
the underlying receptors that contribute to the mosquitoes' aversive reaction.
"Catnip and
its active ingredient, Nepetalactone, have been used for millennia to ward off
insect pests, at least since the time of Pliny the Elder," said Marcus C.
Stensmyr, associate professor at Lund University and co-corresponding author.
"But why Catnip is so potent on such a broad range of insect species has
remained unknown."
Traditional
approaches to mosquito control involved insecticides, but those eliminate other
insect species as collateral damage. Modern formulations of insect repellents
such as DEET target mosquito odor and taste receptors, rendering the insect
incapable of recognizing the chemical cues that signal a human prey.
"We discovered that Catnip and its active ingredient Nepetalactone activate the irritant receptor TRPA1, an ancient pain receptor found in animals as diverse as flatworms, fruit flies and humans," said Marco Gallio, an associate professor of neurobiology in the Weinberg College of Arts and Sciences. "We now think Catnip is so aversive to so many insect species because it activates this widespread irritant receptor."
In previous
work, the Gallio Lab and others demonstrated that humans, insects and many
other animal species possess a version of the transient receptor potential
ankyrin 1 (TRPA1) ion channel, a protein best known as the "wasabi
receptor" that senses environmental irritants like pain and itch.
"What is
particularly interesting is that, unlike wasabi or garlic compounds that also
activate these receptors in humans, catnip appears to selectively activate the
insect receptor," Gallio said. "This explains why humans are
indifferent to it, and provides a serious advantage for its use as a
repellent."
Why cats are so
attracted to catnip is an entirely different story and one that is not entirely
understood. Research indicates this may be due to an unusual interaction
between one of catnip's active ingredients and a molecular component present in
the reward system of the cat brain.
"Mosquitos,
in particular those that act as vector for disease, are becoming a bigger
problem as climate change creates attractive conditions for them farther north
and south of the equator," Stensmyr said. "Plant-derived compounds
represent a new emerging approach to developing insect repellents, as plants
have long known how to protect themselves from insect pests."
Gallio added
that plant-derived repellants are often available at a much lower cost and are
easier to obtain. Catnip's accessibility could have major implications in
developing countries where mosquito-borne diseases are a huge problem.
The Gallio lab
at Northwestern studies the sensory systems of the common Lab fruit fly
Drosophila, including the mechanisms that control the responses to external
temperature and pain. Lund's Stensmyr lab mainly focuses on mosquitoes and
other insect vectors of human disease.
The researchers
studied various insect species to better understand how catnip and its active
ingredient are working to repel a broad range of insects, while having no
irritant effect on humans.
To confirm their
results, the team ran a range of tests, including offering mosquitoes a blood
meal in a dish covered with a nylon sock doused in catnip, experiments
involving a wind tunnel, as well as experiments in which volunteers place their
hand in a cage with live mosquitos, with or without the protection of a catnip
oil rub.
Gallio believes
that the mechanism they discovered also provides proof of concept for the
development of next-generation repellents that exploit the same logic --
selectively targeting the mosquito irritant receptor.
"This is an
entry point to study how this molecule works on the receptor," he said.
"Once we understand its chemistry and how it interacts with the receptor,
we could design even more powerful and selectively targeted molecules."
The team's next
project? Finding out how to get rid of the cats that keep chasing them down.