“Instead of just looking at straight kill effects, you’re looking at subtle effects, behavioral effects, long-term effects,” Lucas said. “In the old days you sprayed an insect and if it wasn’t dead in a day you’d say the product is useless.”
But the emergence of new products is hindered by the expense and burden of safety and efficiency trials needed for gaining a WHO recommendation, which major aid organizations require.
“These trials take time, they take a huge amount of money,” Lucas said.
Gaining approval for reformulations of existing pesticides takes at least a couple years and around $1 million. And that path is streamlined compared to the process for completely new chemicals, which can cost “certainly $100 million to bring a new product to market," he said.
As a result, new insecticides will probably not be available for malaria control programs until around 2022, Lucas said.
The WHO is aware of the bottleneck and has created an advisory group to examine new vector control paradigms, Mnzava said.
“This will also help in shortening the process to review new products,” he said.
Some public health scientists, however, say new insecticides should be thoroughly studied before they are approved. Citing the example of pyrethroids, University of California, Berkeley epidemiologist Brenda Eskenazi, a pesticide expert, said “virtually nothing is known about the human health effects… I’m astounded that there’s been very little human research.”
"Green" ways to kill mosquitoes
To many malariologists, this latest round of resistance gives proof that the long-standing reliance on synthetic chemicals to fight malaria can’t continue.
“The agencies hate to hear this… the nets are still effective, but I think the handwriting is on the wall,” said Gregory Lanzaro, a medical entomologist at UC-Davis and expert in the genetics of malaria-transmitting mosquitoes. “Nobody’s pooh-poohing the idea of using bed nets. They’ve saved many, many lives. They’ve worked very well. But the thing is, they’re not sustainable. They’re going to have to be replaced by something else.”
New insecticides are not the answer, Lanzaro and others say, because the mosquitoes will just adapt again.
“It’s a living system and if you poke it, it responds,” Lanzaro said. “We need completely new strategies.”
One approach researchers are working on is genetically engineering mosquitoes to be impervious to the malaria parasite. Another is infecting mosquitoes with bacteria that fight off invading protozoa. While promising, these methods are still in the experimental stage.
“Green” environmental management tactics are proving very successful in some areas.
Draining ditches and removing weeds to eliminate places for mosquitoes to breed – traditional practices largely abandoned with the advent of DDT – helped cut malaria cases by more than half in Mexico and Central America in recent years. Some Mexican states control mosquitoes that breed in algae-covered ponds by skimming the water once a week. Other places, including many parts of the U.S. and Europe, treat breeding sites with biological agents that kill insect larvae.