Killing mosquitoes means killing malaria parasites and preventing malaria infections - at least that's been the calculus for years. But in many countries insecticides aren't harming mosquitoes anymore.
More than 200 adults and children have gathered around a mosquito net. It is April in Burkina Faso and very hot and dry, which is a good thing in this west African country. When the rainy season starts soon, the number of malaria cases will explode.
The people from the village near Ziniare, 40 kilometers away from the capital, Ouagadougou, have gathered to listen to a community health care worker. He uses a megaphone to explain how to prevent mosquito bites.
He tells a young boy in a Burkina Faso football shirt to climb underneath the mosquito net and then demonstrates how to wrap the ends of the net underneath the mattress to make sure no mosquitoes can get inside.
But sleeping under a bednet is only one of the golden rules when it comes to malaria prevention. "If people are coming to your house to spray insecticides, let them do it," the healthcare worker said, adding that killing mosquitoes is the best way to prevent malaria.
A potent weapon losing its impact
The most popular insecticide to kill mosquitoes is DDT. It has proven so effective as an insect killer that some called it the "atomic bomb" of pesticides.
In 2001, however, it was banned from agricultural use under the Stockholm Convention because of its impact on wildlife, especially birds. Still, DDT remains important in fighting malaria in many African and Asian countries. People spray it on the walls of their houses, and mosquitoes die when they sit down to rest.
Spraying insecticides is also part of Burkina Faso's National Malaria Control Program. Minister of Health Lene Sebgo wants to halve the number of malaria cases in the country within five years. In 2013, the country with 17 million inhabitants recorded 7 million cases of malaria.
But DDT will probably not help to combat the disease in Burkina Faso, said Patrice Combary, coordinator of the National Malaria Control Program: "The mosquitoes have developed resistance to DDT. It does not kill them anymore. The situation is getting more and more serious."
Alternatives are too expensive
Cotton farms in Burkina Faso used DDT extensively in the past, Combary said. The insecticide should kill agricultural pests. But it also affected mosquitoes.
As DDT is ineffective now, Burkina Faso instead started to spray other insecticides, Combary said.
However, these substances, so-called carbamate insecticides, are very expensive.
"To spray 134,000 households, we have spend more than 500 million CFR, that is $1 million," Combary said. "It is too expensive. Definitely we are going to abandon this strategy."
Insecticides on bednets also affected
Bednets are impregnated with insecticides called pyrethroids. But according to Combary, in some regions of Burkina Faso resistance to them is already starting.
Researchers from the Liverpool School of Tropical Medicine reported in a study that one genetic change can make mosquitoes resistant to both DDT and pyrethroids at the same time.
"If you go to a place where you already have DDT resistance, you are likely to also have resistance against the insecticide that is commonly used for bednets," the study's author Charles Wondji told DW.
A worldwide problem
The situation is becoming dangerous in other countries as well. Resistances against modern insecticides are very common, especially in some parts of western Africa as well as in Sri Lanka.
"The more DDT - or other insecticides - are sprayed, the more mosquitoes develop resistance," Jürgen May of Bernhard Nocht Institute for Tropical Medicine in Hamburg told DW. "We expect that this will lead to a resurgence of malaria in some regions."
According to May, this trend was observed between 1990 and 2000 when DDT became less popular because of its impact on wildlife.
"Finding a new pesticide with a new mode of action would be the best solution," May added. "As the mosquitoes probably do not have mutations that makes them resistant against these new substances."
Looking for new insecticides
The Innovative Vector Control Consortium (IVCC) based at Liverpool School of Tropical Medicine has set the goal of developing three completely new insecticides.
"We now have more than eight candidates all showing high potential against mosquitoes that are resistant to existing insecticides," said Nick Hamon, CEO of the IVCC. "By the end of 2014, three will be tapped for full development.”
Hamon said if malaria-endemic countries have three new products that each take a different biological approach to killing mosquitoes, these countries should be able to keep mosquitoes under control for decades to come.
But, according to Hamon, the earliest date for these new products to reach the market is 2020.
That leaves Burkina Faso fighting malaria without the help of a proper mosquito-killing insecticide for at least six more years. At least, a bednet continues to provide good physical protection against mosquitoes - even if the insecticides on them become less effective.