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LSU AgCenter mosquito researchers seek double whammy

It's not unusual in mid-summer to see Louisiana rice farmers crisscrossing their fields making test sweeps with large nets designed to capture and count adult stink bugs — a mid- to late-season threat to rice plants.

If the stink bug counts are high enough, farmers will apply a pesticide to protect the rice crop. Two familiar choices are the chemical sprays Karate and Mustang Max.

This year, LSU AgCenter insect experts are running a series of experiments in southwestern Louisiana rice fields to gauge whether treatments for stink bugs could be tweaked a bit to also kill medically threatening mosquitoes breeding in rice fields.

“There may be a way of tweaking the volume or timing of pesticide applications against stink bugs to control two (insects) for the price of one,” said Michael Stout, an LSU AgCenter entomologist working with LSU AgCenter mosquito expert Michael Perich on the study.

“There may be a way of doing a double whammy,” Stout said.

Perich and Stout plan to apply to the Louisiana Board of Regents this fall for a six-figure research grant to study what impact various chemicals used to control stink bugs might have on mosquitoes in the same rice fields.

“We feel like the timing is pretty good to ask for the grant,” Stout said. “We have some new chemicals on the market to control rice stink bugs, and there are new mosquito-borne diseases (primarily the West Nile virus) to deal with.”

Treatments likely to be tested at varying dosages for their impact on mosquito populations include methyl parathion, Karate, Mustang Max and malathion. Aerial applications at low and ultra-low volumes are likely to be used, said Perich, adding that the grant application hasn't been written yet.

A decision on whether the LSU AgCenter wins the grant money likely won't come before next spring.

Rice fields generally aren't considered a major threat for spreading West Nile virus, but Perich and Stout's research could have international implications. Mosquitoes typically found in rice fields can spread malaria and other diseases that remain big problems in developing countries.

The two mosquitoes typically found in Louisiana rice fields, the Anopheles quadrimaculatus and Psorophora columbiae, are considered secondary or minor vectors of West Nile virus. Southern House mosquitoes and Asian Tiger mosquitoes, both of which breed in urban areas, are considered the top threats to spread West Nile to humans.

Louisiana continues to grapple with the potentially deadly West Nile virus, which first appeared in New York in 1999 and has since spread to at least 44 states. So far this year, at least 34 cases of West Nile have surfaced in Louisiana. In 2002, there were 329 confirmed West Nile cases in Louisiana and 24 deaths.

Nationally, West Nile had killed at least 17 people as of Aug. 26, with eight of those deaths in hard-hit Colorado. No deaths have been reported in Louisiana so far in 2003, although health officials remain wary.

Ana Maria Sanchez is an LSU entomology Ph.D. candidate working with Stout and Perich to gauge the number of mosquitoes and the various types of larvae and adults found in rice fields. She has set up several test plots at the 1,000-acre LSU AgCenter Rice Research Station near Crowley as part of the study.

A recent weekday found Sanchez dipping a test instrument in flooded rice fields at the LSU AgCenter research station to count mosquito larvae. Numbers were relatively low in early August, but Sanchez and Perich expect the counts to increase.

Sanchez said the research could help fight mosquito-borne diseases in her native Peru, where she attended undergraduate school. She later earned a master's degree from the London School of Tropical Medicine and Hygiene.

“One of the mosquitoes typically found in rice fields carries malaria, and in northern Peru, our rice-growing region, many people get malaria,” Sanchez said.

Perich said the plan over the next 18 months is to make detailed mosquito counts in rice fields, identify the types of mosquitoes found and estimate how many larvae grow to adulthood in rice ponds. Light traps and other devices will be used to catch adult mosquitoes and to monitor the growth of larvae.

Related research will gauge how pesticide applications designed to control stink bugs affect the mosquito populations. Sentinel cages stocked with mosquitoes could be placed at varying heights in rice fields to gauge how many of the blood-sucking insects are killed when stink bug sprays are applied at different volumes, Perich said.

“It's an important time to be doing this research because of all the public health implications,” Perich added.

Randy McClain (225-578-2263 or writes for the LSU AgCenter.

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