Icipe finds that locust and cricket oil can fight mosquitoes

Locusts. Their oils often go to waste when the insects are used for other purposes.

Kenyan researchers suggest one secret to fighting off mosquitoes may lie within the bodies of other insects.

A new study reveals that extracting oil from termites and locusts, then mixing it with common plant-based repellents, doubles the effectiveness of these natural repellents.

This eco-friendly discovery comes at a critical time. In Kenya alone, malaria is responsible for roughly 3.5 million new clinical cases and more than10,000 deaths every year. Furthermore, mosquitoes are increasingly developing resistance to the synthetic pesticides currently used on bed nets.

The combination is as powerful as commonly used synthetic chemicals that the world is trying to eliminate, according to scientists from the Kasarani-based International Centre of Insect Physiology and Ecology (Icipe).

Synthetic chemicals are effective, but they sometimes cause skin irritations and allergic reactions and so a natural replacement is safer.

“Botanical repellents derived from natural sources such as citronella, neem, eucalyptus and lemongrass oils are increasingly favoured due to their biodegradability, ecological safety and consumer preference for natural products,” the researchers wrote in a paper published last week in the Scientific Reports journal.

The problem with many plant-based repellents, however, is that they evaporate too quickly and so provide only limited protection.

The researchers theorised that because insect oils are heavy and stable, they can trap the active plant scents and release them slowly over time instead of letting them vanish into the air all at once. It is similar to how a high-quality perfume uses certain base oils to make the scent last all day.

“Yet, their potential role in extending the protection duration, improving adherence and stabilising natural repellents has not been systematically investigated,” they wrote in their paper titled “Harnessing insect-derived oils for enhanced efficacy of plant-based repellents against disease-transmitting mosquitoes.”

The Icipe team, led by senior research officer Dr John Ochola, used standard laboratory techniques to extract oils from desert locusts, bush crickets and termites. These insects are already farmed for food, and the oils are often a byproduct of that process that would otherwise go to waste.

The plant essential oils, such as citronella and lemon eucalyptus, were extracted separately using similar methods.

Dr Ochola’s team then mixed the plant and insect oils together in different proportions.

To see if the blend actually worked, a small amount of the blend was applied to volunteers’ arms, which were then exposed to a cage full of hungry, disease-free mosquitoes.

Researchers measured the Complete Protection Time (CPT), which is the length of time before a mosquito finally lands and tries to bite.

This study's breakthrough was using insect oils to make those natural scents "stick" to the skin longer.

 In these tests, the 50-50 termite and citronella mix kept mosquitoes away for about three and a half hours. This is nearly identical to the protection time of the chemical repellent DEET, the world’s most widely used synthetic chemical used for for repelling biting insects such as mosquitoes.

The researchers said insect oils are not only effective but also eco-friendly. These oils are often a byproduct of the growing edible insect industry that raises insects for food and animal feed. Instead of throwing the fats away, they can be repurposed into life-saving medical products, they said.

The goal is to ensure the protection is reliable enough to prevent the transmission of dangerous parasites.

"In addition to repelling or killing the mosquitoes, they could prevent human-mosquito interaction and prevent the transmission of malaria parasites or other vector born disease, ensuring protection is long enough to avoid mosquito bites and disease transmission,” the researchers said.