Rice Farming

As the West Nile virus moved westward last year, leaving fear in its path, some outside of agriculture accused the rice industry of providing more than 3 million acres of mosquito-breeding ponds.

Although rice fields do provide habitat for some mosquito species that could possibly spread West Nile virus in Southern states, insect experts in California say they are more concerned about the species that prefer standing water and are found in urban areas. Those are the ones, they say, that do spread the sometimes-deadly disease.

“Anything that will reduce container-breeders is really what we are after,” says Max Meisch, a University of Arkansas entomology professor in Fayetteville. “What I think we want to emphasize is the mosquitoes that breed in rice fields, up to this point, are not really significantly contributing to West Nile. The potential is there, but if you want to get down to it, the mosquitoes that are going to cause those diseases are urban mosquitoes.”

Michael Perich, a Louisiana State University medical entomologist in Baton Rouge, agrees and says growers and local mosquito districts should communicate with their urban neighbors.

“Public education goes a long way, and it also gets them on your side and keeps them informed,” says Perich, who’s with the LSU AgCenter.

On the West Coast, preliminary studies suggest that mosquitoes found in rice fields may be of more importance in transmitting the virus than in other areas of the country.

Rice fields harbor mosquito immature stages, larvae and pupae, and entomologists recommend growers follow cultural practices to help reduce mosquito habitat. But they say they also realize that rice growers place a priority on their crop and are limited in what they can actually do to control the insect pest.

Insect experts also are studying how rice-related cultural practices, such as sprays applied to fight rice stink bug or rice water weevil, may affect mosquito populations.

What is West Nile virus?
First identified in Africa in 1937, the sometimes-deadly disease first appeared in the United States in New York City in 1999. It has since moved westward and has been found in every rice-producing state, according to the Centers for Disease Control and Prevention.

The CDC has noted only one case of West Nile in California. The female victim worked at FedEx near Los Angeles International Airport, and experts theorize an infected mosquito that hitchhiked in from an area where West Nile is endemic bit her.

So far, West Nile virus has infected 4,007 humans and killed 263, according to the CDC. The disease is particularly hard on horses, killing about 30 percent of animals that are infected.

West Nile is caused by a virus closely related to other organisms that causes St. Louis encephalitis. Both diseases involve swelling of the brain.

Mosquitoes pick up the virus after feeding on West-Nile-infected birds. When they bite a human or other mammal, they transmit the virus.

The disease normally cannot be spread directly from human to human, except when somebody receives blood or a transplant organ from an individual who has West Nile virus. The most transmission route involves an avian or bird reservoir as an intermediary between mosquitoes and humans.

Although more than 135 bird species can become infected with West Nile, the family that includes crows, blue jays, magpies and ravens appears to be most commonly infected and killed, according to the CDC. Humans and horses are what disease experts refer to as “incidental hosts” or “dead-end hosts.”

Because the disease needs an avian host, disease experts examine dead birds to see if the virus is present. They also monitor West Nile’s spread by putting out flocks of sentinel chickens near high-risk areas and routinely drawing blood to see if the birds have been infected.

David Brown, who heads the Sacramento-Yolo Mosquito and Vector Control District, says he expects the disease to show up in California this season because it’s already been found in Washington state. In reviewing how the disease spread elsewhere, Brown says it tends to follow major migratory bird routes, and California is within the Pacific Flyway.

Southern mosquitos
The CDC considers mosquitoes in the Culex genus to be the primary West Nile vectors. In Louisiana, Culex quinquefasciatus, or Southern house mosquito, falls into that category, Perich says. It prefers drainage ditches to rice fields, particularly if the waterways are high in organic waste or vegetative matter.

Shady, overgrown areas provide resting and hiding places for adults. By keeping weeds down, you’re also permitting more sun exposure, which is the No. 1 killer of mosquito larvae.

Anopheles crucians is another vector found both in rice fields and shaded swamps. Although the species is a potential malaria vector in the state, it has not been known to vector West Nile virus, Perich says.

One of the main rice-field mosquitoes is Psorophora columbiae, but scientists are unsure whether this species can spread West Nile virus in the wild.

Flushing rice fields helps reduce some mosquito species, such as Anopholes and Culex, while it enhances habitat for Psorophora and Ochlerotatus, Perich says.

In Arkansas, Culex salinarius is a proven West Nile vector, and Anopheles quadrimaculatus is a strong suspect.

The CDC has included all of the above species on a list of 36 mosquito species found in West Nile positive mosquito pools since 1999.

California vectors
Of the 50 or so mosquito species that inhabit California, only a handful frequent rice fields. Anopheles freeborni, otherwise known as the western malaria mosquito, develops in clean, clear, shady, cool water, such as that found in rice fields.

As soon as temperatures hit the 60s in late winter, A. freeborni emerges. Although the species feeds aggressively on mammals, it avoids birds. Because of that, entomologists don’t consider it a vector of West Nile virus, says Brown, who also is president of the American Mosquito Control Association.

Culex tarsalis is the other species inhabiting California rice fields. Because it feeds on both mammals and birds, it can pick up West Nile virus as well as other related encephalitis diseases and transmit them to humans.

Locally waged mosquito wars
Most states in which rice is grown have organized county or regional mosquito abatement districts that fight the biting insects. Most use a combination of Bacillus thuringiensis israeli, a bacteria that attacks and kills only larval mosquitoes, and insect growth regulators that target larvae and pupae.

In California, some of the districts also plant mosquito fish in rice fields to help control the pests.

Researchers in Louisiana are examining how rice cultural practices may affect mosquito control. Karate, marketed as Warrior in California, also has activity on adult mosquitoes and is used by public health officials under the brand name, Demand.

What the researchers want to find out is how applications of Karate, pyrethroids and other insecticides affect mosquito predators as well as rice stink bugs and rice water weevil. In Louisiana, the studies will b3 conducted in both small plots as well as commercial fields.

Contact Vicky Boyd at (209) 571-0414 or vlboyd@att.net.

5 ways to put the bite on ‘skeeters’

1. Avoid seepage. The moist areas provide prime mosquito-breeding habitat.

2. Keep levees and checks free of weeds. A true monoculture reduces mosquito populations.

3. Check with the local mosquito abatement district before you spray for stink bugs or rice water weevils. The district may have put out mosquito fish (Gambusta affinis) that could be killed by insect-control products. Also coordinate water management with the district, so you’re not draining a field right after the fish have been planted.

4. Provide access to fields so mosquito control employees can conduct surveillance activities.

5. After harvest, avoid reflooding until Nov. 1 or as late as possible. This helps prevent mosquito populations from exploding late in the year.

Hotlink:

The Center for Disease Control and Prevention West Nile page: http://www.cdc.gov/ncidod/dvbid/westnile/index.htm

Help take the bite out of West Nile virus Work with local mosquito-control districts to reduce disease potential
By Marni Katz
As the West Nile virus moved westward last year, leaving fear in its path, some outside of agriculture accused the rice industry of providing more than 3 million acres of mosquito-breeding ponds. Although rice fields do provide habitat for some mosquito species that could possibly spread West Nile virus in Southern states, insect experts in California say they are more concerned about the species that prefer standing water and are found in urban areas. Those are the ones, they say, that do spread the sometimes-deadly disease. “Anything that will reduce container-breeders is really what we are after,” says Max Meisch, a University of Arkansas entomology professor in Fayetteville. “What I think we want to emphasize is the mosquitoes that breed in rice fields, up to this point, are not really significantly contributing to West Nile. The potential is there, but if you want to get down to it, the mosquitoes that are going to cause those diseases are urban mosquitoes.” Michael Perich, a Louisiana State University medical entomologist in Baton Rouge, agrees and says growers and local mosquito districts should communicate with their urban neighbors. “Public education goes a long way, and it also gets them on your side and keeps them informed,” says Perich, who’s with the LSU AgCenter. On the West Coast, preliminary studies suggest that mosquitoes found in rice fields may be of more importance in transmitting the virus than in other areas of the country. Rice fields harbor mosquito immature stages, larvae and pupae, and entomologists recommend growers follow cultural practices to help reduce mosquito habitat. But they say they also realize that rice growers place a priority on their crop and are limited in what they can actually do to control the insect pest. Insect experts also are studying how rice-related cultural practices, such as sprays applied to fight rice stink bug or rice water weevil, may affect mosquito populations. What is West Nile virus? First identified in Africa in 1937, the sometimes-deadly disease first appeared in the United States in New York City in 1999. It has since moved westward and has been found in every rice-producing state, according to the Centers for Disease Control and Prevention. The CDC has noted only one case of West Nile in California. The female victim worked at FedEx near Los Angeles International Airport, and experts theorize an infected mosquito that hitchhiked in from an area where West Nile is endemic bit her. So far, West Nile virus has infected 4,007 humans and killed 263, according to the CDC. The disease is particularly hard on horses, killing about 30 percent of animals that are infected. West Nile is caused by a virus closely related to other organisms that causes St. Louis encephalitis. Both diseases involve swelling of the brain. Mosquitoes pick up the virus after feeding on West-Nile-infected birds. When they bite a human or other mammal, they transmit the virus. The disease normally cannot be spread directly from human to human, except when somebody receives blood or a transplant organ from an individual who has West Nile virus. The most transmission route involves an avian or bird reservoir as an intermediary between mosquitoes and humans. Although more than 135 bird species can become infected with West Nile, the family that includes crows, blue jays, magpies and ravens appears to be most commonly infected and killed, according to the CDC. Humans and horses are what disease experts refer to as “incidental hosts” or “dead-end hosts.” Because the disease needs an avian host, disease experts examine dead birds to see if the virus is present. They also monitor West Nile’s spread by putting out flocks of sentinel chickens near high-risk areas and routinely drawing blood to see if the birds have been infected. David Brown, who heads the Sacramento-Yolo Mosquito and Vector Control District, says he expects the disease to show up in California this season because it’s already been found in Washington state. In reviewing how the disease spread elsewhere, Brown says it tends to follow major migratory bird routes, and California is within the Pacific Flyway. Southern mosquitos The CDC considers mosquitoes in the Culex genus to be the primary West Nile vectors. In Louisiana, Culex quinquefasciatus, or Southern house mosquito, falls into that category, Perich says. It prefers drainage ditches to rice fields, particularly if the waterways are high in organic waste or vegetative matter. Shady, overgrown areas provide resting and hiding places for adults. By keeping weeds down, you’re also permitting more sun exposure, which is the No. 1 killer of mosquito larvae. Anopheles crucians is another vector found both in rice fields and shaded swamps. Although the species is a potential malaria vector in the state, it has not been known to vector West Nile virus, Perich says. One of the main rice-field mosquitoes is Psorophora columbiae, but scientists are unsure whether this species can spread West Nile virus in the wild. Flushing rice fields helps reduce some mosquito species, such as Anopholes and Culex, while it enhances habitat for Psorophora and Ochlerotatus, Perich says. In Arkansas, Culex salinarius is a proven West Nile vector, and Anopheles quadrimaculatus is a strong suspect. The CDC has included all of the above species on a list of 36 mosquito species found in West Nile positive mosquito pools since 1999. California vectors Of the 50 or so mosquito species that inhabit California, only a handful frequent rice fields. Anopheles freeborni, otherwise known as the western malaria mosquito, develops in clean, clear, shady, cool water, such as that found in rice fields. As soon as temperatures hit the 60s in late winter, A. freeborni emerges. Although the species feeds aggressively on mammals, it avoids birds. Because of that, entomologists don’t consider it a vector of West Nile virus, says Brown, who also is president of the American Mosquito Control Association. Culex tarsalis is the other species inhabiting California rice fields. Because it feeds on both mammals and birds, it can pick up West Nile virus as well as other related encephalitis diseases and transmit them to humans. Locally waged mosquito wars Most states in which rice is grown have organized county or regional mosquito abatement districts that fight the biting insects. Most use a combination of Bacillus thuringiensis israeli, a bacteria that attacks and kills only larval mosquitoes, and insect growth regulators that target larvae and pupae. In California, some of the districts also plant mosquito fish in rice fields to help control the pests. Researchers in Louisiana are examining how rice cultural practices may affect mosquito control. Karate, marketed as Warrior in California, also has activity on adult mosquitoes and is used by public health officials under the brand name, Demand. What the researchers want to find out is how applications of Karate, pyrethroids and other insecticides affect mosquito predators as well as rice stink bugs and rice water weevil. In Louisiana, the studies will b3 conducted in both small plots as well as commercial fields. Contact Vicky Boyd at (209) 571-0414 or vlboyd@att.net. 5 ways to put the bite on ‘skeeters’ 1. Avoid seepage. The moist areas provide prime mosquito-breeding habitat. 2. Keep levees and checks free of weeds. A true monoculture reduces mosquito populations. 3. Check with the local mosquito abatement district before you spray for stink bugs or rice water weevils. The district may have put out mosquito fish (Gambusta affinis) that could be killed by insect-control products. Also coordinate water management with the district, so you’re not draining a field right after the fish have been planted. 4. Provide access to fields so mosquito control employees can conduct surveillance activities. 5. After harvest, avoid reflooding until Nov. 1 or as late as possible. This helps prevent mosquito populations from exploding late in the year. Hotlink: The Center for Disease Control and Prevention West Nile page: http://www.cdc.gov/ncidod/dvbid/westnile/index.htm
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