Mosquito Control

Azolla is known as the ‘mosquito fern’ due to its ability to reduce mosquito breeding populations by more than 95%. It does this by covering the surface of sluggish, still or stagnant freshwater bodies, preventing adult mosquitoes from laying eggs and also reducing the emergence and development of mosquito larvae. This lowers the threat of mosquito-transmitted epidemics and potential pandemics such as malaria, chikungunya, dog heartworm, dengue, yellow fever, eastern equine encephalitis, St. Louis encephalitis, La Crosse encephalitis, western equine encephalitis, west Nile virus and, most recently, the Zika virus.


The Zika virus initially causes a mild illness known as Zika fever, which has been known to occur within a narrow equatorial belt from Africa to Asia since the 1950s. In 2014, the virus spread eastward across the Pacific Ocean to French Polynesia, then to Easter Island and in 2015 to Central America, the Caribbean, and South America, where the Zika outbreak has the potential to reach pandemic levels in 2016 (Fauci & Morens, 2016). (See below for reference citations)

The threat is amplified because the Zika virus is passed by pregnant mothers to their unborn child, resulting in possible microcephaly in new-born babies.

The relationship between the Zika virus and microcephaly in new-born babies was first observed in 2015 in the Barao de Lucena Hospital, Recife, northeastern Brazil. This was subsequently confirmed and in January 2016, Colombia, the Dominican Republic, Ecuador, El Salvador and Jamaica advised women to postpone getting pregnant until more is known about risks associated with the Zika virus (BBC News, January 23 2016).

In January 2016, the UK government and the U.S. Centers for Disease Control and Prevention (CDC) also issued travel guidance to countries affected by the Zika virus, including advice for pregnant women to consider postponing travel to those counties.


The Zika virus is transmitted by the tropical mosquito Aeded aegypti and also possibly by the mosquito Culix, which is more widespread and up to 20 times more common than A. aegypti. This has major global implications, with estimates of up to four million people becoming infected in the Americas in 2016 (BBC news 28 January 2016) and the virus reaching pandemic proportions the same year.

There is no known cure or vaccine for the Zika virus, so that the only way to mitigate the threat at present is to reduce populations of the mosquitoes that transmit the virus.

mosquito horizontal

Above left to right: Photographs of mosquito larvae, mosquito emerging from pupa, and adult mosquito.


Azolla is one of the fastest growing plants on the planet, doubling its biomass in as little as two days. It is able to do this without the need for nitrogen fertilizers due to its symbiotic cyanobacterium, Anabaena azollae, which assimilates the nitrogen needed for azolla’s rapid growth directly from the atmosphere.

Azolla’s ability to reduce mosquito populations and related diseases has been confirmed by in-house research at the Azolla Foundation, by its sister organization, Azolla Biosystems Ltdand by the following published studies.

In the Indian city of Ghaziabad, close to New Delhi, breeding of malaria-transmitting mosquitoes was almost completely suppressed in pools, wells and ponds covered with azolla (Ansari et al.,1991). Similarly, in southern India, immature mosquito populations were significantly reduced by mats of azolla covering the water in rice paddies (Rajendraan & Reuben, 1991).

In Africa, Mwingira et al. (2009) showed that azolla reduced oviposition and adult emergence of mosquitoes in Tanzania, due to strongly reduced larval productivity in sites with high (more than 80%) azolla cover of the water surface. In Kenya, Okech et al. (2008) also demonstrated that  azolla is able to form a dense canopy in rice paddies, ‘choking mosquito larvae while nourishing the growth of rice’.

azolla rice-horz

Above: Photographs of azolla forming a dense mat on the surface of water. Left, azolla grown in a rice paddy. Centre, azolla grown in a container, Right, detail of the dense mat of azolla.

The reduction of mosquito populations can be enhanced by the addition of freshwater fish, such as carp or tilapia, which feed on the mosquito larvae and azolla plants, providing a local, renewable source of high-protein food.

The presence of azolla on the surface of water bodies does not have a detrimental effect on water quality. Azolla actual has a beneficial effect by improving water quality.


Azolla’s suppression of mosquitoes is particularly important because the plant also cleans and purifies stagnant and waste water, including harmful toxins, thus reducing illnesses due to unclean or contaminated water (Costa et al., 1999, 2009; Muradova et al., 1991). A low-cost, sustainable system to do this by individuals or communities has been developed by Foundation Associate Alan Marshall in conjunction with Azolla Biosystems.

The plant biomass resulting from its reduction of mosquitoes and water purification can be used as a local, renewable biofertilizer or feed for domesticated and agricultural livestock in both urban and non-urban locations.

Scientists at the Azolla Foundation and its sister organization, Azolla Biosystems Ltd, are available for consultation to aid governments and other organizations who are working to reduce outbreaks of the Zika virus.

Please contact us for details.


Ansari, M. A. & Sharma, V. P. 1991. Role of azolla in controlling mosquito breeding in Ghaziabad District villages (U.P.). Indian J. Malariol., vol. 28, pp. 51-54.

Costa, M.M., Conceição Santos, M & Carrapiço, F. 1999. Biomass characterization of Azolla filiculoides grown in natural ecosystems and wastewater. Hydrobiologia, vol. 415, pp. 323–327.

Costa, M.L., Santos, M.C., Carrapiço, F. & Pereira, A.L. 2009. Azolla-Anabaena’s behaviour in urban wastewater and artificial media – Influence of combined nitrogen. Water Research, vol. 43, pp. 3743-3750.

Fauci, A. S., & David M. Morens, D.M. 2016. Zika Virus in the Americas — Yet Another Arbovirus Threat. The New England Journal of Medicine. January 13, 2016. DOI: 10.1056/NEJMp1600297

Muradov, N., Taha, M., Miranda, A. F., Kadali, K., Gujar, A., Rochfort, S., Stevenson, T., Ball, A. S., and Mouradov, A. Dual application of duckweed and Azolla plants for wastewater treatment and renewable fuels and petrochemicals production. Biotechnology for Biofuels 2014, vol. 7:30, pp. 1-17.

Mwingira, V. S., Mayala, B. K., Senkoro, K. P.Rumisha,  S. F., Shayo, H.,  Mlozi, M. R. S. & Mboera, L.E.G. Mosquito larval productivity in rice-fields infested with Azolla in Mvomero District, Tanzania. Tanzania Journal of Health Research, vol. 11, no. 1, January, 2009, pp. 17-22.

Okech, B.A., Mwobobia, I. K., Kamau, A., Muiruri, S., Mutiso, N., Nyambura, J., Mwatele, C. Amano, T. & Mwandawiro, C. Use of Integrated Malaria Management Reduces Malaria in Kenya. PLoS ONE. 2008; 3(12): e4050. Published online 2008 December 30. DOI:  10.1371/journal.pone.0004050

R. & Reuben, R. 1988. Laboratory evaluation of the water fern,Azolla pinnata for mosquito control. L Biol. Control, vol. 2, pp. 116-116.