We all know catnip to be one of the go-to treats for cats because of its effects on cat that make them all go sillier and dorkier than usual. Well, apparently this plant is also famous for its rather powerful impact on insects, particularly mosquitoes.
In fact, recent research shows catnip compounds to be at least as effective as synthetic insect repellents such as DEET.
It’s just that until now, scientists haven’t found out about the mechanism that triggered insects’ aversion to this common member of the mint family. Therefore, a team of researchers from Northwestern and Lund universities have found the underlying receptors that contribute to the mosquitoes’ avoidance to such compounds.
Co-corresponding author Marcus C. Stensmyr said, “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. But why Catnip is so potent on such a broad range of insect species has remained unknown.”
Compounds that make mosquitoes hate catnip
As we know, when we want to get rid of these blood-sucking baddies, we use insecticides; that’s the way it is conventionally from years ago until today. Modern formulations of insect repellents target mosquito odor and taste receptors, rendering the insect incapable of recognizing the chemical cues that signal a human prey.
Associate professor of neurobiology Marco Gallio said, “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.
“We now think Catnip is so aversive to so many insect species because it activates this widespread irritant receptor.”
Previously, 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. This substance is 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. This explains why humans are indifferent to it, and provides a serious advantage for its use as a repellent,” Gallio said.
Problem with blood-suckers
According to Stensmyr, mosquitoes are becoming bigger problem made worse by climate change. It creates viable conditions for them both in farther north and south of the equator and they can be a dangerous vector for disease.
“Plant-derived compounds represent a new emerging approach to developing insect repellents, as plants have long known how to protect themselves from insect pests,” said Stensmyr.
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.
And actually, that is an ongoing problem in some parts of the world; particularly dengue. Other than mosquito repellent, scientists have done efforts to combat the insects internally. Researchers from Spain, Portugal, and Colombia developed a model in order to better understand how Wolbachia bacteria can benefit certain areas.
Wolbachia, for those of you who may be asking what it is, is a type of bacteria that lessen the chances for the dengue virus to impact humans, which researchers discovered in 2009.
Now, these bacteria aren’t natural for the mosquitoes; there’s no way of the insect getting them in the surrounding environment. Researchers must introduce each bacterium in mosquitoes’ eggs, which are later released in areas affected by dengue transmission. And then, mosquitoes infected with Wolbachia naturally take over the local mosquito population.
Using a model to predict
The researchers use real data on human and vector activity in a framework that can be analyzed from a mathematical point of view, allowing them to re-create and understand the epidemiological situation.
Therefore, scientists can now identify those geographical areas with the greatest vulnerability. They have a better grasp of different levels of areas that prioritizes those where Wolbachia-carrying mosquitoes can have the strongest and most beneficial impact on the spread of the dengue virus.
Co-author of this study Jesus Gomez-Gardenes from Colombia said, “One might think that the most populated areas are those in which Wolbachia release would be most beneficial. However, this is not always true.”
According to the authors, once they immunize the most vulnerable geographical area, the ranking of the remaining areas is affected, giving rise to a new scenario that tells them where they should concentrate resources in the second instance and beyond.
This research will benefit a lot of people and groups, like the World Mosquito Program. It is currently releasing Wolbachia-infected mosquitoes to protect the global community from diseases such as dengue, chikungunya, yellow fever, and Zika.
In these kinds of initiatives, the information about the most vulnerable areas within cities or regions proved the researchers’ model could complement field studies to find targets that maximize the benefit for the whole community.
Gomez-Gardenes added, “Data-driven models have also proven useful to tackle the evolution and mitigation of other diseases such as COVID-19. Hopefully, the framework developed for dengue can be further generalized for tackling the control of other vector-borne diseases.”
Not just for mosquitoes?
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.
Basically, they wanted to find out if there are some species that have an aversive reaction to catnip without any irritant effect on humans, as well as understanding the plant’s active ingredient
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. They also experimented using a wind tunnel, as well as trials in which volunteers place their hand in a cage with live mosquitos, with or without the protection of a catnip oil rub.
According to Gallio, 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. Once we understand its chemistry and how it interacts with the receptor, we could design even more powerful and selectively targeted molecules,” Gallio said.
While it has a certain effect on mosquitoes, it’s not entirely understood why cats are so attracted to catnip. Research suggests that there may be an unusual link or interaction between one of catnip’s active ingredients and a molecular component present in the reward system of the cat brain.
Well, if it’s widely available around us in the future, just make sure that there are no cats around—otherwise you become the target of their zoomies.