SDSU thresholds trigger mosquito spraying

SDSU thresholds trigger mosquito spraying A South Dakota State University specialist is once again advising that local governments follow thresholds based on SDSU research when deciding when to spray for adult mosquitoes.

South Dakota State University Extension Entomologist Mike Catangui developed the thresholds after studying data compiled by SDSU research parasitologist Mike Hildreth. Catangui also worked with Sioux Falls environmental health manager Dorothy Franklin in setting the thresholds.

The thresholds are based on Hildreth�s data tracking South Dakota mosquito populations. The data also reflect the effectiveness of different mosquito traps at capturing two species of mosquito known to transmit West Nile Virus in South Dakota, the western encephalitis mosquito (Culex tarsalis) and the inland floodwater mosquito (Aedes vexans). Culex tarsalis is the main vector of the disease, but Aedes vexans, the main nuisance mosquito in South Dakota, can also transmit it, Catangui said.

�For communities that have mosquito-control programs, these are some suggested guidelines to use as one consideration in deciding when to spray in your community,� Catangui said.

But he added that the guidelines are not absolutes, and that communities may have local conditions that may dictate different thresholds.

For the 2005 mosquito season that ends in October, Catangui recommends:

? For CO2-baited miniature light traps (CDC traps): Spray when traps show 10 Culex tarsalis or 100 Aedes vexans per trap per night, whichever comes first, on any two out of four consecutive trapping nights.

? For unbaited New Jersey light traps: Spray when traps show five Culex tarsalis or 50 Aedes vexans per trap per night, whichever comes first, on any two out of four consecutive trapping nights.

? For Mosquito Magnet (Defender or Liberty Models): Spray when traps catch 75 Culex tarsalis or 750 Aedes vexans per trap per night, whichever comes first, on any two out of four consecutive trapping nights.

Catangui added that ongoing data gathered by SDSU research parasitologist Mike Hildreth makes it clear that mosquito populations have peaked ahead of the human West Nile disease peak. That suggests that spraying, if it�s done when traps show that target mosquito species have surpassed low thresholds, should eliminate some of the human cases.

The mosquito spraying thresholds that Catangui are conservative by design in order to prevent disease transmission, and not merely to reduce nuisance biting.

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