"Everything in my life involves mosquitoes," Bart Knols says. "They're my passion."
© Manon Bruininga

This scientist is the ultimate mosquito killer

There is only a faint glimmer of blue light on the stage, barely illuminating the man who just sat up in bed. A mosquito can be heard buzzing about, then a slap. "Gotcha," the man says. As the lights go up, he points to a blood fleck in the palm of his right hand. The location is Maastricht, the Netherlands, and the man is Dutch entomologist Bart Knols. Still in bed, he stares at the audience through his round glasses. "Mosquitoes. I hate them," he says. "Don't you?" Then Knols gets up, and, dressed in boxer shorts and a polo shirt, delivers a 10-minute talk entitled "Three new ways of killing mosquitoes."

Knols has studied mosquitoes for a quarter-century. He seems to have come up with a new way of killing them every other year. In the 2012 TEDx Talk, he presented three ideas: simulating human odor to lure mosquitoes into traps; teaching dogs to recognize the smell of mosquito larvae, so they can sniff out breeding sites; and flooding human blood with a drug that kills mosquitoes when they bite.

Knols has since championed other schemes; using drones to spray insecticides, for instance, or letting a fungus kill mosquitoes. His latest plan, modifying African houses to become big mosquito traps, is now being tested in a huge, $10 million trial. In humanity's war with mosquitoes, Knols is one of its most creative warriors.

And creativity is needed. Despite decades of research, mosquitoes are still the deadliest animals in the world, spreading diseases that sicken hundreds of millions of people annually and kill more than 600,000. Decades-old insecticides are still the most important weapon. "Where is the innovation?" Knols asks.

Turning a house into a trap

A big study in Ivory Coast seeks to kill mosquitoes by bricking up the open space under the roofs of houses and installing eave tubes that have an insecticide-coated net on the inside.

C. Bickel/Science

His obsession has led to an unusual career. Knols has won both the Ig Nobel Prize, a spoof award for unusual or trivial research results, and the prestigious Dutch Eijkman Medal for tropical medicine. He has an impressive list of high-profile publications, but feels academic science doesn't nearly have enough impact. That's why in 2012 he left Wageningen University and Research (WUR) in the Netherlands to co-found a startup named In2Care, which sells human odor-baited mosquito traps. Knols is also the Dutch media's go-to guy for mosquito stories. He combines sometimes-dire predictions about the threat of mosquito-borne disease with what some call a knack for public engagement. Others call it a knack for self-promotion.

Many say Knols can be difficult to get along with, and he has a history of getting into tussles with collaborators. Just last month—after Science had interviewed him—Knols announced that his relationship with In2Care would soon end. "I think one of Bart's key strengths is his energy and commitment to make change and ultimately save lives," says entomologist Matthew Thomas of Pennsylvania State University (Penn State), University Park, who leads the mosquito trap trial in Africa. "The downside is that his doggedness can ruffle feathers."

Knols started making headlines early on. As a Ph.D. student at WUR, he and his colleague Ruurd de Jong tried to find out which human odors attract mosquitoes. "Man, we turned the lab into a smelly place," Knols says. They lured mosquitoes with everything from pads worn under their armpits or in their groin area to used tampons. One day Knols put his worn socks on top of a cage. "These things went crazy for it," he says. Feet often have a cheesy odor, so the next question seemed natural: Does cheese work as bait? As it happened, mosquitoes found cheese from Limburg, the southern province where Knols was born, particularly irresistible.

It was vintage Knols: quirky research with a serious core. "The bacteria that create the aroma of some of these smelly cheeses may actually originate from human skin, and therefore you may attract malaria mosquitoes with the aroma," he says. When Parasitology Today published the study in 1996, Knols also penned a letter in The Lancet, bragging that medical entomologists were now taking cheese with them around the globe. "Whether or not they will manage to attract another mosquito species with Limburger cheese remains to be seen," he wrote; "(if not, they can always eat it.)"

Journalists around the world loved it—as did the Ig Nobel jury—but the study's impact on the field was modest, some scientists say. "It's a nice story, but you wouldn't use cheese to catch mosquitoes," says Janet Hemingway, an entomologist at the Liverpool School of Tropical Medicine (LSTM) in the United Kingdom. Today, scientists are still working on a good attractant for malaria mosquitoes, she notes. Knols says they are still testing blends based on his work with cheese.

After getting his Ph.D., Knols worked at the International Centre of Insect Physiology and Ecology (ICIPE) in Nairobi for 5 years, three of them leading the malaria program at a field station in Mbita Point, Kenya, on the shores of Lake Victoria. In 2003, he joined the International Atomic Energy Agency in Vienna, which has a long-running research program that uses radiation to create sterile insects, which can help reduce natural populations. He went back to WUR in 2006.

"Everything in my life involves mosquitoes. They're my passion," Knols writes on his website. "I love to research them. But I prefer to eliminate them." His torrent of proposals for doing so elicits mixed reactions. "He is adopting a bit of a shotgun approach," says LSTM entomologist Philip McCall. "Maybe if he had fewer, refined weapons, he might press people more" to try them. But Andreas Rose, an entomologist at Biogents, a company in Regensburg, Germany, sees his prolific creativity as a strength, though he notes that Knols at times unwittingly adopts other people's ideas as well. "He's like a composer who maybe has heard a melody on the radio that he then incorporates in his work," Rose says.

Knols's media presence has raised eyebrows among colleagues, and some find him too alarmist. He often warns about the threat of epidemics and exotic mosquitoes; when the Asian bush mosquito (Aedes japonicus) showed up in the Netherlands, for instance, Knols said it might be able to transmit Zika, and, if so, a major door-to-door eradication effort would be called for. "Sometimes we are watching with surprise how strongly he asserts things," a spokesperson for the Dutch National Institute for Public Health and the Environment told the newspaper NRC Handelsblad.

After looking at some houses, we just sat down in the shade of a mango tree and started brainstorming.

Andreas Rose, entomologist at Biogents in Regensburg, Germany

​Knols is an admirer of Fred Soper, a legendary U.S. scientist at The Rockefeller Foundation who in the late 1930s helped Brazil get rid of a massive infestation of Anopheles gambiae, Africa's main malaria vector. An authoritarian figure, Soper hired thousands of workers in a military-style campaign to fumigate buildings and treat breeding sites with a poison called Paris green. "Soper had the willpower, the passion, the energy and the leadership qualities necessary to carry out a campaign in such a large area," Knols wrote in a 2009 book.

He is a force to be reckoned with himself. "He is uncompromising and he pushes a singular Knolsian view of the world," McCall says. "His approach to getting traction is to really push ideas hard," Thomas says—and sometimes the rhetoric gets ahead of the science. "His contribution is as an agent of change and someone who is trying to shake the system up."

His stint at ICIPE ended in a dramatic fashion after he accused a fellow scientist of misconduct, a claim then-ICIPE Director-General Hans Herren dismissed. Herren says he fired Knols for insubordination and called in the police after Knols blocked the main entrance at Mbita Point, essentially trying to take control of the station. "It was a pity really, because Knols had great ideas. But you can only tackle malaria by working together." Knols says Herren must be confused about the 14-year-old incident: "I never ever was involved in any protests or demonstrations," he says. Both say they have since buried the hatchet.

Irish entomologist Gerry Killeen resigned from ICIPE at the same time to protest Knols's dismissal. "Am I always thrilled about the way Bart approaches myself or other people? No. But it doesn't mean that he's wrong," he says. Killeen, now at the Ifakara Health Institute in Dares Salaam, Tanzania, says Knols fostered a great atmosphere at Mbita Point. "People felt they were really doing something; that they could make a contribution, develop as scientists, and compete globally."

Knols's most ambitious project so far brought both his talents and problems into sharp focus. In 2012, In2Care partnered with Biogents, Penn State, and others on an EU-funded project to develop a new way to kill mosquitoes. The partners met in Tanzania in February 2013 to discuss the project. "After looking at some houses, we just sat down in the shade of a mango tree and started brainstorming," Rose recalls. One result was what's now called the "eave tube." African houses often have open eaves, which mosquitoes use as an entryway. The idea was to brick off these openings and install a few polyvinyl chloride, or PVC, tubes, open to the outside to allow mosquitoes in; inside the house, the tubes are closed off by an electrostatic netting coated with an insecticide.

An eave tube, a PVC tube with an insecticide-coated net inside. Scientists hope that fitting houses with such tubes can drive down malaria.
© Manon Bruininga

The concept unites several ideas. Instead of a chemical attractant, it uses the humans in the house as bait. The netting—originally developed to filter pollen out of the air—gives insecticide particles an electric charge, making them stick better to the insects. The idea is "brilliant," Killeen says. "I wish I had thought of that." In 2014, the first eave tubes were tested in houses in Tanzania. After the EU project ended, the partners secured $10 million from the Bill & Melinda Gates Foundation for a randomized controlled trial in Ivory Coast. In 20 villages, houses are being equipped with eave tubes, while villagers receive insecticide-treated bed nets; 20 other villages get only bed nets. The team will test blood samples from 50 to 60 kids per village for malaria every 2 weeks. Results should be in by 2019.

It would seem like the chance of a lifetime for Knols—an opportunity to see at least one plan all the way through a large trial. But his apparent conflict with In2Care has made further involvement unlikely. The company says Knols is no longer working for it, but its co-founders—including two younger entomologists trained at WUR—declined to answer questions. Knols himself says he will leave in the near future but provided no details. "I'm a man who is constantly on the search for new things, and I explore things," he says. "And that is not always what other people like—let's put it that way."

In his 2009 book, Knols drew a sobering conclusion about his academic work until then. "I doubt whether the knowledge I added has saved the life of even one African child," he said. Seven years later, he's more optimistic: With the traps and the eave tube project, "I strongly feel that we have made contributions to public health improvement."

But much more is possible, he says. The problem with today's mosquito control is that it suffers from too much talking and increasingly relies on "community participation," which is difficult to sustain, Knols wrote in his book; he scorned Aruba, where during a dengue outbreak schoolchildren were given a note asking their parents to remove mosquito breeding sites around the home. "Soper... would have cleaned up this entire island of fewer than 200 square kilometers within a few months," he lamented.

That's why in 2010, he co-founded another company, Soper Strategies, which seeks to combine his hero's approaches with modern technology to rid islands or entire countries of their mosquito populations in "meticulously planned elimination campaigns, executed with military precision and discipline," as the website puts it. Candidate countries include Cape Verde, South Africa, and Saudi Arabia. Knols hoped to use Aruba to show that elimination Soper-style can work, but failed to secure the funding. Other clients have yet to come forward.

Knols believes it's just a matter of time. In his book, he even wondered whether "one day soon, a new Soper will stand up." It seemed clear who he had in mind.