A research team in Mali found a simple way to decrease the number of mosquitos that spread malaria — weeding. An invasive shrub gives the mosquitos most of the sugars that they need. Removing the flowers from the shrub reduced the number of mosquitos by more than half. It also got rid of the most dangerous mosquitos.

Though you may think that mosquitos only need blood, they actually also need sugar from plants for energy.

“Mosquitos obtain most of their energy needs from plant sugars taken from the nectar of flowers so we wanted to test the effect removing the flowers of the shrub Prosopis juliflora would have on local mosquito vector populations,” said Dr Gunter Muller, lead author of the study from Hebrew University Hadassah Medical School.

The invasive shrub in question is Prosopis juliflora, which is native to Central and South America. It was brought to Africa in the 1970s and 80s to reforest the area because it grows quickly. Unfortunately, this feature also makes it a notorious invasive species and it is now widespread across many countries in Africa. And it seems to be fuelling the mosquitos. The researchers decided to directly remove the flowers around villages in the Bandiagra District of Mali to see if that had any effect on the number of mosquitos.

The plant that fuels the malaria-spreading mosquitos, Prosopis juliflora. Image credits: B.navez.

First, the researchers assessed how many mosquitos were in nine different villages. Six of the villages had the invasive shrub and three didn’t. They used light traps to catch mosquitos in those villages to see how many there were. Next, in three of the villages with the shrub, they cut off all of the flowering branches (that must’ve been quite a job). They used light traps again to see if the number of mosquitos had changed.

The number of mosquitos found in the villages with the cut flowers decreased by almost 60%. Removing the shrub reduced the number of old female mosquitos, which are the main culprits in transmitting malaria parasites to humans. Their populations became similar to those in villages without the shrub.

Another co-author, Dr John Beier, from the University of Miami, summed up their research, “The presence or absence of Prosopis juliflora in villages has a significant influence on the size of the mosquito population in general, on their species composition, on the sugar feeding status and, the age structure of female populations. As well as offering a potentially environmentally reasonable and sustainable strategy in reducing the incidence of malaria, there are also other benefits to be gained from removal of these plants. For example, these plants are known to encroach on crop and pasture lands.”

So not only would removing this invasive plant reduce the number of deadly mosquitos, but also help local agriculture. Sounds like a win-win.

Journal reference: Gunter C. Muller, Amy Junnila, Mohamad M. Traore, Sekou F. Traore, Seydou Doumbia, Fatoumata Sissoko, Seydou M. Dembele, Yosef Schlein, Kristopher L. Arheart, Edita E. Revay, Vasiliy D. Kravchenko, Arne Witt, John C. Beier. The invasive shrub Prosopis juliflora enhances the malaria parasite transmission capacity of Anopheles mosquitoes: a habitat manipulation experiment. Malaria Journal, 2017; 16 (1) DOI: 10.1186/s12936-017-1878-9