New mosquito control methods pit the pests against themselves in Clovis

Listening to the humming noise made Jodi Holeman relax.

The sound meant the cardboard tube held to her ear contained a healthy batch of male mosquitoes thrumming their wings in confinement.

The previous week, a container of mosquitoes, shipped overnight from Kentucky, had not been as lively.

Holeman, scientific technical service director at the Consolidated Mosquito Abatement District, needed this bunch of about 1,000 males to be vital and virile for the job they had been sent to do: Mate with female mosquitoes in a neighborhood southeast of Clovis High School.

The male mosquitoes had been dusted with an insecticide that is harmless to them and their mates, but a pairing with females should produce baby mosquitoes that wither and never develop into mature, biting pests.

As strange as it sounds, Holeman said: “We’re turning mosquitoes into mosquito-control workers.”

The novel experiment, appropriately called the ADAM Project, is only the beginning of new strategies the district is looking at in its fight to control mosquitoes.

There’s an urgency to innovate.

Southeast Clovis has been plagued for the past three years with Aedes aegypti, a mosquito that Consolidated manager Steve Mulligan calls the “rat of the mosquito world” for its affinity for living in urban areas. The mosquito, a voracious day-time biter, can carry devastating diseases – dengue, yellow fever and chikungunya. A tropical-loving pest, it shouldn’t have survived in the central San Joaquin Valley’s dry summers and cold winters. But its numbers are growing. Eradication has been a priority, but traditional control efforts have fallen short.

The district now is counting on the insect’s libido to help in its ongoing fight to control the invasive species.

The army of male mosquitoes Holeman released on Aug. 21 was part of about 50,000 set aloft in batches between July 29 and Aug. 28. (Males don’t bite people; only the females suck blood to nourish babies.) Clovis residents welcomed the guys.

“Anything that can help alleviate the problem, I’m all for it,” said Kristen Starkweather, who greeted Holeman when she saw the Consolidated truck parked by her home. “I’m tired of being bitten.”

Disease breeds innovation

Everything pointed to the need for a new control approach.

The adult Aedes aegypti, commonly called the yellow fever mosquito, is becoming resistant to insecticides that can safely be used and are approved in California. The mosquito also is becoming difficult to locate, breeding in elusive spots. It needs only a couple of teaspoons of water to breed and within about a week, its babies can mature.

Mulligan had been keeping an ear cocked for control options, and at an American Mosquito Control Association meeting this year, he learned about adult male mosquitoes being used against the Asian Tiger mosquito (Aedes albopictus), which has become invasive in Southern California.

The results of the mosquito trial were promising. The Asian tiger mosquito, like the yellow fever mosquito, is a day-biter and urban dweller, which could bode well for the control strategy to work in Clovis.

The Asian tiger trial is a collaboration between the University of Kentucky and MosquitoMate Inc., a Kentucky-based biotechnology company. For the trial, adult males were dusted with the insecticide pyriproxyfen in an amount small enough not to harm the males nor their female mates, but strong enough to leave enough poison in breeding water to disrupt the development of mosquito larvae.

Mulligan saw potential benefit for using yellow fever males to carry insecticide to hidden egg-breeding nests. “The mosquitoes are better at finding the water sources than we are,” he said.

The University of Kentucky and MosquitoMate were willing to help Consolidated with a trial. They agreed to raise batches of Aedes aegypti mosquitoes, separate the males, dust them with the insecticide and ship them to Clovis.

Consolidated had to provide a starter group of mosquitoes before they could begin mass breeding, and would have to disseminate the mosquitoes and document the results.

The district turned to Anthony Cornel, an associate professor in the Department of Entomology at the University of California at Davis. Cornel works at the university’s Mosquito Control Research Laboratory outside Parlier and has cages where he raises mosquitoes for study.

Cornel sent off a batch of Aedes aegypti reared from eggs collected in Clovis.

“Very quickly, we had thousands and thousands of mosquitoes we could send back to them, dusted and with the females removed,” said Stephen Dobson, professor of entomology at the University of Kentucky and president of MosquitoMate.

Results are promising

Each week that Consolidated workers released dusted male mosquitoes they placed small cups of water nearby. The following week, they returned to collect water samples from the cups.

Cornel conducted assays of the water to see if enough insecticide had been deposited by the mosquitoes to kill larvae.

On a counter in the Parlier lab, he has rows of Petri dishes containing water from cups collected at the Clovis mosquito release sites. He’s added larvae that hopefully never mature past pupa, equivalent to the teenage stage between baby and adult mosquito.

“Two weeks ago, we saw really good activity, a lot of the water we brought back resulted in death,” Cornel said. “Last week’s water, we didn’t see much death, so we’re not sure why.”

Cornel has theories about what could have caused the bad week: The male mosquitoes were not healthy and frisky, possibly from exposure to heat in travel from Kentucky to Fresno.

“The males released likely didn’t mate as well with the wild females as they should have, he said. “We noticed a lot were dead and they looked like they were stressed … they were just not vibrant for them to perform very well out there in the field.”

It all bears further study into the behavior of the male mosquitoes, which would require following the mosquitoes in the field. Impossible? Not quite, but it wouldn’t be easy, Cornel said. “You can dust with a fluorescent dye and track where they fly.”

The effort would be worthwhile, he said. “We certainly don’t want to scrap (the ADAM Project) right now because it showed some promise, but why it didn’t consistently show promise we need to investigate.”

New studies on horizon

Cornel has a gift when it comes to identifying mosquitoes.

He’s one of a handful of entomologists in the world who can differentiate African mosquitoes and is an expert at looking at mosquito chromosomes.

Much of his study involves mosquitoes that transmit malaria to people. He’s part of a vector genetics lab of researchers who are using cutting-edge technology to investigate how malaria-transmitting mosquitoes are adapting to changing environments in Africa and Brazil.

Cornel has plans to also investigate the reason why Aedes aegypti is adapting to drier summer conditions and colder winters, such as in Clovis.

Of particular concern is the potential for the Aedes egypti to spread disease. So far no one has been infected by a mosquito in the Valley, but Fresno County’s health officer warned residents in June to be on alert to mosquito bites after the first case of chikungunya virus was diagnosed in a woman who was bitten while on vacation in another country. Chikungunya does not result in death, but the symptoms can be severe and disabling.

Cornel said chikungunya has become epidemic in Mexico, with 7,000 cases reported in the southern state of Guerrero since January. Someone could bring the virus back to Clovis and infect a mosquito that could pass the disease to local residents.

He is involved in a proposed project that could reduce the risk of dengue from Valley mosquitoes. Dengue has no vaccine and can be deadly.

The dengue research would use mosquitoes to fight themselves. In this case, researchers would introduce Wolbachia, a bacterium-like organism, into the male Aedes egypti. The male would infect a female mosquito, and the organism would interfere with the female’s immune system.

The female would see dengue as a foreign substance to be killed. An infected female mosquito “will not transmit dengue,” Cornel said.

Trials using Wolbachia are underway in Australia, Cornel said. Before research can begin in the Valley, though, the team needs federal and state approval. He expects to get that this year for studies to begin in 2016.

The University of Kentucky is a partner in the project and Consolidated would be a part of the control effort, Cornel said.

The district’s involvement will be essential and the ADAM Project has shown its commitment to mosquito control, Cornel said. “The district has essentially put two to three full-time staff available to do the study and to do it properly.”

Consolidated had hoped it could control the mosquito by spraying and by the public’s cooperation in eliminating any standing water, no matter how small the containers. Mulligan also had thought the drought would reduce mosquito numbers.

Aedes egypti, however, continued to multiply this summer and that required the collaboration with the UC Davis Mosquito Control Research Laboratory and the Kentucky research team.

“We’re not set up to do just research, but we need to do that so we can stay on the cutting edge,” Mulligan said. “Mosquitoes are evolving and adapting and becoming resistant to insecticides. We need novel techniques so we can stay ahead of them.”

This story was originally published September 6, 2015 at 8:00 AM with the headline "New mosquito control methods pit the pests against themselves in Clovis."