For many people, coffee is the perfect way to start the day, end a meal, or help to recover after a long weekend. But while humans may tend to love the bitter flavour -- usually with some cream and sugar -- some insects find it toxic.
One of these coffee haters is the mosquito, particularly the species Aedes albopictus, also known as the Asian tiger mosquito. It's not found in Canada but it can be found in pretty much any tropical area of the world as well as most of Europe and the United States. As with all mosquitoes, it's a pest and a bite can lead to a bump and that annoying itchiness.
But there's an even greater problem associated with this insect. It is a carrier of a variety of pathogens known to cause some serious viruses such as dengue, Chikungunya, and West Nile. All of these have the potential to cause long lasting infection and at times, death. The threat is so great many public health officials have sounded the alarm and brought viable control measures.
Insecticides may first come to mind but there is a problem. The mosquito has a wide range of habitats meaning it can grow both in rural areas as well as the urban environment. The risk to humans from these chemicals is simply too great and so it cannot be used. Something natural has to be used that will not only kill the bugs but also keep people safe. This essentially cancels out most known options.
But coffee has shown promise in the past. Back in 2003, it was shown to kill off the babies -- larvae -- of a cousin of albopictus, Aedes aegypti, the yellow fever mosquito. Although the mechanism wasn't entirely figured out, the authors at the time believed some of the chemicals in the black stuff blocked some of the important stages of development. They could not develop into adults. A closer inspection revealed some of the molecules mimicked those of insecticides. But the effect was far more dramatic and the insects could not develop resistance.
The push for coffee as a mosquito control measure increased in 2007, when a team used both coffee grounds and liquid infused with coffee to show the same effect on larvae. The concentration to achieve this kill was quite low, meaning there was no need to concentrate the product. The authors at the time suggested coffee could be a great way to prevent the mosquitoes from growing in gardens and other urban areas.
In 2012, the effects on Ae. aegypti were shown to be the same in Ae. Albopictus. In this case, the larvae were exposed to coffee extracts. Once again, the larvae were unable to develop and the population was killed off. It meant coffee could be used to keep both mosquito populations from getting out of hand.
Although these achievements revealed the importance of coffee, there was one problem. To control the populations, coffee would have to be spread in every stagnant water source. This presented a significant problem as finding each and every source would be impossible. There had to be a way to improve the chances a mosquito would choose coffee over regular water.
This past week, an international team of researchers may have found the answer. They conducted a similar study. But this time, they wanted to find out what made a female mosquito choose a certain habitat to lay eggs. What they found was that the answer may lay in colour.
The experiments were simple. The group first made coffee at two strengths, medium and high. They also used water as a control. They then offered the liquid to the mosquitoes to see if there was any choice made. The colour ranged from clear (water) to light brown-orange (medium) to dark brown (high). After the mosquitoes had had a chance to lay eggs, the team checked for any difference in choice.
The results were dramatic. The high concentration coffee had 90 per cent less eggs than in water alone. The medium had twice as many as the high but still paled in comparison to the water. To the authors, colour had to played a role and apparently, brown detracted the insects from laying eggs. If they did, the larvae died. The authors felt coffee could play a dual role in controlling mosquito populations. First, it would kill the larvae. Second, it could act as a deterrent to keep mosquitoes from laying eggs.
Granted, this wasn't the optimal conclusion as any clear water sources would be preferred. To achieve the best protection, coffee would have to be spread everywhere. But as the authors pointed out, there's already far too many unused grounds being simply discarded; they could instead be put to good use. This could both help the environment as well as decrease the likelihood of a bite and possibly of an unwanted disease.
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