How Insect Repellents Workby Crysta Hammond
Written by: Sulayman Mehboob, B.Sc., M.Sc. - Microbiologist
Insect repellents are applied to the skin surface to inhibit biting insects from recognizing the person as their blood meal. Insects Repellents are often used against biting midges, mosquitoes, and ticks. They can be used against other blood-feeding arthropods like bed bugs and mites etc. They usually stop the insects from biting by either blocking the ways that help them to identify the host or by providing an odour that overrides that of the host. There is a large variety of insect repellents available which are categorized as either synthetic or botanical in nature.
Insect repellents act by interacting with Odourant Receptors (ORs) and the Gustatory Receptors (GRs) in mosquitoes. The mechanism of the insect repellents is that they bind to the “Odour Binding Proteins” (OBP) in the antenna of the insect and therefore make them move away.
Topical insect repellents are directly applied on the skin surface which interferes with the ability of the insect to complete the process of biting.
Area repellents provide protection from arthropod bites at distances that can exceed several meters.1,2
Insects like mosquitoes and ticks are attracted to the human skin odors and the CO2 we exhale. They also sense heat, movement, and visual cues to find a possible host.3,4 Repellents affect an insect's senses such as smell and taste to prevent it from finding a human or animal host. 5,6
How Biting Insects Find Their Hosts
In order to understand how insect repellents work, first we need to understand how biting insects find their hosts to feed. Research on mosquitoes has revealed that these insects use a combination of heat, smell, and sight to find their blood meal. They have the ability to sense the smell of carbon dioxide and lactic acid as well as other odours from the skin, and can also sense the warmth and moisture on the skin.
Mode of action of insect repellents. (A) Insects such as mosquitoes use chemical signals (shown as a green plume) to find their host and feed on them. Topical repellents (shown red plume) act at close range or on contact by disrupting the behavior of attraction. Spatial repellents show their effect at a much longer distance. (B) Insect repellents like Deet interact with multiple sensory receptors like Odourant Receptor (OR) or the Gustatory Receptor (GR) and the Ionotropic Receptor (IR) distributed on the various arthropod appendages.
Most insect repellents, including DEET, work on the principle of creating a vapor barrier that deters the insect from coming into contact with the skin. To the insect, the vapor has an offensive smell and tastes bad. Mosquito repellents work by altering the odour receptors.9
Currently under investigation by scientists with the International Anopheles Genome Project is the olfactory biology of the main malaria-carrying mosquito, Anopheles gambiae. In order to find a host to feed on their blood, mosquitoes use Olfactory Binding Proteins (OBPs) to sense specific human odors that are released by humans. Scientists believe that destroying mosquitoes’ OBPs can stop them from targeting the human body as hosts and effectively decrease bites.
Knowledge of the nature of receptor-ligand interactions is a promising alternative to three-dimensional studies since several OR-odourant/insect-repellent pairs have been characterized.10
Evidence suggests that the evolutionarily selected recognition site of ORs (primary site) is narrowly tuned to semi-chemical signals restricting, in theory, its tolerance for anything but its natural ligand.11
Food For Thought
A recent study shows that insect repellents interact with both the primary ("orthosteric") and the secondary ("allosteric") recognition sites. An insect repellent that has one or multiple AIs effective at small concentrations, especially of pharmaceuticals, will be of main importance since low AI use rate will improve all other characteristics.
Topical repellents having broad spectrum activity against the large number of arthropods will be useful considering that skin is our last line of defense. But spatial repellents with taxa-specific activity, targeting only specific groups of blood-feeding invertebrates will show limited targeted effects and they should not affect beneficial insects to mankind, like bees.
TotalSTOP is a DEET-free insect repellent utilizing Icaridin as an active ingredient. Icaridin is recommended by the World Health Organization (WHO), the CDC, and is EPA-Registered. It provides long-lasting, 12-hour protection from all kinds of ticks and mosquitos and 10-hour protection from black flies.
TotalSTOP is perfect for the whole family including individuals with skin sensitivities, children that are 6+ months, pregnant, and nursing mothers!
TotalSTOP is available in spray & wipes. It is non-toxic, odourless & water-resistant with a non-greasy formula that lasts all day.
About The Author:
Sulayman Mehboob, B.Sc., M.Sc. - Microbiologist
Sulayman has done research on various science projects and has been published in well reputed journals. Currently, he is doing research on animals and insects on various topics and some of his research projects have been completed and under review in the top journals. He loves researching plants and animals, and his aim is to continue deep study in this field.
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- Revay EE, Junnila A, Kline DL, Xue RD, Bernier UR, Kravchenko VD, Yefremova ZA, & Müller GC (2012) Reduction of mosquito biting pressure by timed-release 0.3% aerosolized geraniol. ActaTropica 124(1): 102–5.
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- Bohbot JD & Dickens JC (2012b) Odourant receptor modulation: ternary paradigm for mode of action of insect repellents. Neuropharmacology 62(5–6): 2086–95.
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- The Mysterious Multi-modal Repellency of DEET - Scientific Figure on ResearchGate. Available from: https://www.researchgate.net/figure/Proposed-hypotheses-for-how-insect-behavior-is-modulated-by-DEET-in-the-vapor-phase-A_fig1_280867419 [accessed 29 Apr, 2022]