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The battle against Aedes aegypti, the mosquito that spreads Zika

Aedes aegypti mosquito.
The UC Mosquito Research Laboratory in Parlier is the epicenter of California research on the Aedes aegypti mosquito, a tiny, black and white mosquito that can spread the Zika virus.

Aedes aegypti were first identified in California in June 2013, when they were found in the San Joaquin Valley communities of Clovis and Madera. They have now been detected in certain Fresno County neighborhoods, plus the Bay Area, and Southern California, according to the California Department of Public Health.

To date, the Zika virus hasn't been found in the California mosquitoes, however with thousands of Americans traveling to Brazil for the 2016 Olympics, plus travelers regularly visiting other countries with outbreaks of Zika, some could be carriers of the virus when they come home.

The UC Mosquito Research Laboratory, located at the 300-acre UC Kearney Agricultural Research and Extension Center, is led by entomologist Anthony Cornel, Ph.D. He is working with the Consolidated Mosquito Abatement District (CMAD) on research projects aimed at controlling this new mosquito menace.

“When Aedes aegypti first came to the United States a few hundred years ago, there were major epidemics of yellow fever in the East and South,” Cornel said. “Today this mosquito serves as the vector of three other serious viruses, dengue, Chikungunya and Zika, which are major threats to global public health.”

What keeps him up at night, Cornel said, is grave concern that there will be a Zika outbreak in California.

“Right now, our only control tool in response to a disease outbreak is use of insecticides,” Cornel said. “If Zika breaks out here, we will have to do whatever we can to reduce the number of adult Aedes aegypti mosquitoes right away, and a single insecticide application isn't going to do it.”

Anthony Cornel, Ph.D., UC Davis entomologist and UC ANR researcher, based at the UC Kearney Agricultural Research and Extension Center in Parlier.

The Cornel lab at Kearney and the Consolidated Mosquito Abatement District are conducting myriad laboratory and field research trials to evaluate insecticide treatment options, to minimize potential mosquito breeding sites, and to understand Aedes aegypti biology and behavior in order to inform control decisions should such an outbreak occur. Following are summaries of research underway that involves the UC Mosquito Research Laboratory in the fight against the Zika vector Aedes aegypti.

Make female mosquitoes infertile

Working in cooperation with scientists at the University of Kentucky and MosquitoMate Inc., Cornel and CMAD staff are releasing male mosquitoes that have been infected with a bacterium, Wolbachia pipientis. When these males mate with local females, the females pick up Wolbachia, which causes them to lay eggs that will not hatch.

“The infected male mosquitoes are shipped to us from Kentucky overnight twice a week and we release them in the test area in Clovis,” Cornel said. “These male mosquitoes are harmless to humans. They do not bite and can't transmit disease.”

Special traps have been placed in the treatment area and in a nearby control area, where no Wolbachia-infected mosquitoes are released.

“Right now, the number of eggs we are getting is very much reduced in the treated site,” Cornel said.

A colony of Aedes agypti mosquitoes that originated in Clovis, Calif.

Pesticide applications and mosquito resistance

Mosquitoes are generally susceptible to the lethal effects of insecticides.

“In mosquito control, we use insecticide concentrations much lower than is typically used for controlling other pests that hamper agricultural operations,” Cornel said.

But Aedes aegypti appear to quickly develop insecticide resistance. In laboratory and field research, Cornel is studying Aedes aegypti's uncanny ability to survive certain insecticide treatments.

Cornel maintains colonies of Aedes aegypti in the lab that are susceptible to insecticides. “These are colonies that have been with us for many years,” he said.

For comparison, the scientists have collected mosquitoes that are living in local neighborhoods. Mosquitoes representing different colonies are dropped inside glass bottles that are coated inside with insecticides. The scientists record how many of the mosquitoes are knocked down and how many die.

The experiments have shown that mosquitoes collected locally are resistant to almost all pyrethroid insecticides except one, Deltamethrin, which is not registered for mosquito control in California. However, these mosquitoes are also susceptible to organophosphate insecticides.

“Deltamethrin is used effectively in the European Union and other countries, but unfortunately, it is not yet available for use here,” Cornel said. “The company that makes the product is working to get California Department of Pesticide Regulation approval for using it in the state.”

The Cornel lab has also studied various insecticides in field applications.

“We placed susceptible and local mosquitoes in sentinel cages in a field and sprayed them from a truck 100-, 200- and 300-feet away in an open field situation,” Cornel said. “We recorded knockdown and mortality one hour and 24 hours after application.”

The field studies verified what the scientists found in their lab tests: local Aedes aegypti have developed resistance to most pyrethroids, but organophosphate insecticides offer effective control. However, the study doesn't prove what will happen in residential areas.

“We were in an open field, with no trees and houses to block the spread of the chemical,” Cornel said. “Now we should evaluate the efficacy of ultra-low-volume applications of malathion, an organophosphate, in a residential area.”

Underground drains that channel irrigation and rain runoff from backyards to the front are suspected Aedes aegypti breeding areas.

Reduce mosquito breeding

A well-known approach to reducing mosquito populations is elimination of standing water where mosquitoes can breed. Bird baths, abandoned toys, old tires and drainage plates under potted plants are all potential receptacles for standing water and should be discarded or kept dry. Less obvious are underground yard drains often found in newer housing developments. The scientists believe that the drains, designed to channel rain or irrigation runoff to the gutter in front of the house, may leave a perpetual supply of standing water in the buried pipe beneath the soil surface, which provide sites for mosquito development.

To test the theory, the CMAD personnel went door to door in a Clovis neighborhood to work with residents to eliminate water sources and to place fine netting on the ends of the drainage pipes.

“We have 80 percent compliance in the testing area,” Cornel said. “A few people have refused, which surprised me. But most of the residents were willing to help.”

The district is monitoring mosquito traps placed in the test area and in another Clovis neighborhood where yard drains haven't been netted.

“We have no results yet. When the study is done, CMAD will give me the data and I will analyze it,” Cornel said. “If I do see a statistically significant impact on mosquito populations, then that will confirm our suspicions and give us more convincing information to share in communities with Aedes aegypti to get them to eliminate even unseen potential mosquito breeding sites.”

If the yard drains are a confirmed mosquito breeding location, it may require a redesign to make sure that they do not hold water.

Aedes aegypti mosquito larvae incubating in a tray at the UC Mosquito Research Laboratory, on the grounds of the UC Kearney Agricultural Research and Extension Center in Parlier.


Scientists have sequenced the genome of Aedes aegypti and are using genetics to understand the movement of the pest in California.

“We want to know if the population in California comes from multiple introductions, or from a single introduction that has subsequently spread,” Cornel said.

This research is being done in collaboration with Gregory Lanzaro, Ph.D., and Yoosook Lee, Ph.D., in the Department of Pathology, Microbiology and Immunology at UC Davis, and has not yet been published, but preliminary results show that the population of Aedes aegypti that is south of the Tehachapi Mountains is probably from a separate introduction than the one that settled in Fresno, Clovis and Madera.

The scientists are also using genetics to determine the mosquitoes' dispersal patterns.

“We need to know this to help us develop effective control strategies,” Cornel said. “For example, if we've located an area with a large number of mosquitoes, we need to know how large an area we have to treat.”

The general consensus from studies around the world is that these mosquitoes don't fly very far from their development site.

“We're finding much the same here, usually no more than 80 meters,” he said. “Except, there are always a few males that disperse long distances within 24 hours – sometimes over 300 meters in one night.”

UC ANR entomologist Anthony Cornel, left, and U.S. Congressman Jim Costa watch as male mosquitoes infected with Wolbachia pipientis are released in a Clovis neighborhood on Aug. 16, 2016. Costa is calling on Congress to provide funding for Aedes aegypti research and control.
Posted on Monday, August 22, 2016 at 11:05 AM
Tags: Aedes Aegypti (33), Anton Cornel (5), mosquitoes (32), Zika (3)

Officials target mosquitos that spread zika with new tools

Aedes aegypti mosquitoes are found in several Fresno County neighborhoods. They are the target of novel control efforts.
UC entomologist Anton Cornel, based at the UC Kearney Agricultural Research and Extension Center, is working with the Consolidated Mosquito Abatement District in Fresno County to battle Aedes aegypti mosquitos, the species that can spread zika, chikungunya, dengue and yellow fever viruses, reported Barbara Anderson in the Fresno Bee.  

(While populations of aedes aegypti have been found in California, the diseases have not.)

Cornel said officials need to attack the mosquitos on several fronts.

“There is no silver bullet,” he said.

One of the novel methods the scientists are studying is releasing male mosquitos infected with Wolbachia, a bacterium-like organism. They transfer the infection to females when they mate. The females then produce eggs that do not hatch.

Cornel is hopeful about the new technique.

"Maybe this proves to be an effective strategy, and hopefully it might become a standard control method," he said.

The Fresno Bee story also outlined a more-traditional approach to reducing mosquito populations that will be implemented by the Consolidated Mosquito Abatement staff. In one subdivision in southeast Clovis, the mosquito district asked residents for permission to enter their yards to search for and destroy mosquito breeding spots, such as old tires, toys, pet dishes and underground backyard drains. The project will show whether a vigilant effort to remove standing water will significantly reduce the number of mosquitos found in the neighborhood.

Posted on Monday, June 13, 2016 at 1:42 PM
Tags: aedes agypti (1), Anton Cornel (5), mosquitos (2), zika (3)

UC fights a mosquito new to California

Aedes aegypti mosquito perched on a scientist's finger. (Photo: Jodi Holeman, Consolidated Mosquito Abatement District.)
UC researcher Anton Cornel, based at the UC Kearney Agricultural Research and Extension Center in Parlier and affiliated with UC Davis, is conducting research aimed at eradicating Aedes Agypti mosquitos, a type of mosquito that is new to the state of California, reported Sasha Khokha on The California Report.

The mosquitos - which can transmit dengue fever, yellow fever and chikungunya - were found in Clovis, Madera and San Mateo last year. Cornel has deployed 146 traps provided by the Centers for Disease Control in a Clovis neighborhood to see if they will knock down the population of the unwelcome pest.

Unlike more sophisticated traps that cost hundreds of dollars, the traps being used in Clovis are handmade in Puerto Rico for about $6 each, Khokha reported.

"(Mosquitos) are attracted to this trap to lay their eggs in, they get stuck to the glue, and of course, that's the end of the mosquito," Cornel said.

Listen to the story on The California Report by clicking the link below:

Posted on Thursday, August 7, 2014 at 9:50 AM
Tags: Anton Cornel (5), mosquitos (2)

'Great Day' morning program features UC Kearney Ag REC

The popular morning television program "Great Day," which airs daily on KMPH Channel 26 in Fresno, featured the work of scientists at the UC Kearney Agricultural Research and Extension Center in six live segments during the five-hour program this morning.

Reporter Clayton Clark and photographer Ryan Hudgins arrived at the Kearney greenhouse at 4:30 a.m. to interview the scientists helping California farmers feed the nation and world sustainably.

See clips of the interviews in the one-minute video below:

Segments included:

  • An overview of research and extension activities at Kearney by director Jeff Dahlberg.

  • UC blueberry and blackberry research that has made these commodities important crops in the San Joaquin Valley with Manuel Jimenez, UC Cooperative Extension farm advisor in Tulare County.

  • Beneficial insects, pests and invasive species that are part of research by Kent Daane, UCCE specialist in the Department of Environmental Science and Policy Management at UC Berkeley. Daane shared a handful of leaf-footed bugs with the reporter.

  • How global information systems are changing the way farmers and researchers are looking at farmings systems with Kris Lynn-Patterson, coordinator of the GIS program at Kearney.

  • Just like people, plants get sick. UC plant pathologist Themis Michailides explained research efforts to cure plant diseases.

  • Uncommon wine varieties that might lead to new fine wines ideally suited to be produced in the Valley's warm climate, with Matt Fidelibus, UCCE specialist in the Department of Viticulture and Enology at UC Davis.

  • The very real threat of West Nile virus in mosquitoes in the valley, with medical entomologist Anton Cornel.
Posted on Wednesday, May 22, 2013 at 12:13 PM

The Mosquito Researchers

It was a major milestone, sequencing the genome of Culex quinquefasciatus, the so-called “southern house mosquito.” The research, spearheaded by UC...

Anton Cornel
Anton Cornel

MOSQUITO RESEARCHER Anthony "Anton" Cornel of UC Davis collected and established the colony of Culex quinquefasciatus mosquitoes that was sequenced. Here he's shown working in a field tent identifying mosquitoes in Cameroon. (Photo by Kevin N'Gabo)

Mosquito Researchers
Mosquito Researchers

MOSQUITO RESEARCHERS Anton Cornel (front) and Gregory Lanzaro aboard a ferry on Lake Victoria, Kenya, in June of this year. They do research in Africa on malaria mosquitoes. (Photo by Stephen Mulligan)

Posted on Thursday, October 7, 2010 at 6:08 PM

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