One of the more ubiquitous of biting insects, mosquitos have been the scourge of nearly all humans throughout time. The can be found on almost every landmass bar Antarctica and a few subpolar islands, such as Iceland.
Due to the fact that the females are parasitic and tend to feast on the blood of vertebrates, they also have a tendency to becoming a vector for disease. In recent times, the Zika virus has gained plenty of attention in the press for its prevalence in Brazil in the lead up to the 2016 Olympic Games, but they’re also notable for spreading malaria, yellow fever, West Nile virus and dengue fever, with a variety of diseases found in different places around the world.
In Australia, there are some 5,000 reported cases of mosquito-borne Ross River virus and Barmah Forest virus each year. What’s worse, as seasonal weather patterns continue to become more erratic due to climate change, the populations of disease-bearing mosquitos also shift. This can result in people becoming exposed to diseases in areas it previously didn’t exist – potentially as close to home as their own backyard.
Throughout history, people have devised various methods for preventing mosquito bites, including the topical application of plant and animal-based oils. However, wearing protective clothing and the invention of mosquito nets have proven still more effective and, combined with the use of modern day repellents, we now have a series of practical defences against mosquito bites.
‘Chemicals’ Versus ‘Organic’
A PR agent representing a product called YaMate recently contacted Wild, offering us the opportunity of a trial. This product purports to use essential oils, plant extracts and other ‘natural’ ingredients, like citronella and lemon myrtle.
The YaMate product line includes a number of products, all specialised for a given application. There’s even a ‘Fishing Mate’ spray product, which includes a fish attractant with the aim of attracting fish while repelling insects.
Moreover, these products seem to have been tested by a variety of people that have gone on to sing its praises, including Dr Rhonda Melzer from the Queensland Parks and Wildlife Service, who is quoted as saying she uses YaMate to “repel march flies, mosquitos and midges”.
Given the strong testimonials, we accepted some products to trial from YaMate. As luck would have it, we had a tester, Bianca Dohnt, who planned on attending a festival in northern Victoria, mere days after the products arrived in the office. To be safe, we packed our tester off to her festival with the ‘X-Strong’ version of the YaMate repellent, which is made with soya bean oil, unprocessed beeswax, eco soy wax, xanthan gum and ‘a unique combination of essential oils and plant extracts’.
While you can read the resulting review elsewhere on the Wild website, we think this line sums it up, in which Dohnt responds to YaMate’s claim of being ‘non-toxic’: ‘Non-toxic to exactly what, however, isn’t specified. Certainly, the repellent proved to be non-toxic to mosquitos’.
Being very grateful that we’d found someone willing to subject themselves to dozens of painful bites all in the name of science, we then needed to discover why the product didn’t live up to its claims, as well as gaining a finer understanding of those substances that do seem to effectively repel mosquitos. But first, we wanted to find out why ineffective repellents should even exist. For this, we contacted Cameron Webb, a clinical lecturer and hospital scientist with the University of Sydney, who has written extensively on the topic of insect repellents.
According to Webb, products like YaMate maintain some popularity among consumers because of the belief in ‘natural’ and ‘organic’ products being somehow less dangerous for the user.
“I think people choose what they perceive to be natural products, particularly when it comes to products like insect repellents,” Webb explained. “They believe there’s somehow a risk inherent in the more effective options that contain substances like DEET – that they might be unpleasant to use or irritating.
“That opinion is misplaced.”
Webb is quick to point out that there are plant-based extracts and other traditional repellents that have been shown to have some effectiveness, but they are not nearly as effective as modern, targeted formulations. Nor should consumers think that just because something is marketed as natural or organic does it mean there’s no chance they’ll have a negative reaction to it.
“Formulations using DEET and picardin are used by billions of people worldwide, with the few cases of negative reactions caused as a result of ingesting, exposing the eyes and very young children.
“Just because you use something that contains an essential oil doesn’t make it safe and effective.”
DEET and Picaridin
In Webb’s words, DEET is considered the ‘gold standard’ in mosquito repellents because of its long history of efficacy, however there’s still no consensus on exactly how it works. However, whether it acts to ‘mask’ the users presence to mosquitos, or actively repels them, products using this substance have been shown to work.
However, there is a downside. DEET has been shown to damage plastic and rubber-based materials and textiles, and so users should avoid applying DEET-based products directly to synthetic clothing or rubbing it on to sleeping bags, camera housings and the likes.
Alternatively, picaridin was invented later than DEET, but has been shown to be equally effective. Even better, it is odourless and doesn’t appear to have the same damaging effect that DEET has on some materials.
More importantly, users seeking an effective insect repellent should be aware of the specific formulation of the active ingredient within the solution they’re buying. The given ‘strength’ of the repellent usually pertains to the percent of DEET or picardin present, and this will determine how often you should reapply to maintain the effects. For example, a DEET-based repellent at 80 percent concentration will continue to protect for more than 10 hours, providing it is not washed off.
Permethrin
Permethrin is a substance that’s used in a very different way to DEET and picaridin, as it’s an insecticide rather than a repellent. For this reason, it’s not traditionally used directly on the skin, but rather applied to clothing and mosquito nets.
“Clothing treated with permethrin causes exposed insects to die before they reach the skin, and they’re also used as a way to guard against ticks as well as mosquitos,” Webb says. “However, if you’re wearing a shirt treated with permethrin it won’t protect your exposed areas of skin. Use a topical repellent in conjunction with a treated garment.”
Pyrethroids
Pyrethroids are a class of chemical similar in composition to natural compounds found in some flowers that have been shown to be effective insecticides and are often used in smokeless mosquito coils.
“These devices are either plugged into a wall or battery-powered for use while camping,” said Webb. “The idea is that they knock down the mosquito before they have a chance to bite you.
“The benefit of these products is, unlike a traditional mosquito coil or citronella candle, you’re not breathing in any smoke and so there’s an argument to say they’re healthier.”
The effectiveness and safety of insect repellents and related products is assessed by the Australian Pesticides and Veterinary Medicines Authority (AVPMA). Any product claiming to be effective in deterring insect bites must be registered with the AVPMA and so more detail can be found via the organisation’s website.
For more information and guides to insect repellents in Australia, Choice also has a number of guides available.
This article was originally published in Wild issue 157. Subscribe today for your copy.