The new finding stems from Northwestern University and Lund University. The hunt for new repellents is important given the problems presenting by mosquitoes, especially acting a disease vectors. Diseases of concern include Malaria Lyme, Zika, West Nile, and chikungunya diseases.
Moreover, new types of diseases are being identified that mosquitoes can carry. There is also an increase in mosquito activity due to climate change, which sees more mosquito populations moving northwards.
Catnip
Catnip (Nepeta cataria) is a plant of the mint family, with downy leaves, purple-spotted white flowers, and a pungent smell attractive to cats.
Catnip is added to some cat toys, as well as to some pet foods, and it will sometimes trigger a euphoric and hallucinogenic effect on cats. The reason why cats are attracted to catnip rests on an interaction relating to catnip’s active ingredients and a molecular component that lies within the reward system of the cat brain.
Catnip as a repellent
Catnip also has another property. This is as a repellent against insects, and especially in relation to mosquitoes. A further advantage is that the end product is derived from natural sources. Given that catnip has been shown to be of equivalent effectiveness as synthetic insect repellents, including DEET, there will be considerable interest in a catnip based product.
DEET – the synthetic alliterative
DEET (or diethyltoluamide) was developed in 1944 and it is most common active ingredient in insect repellents. DEET is a yellow oil-like substance, and it is applied to surfaces or to clothes to provide some protection against mosquitoes, and other pestilent insects.
DEET targets mosquito odor and taste receptors, which means that the flying insects are not able to detect humans and hence people protected by DEET are not classed as potential prey to be bitten.
In terms of safety, DEET is regarded as not presenting a health concern provided DEET containing products are used as stated on the label. That includes label recommendations for how to use these products on the face (spray on hands and use on hands to apply it to the face, as an example).
Why does catnip work against insects?
What has challenged scientists is with identifying the precise mechanism within catnip that produces an aversion with an insect. Catnip is part of the mint family, but is possesses something that other mints do not.
The new research has identified an active substance called nepetalactone. The chemical is activating the irritant receptor TRPA1, which is an ancient pain receptor found in animals. With mosquitoes, catnip acts as a widespread irritant receptor. People, however, are indifferent to the effects of the chemical.
Possible solution
The new compound also offers something that is environmentally more sustainable, through a plant-derived compounds. The costs are also likely to be lower, give the ease of growing catnip.
A further cost and production issue is that lower quantities could be used. Most commercial insect repellents contain about 5 percent to 25 percent DEET. With the alternative product, much less catnip oil would be needed in a formulation to have the same level of repellency as a DEET-based repellent.
The developmental product was tested through various experiments. For example, in one part of the research mosquitoes were offered a blood meal in a dish covered with a nylon sock doused in catnip.
In another study, volunteer subjects agreed to place their hand in a cage with live mosquitos. In some cases the hands were protected with either a catnip oil or DEET; in other cases there was no protection.
In the finished form, oil isolated from catnip by steam distillation can be turned into a repellent against insects.
Next steps
The next step is to develop a new form of sustainable insect repellents that will exploit the same logic drawn out from the experiments, which targets the mosquito irritant receptor.
The research has been published in the journal Chem Catalysis, in a paper titled “Chemo- and stereoselective intermolecular [2 + 2] photocycloaddition of conjugated dienes using colloidal nanocrystal photocatalysts.”
Essential Science
This article forms part of Digital Journal’s long running Essential Science series. Each week we take a more detailed look at an important and topical science subject.
Last week the subject was soft robotics. For super-sensitive touch to advances in soft materials that curls under pressure or expands when stretched, such innovations in materials science are enabling soft robotics to be advanced.
Digital Journal considered look at three advances in the field.
The week before, the subject was three recent research papers that explore the mysteries of black holes. Of particular interest are the ‘supermassive’ blackholes. These contain between a million and a billion times more mass than a typical stellar black hole. The only mechanism capable of producing such enormous amounts of energy is the conversion of gravitational energy into light by a massive black hole.
