Intensive early season adulticide applications decrease arbovirus transmission throughout the Coachella Valley,...

Area of Science:

• Veterinary Public Health
• Medical Entomology
• Arbovirology

Background:

• The Salton Sea shoreline in Coachella Valley is a consistent focus for the seasonal onset of St. Louis encephalitis virus (SLEV), western equine encephalomyelitis virus (WEEV), and West Nile virus (WNV).
• Initial amplification in the Culex tarsalis/wild bird cycle at this focus is linked to subsequent virus dispersal throughout southern California.

Purpose of the Study:

• To evaluate the effectiveness of ultra-low volume (ULV) insecticide applications in interrupting West Nile virus (WNV) amplification and dispersal.
• To assess the impact of different application timings and methods on mosquito populations and WNV transmission.

Main Methods:

• Ground ULV applications of Pyrenone 25-5 were initiated in 2004, one month after initial WNV detection.
• In 2005, ground and aerial ULV applications were evaluated in May and June following WNV detection.
• In 2006, aerial ULV applications commenced immediately after the first virus detection in mid-April.

Main Results:

• In 2004, localized treatments had little effect, and WNV spread throughout the valley, resulting in human cases.
• In 2005, ground (43% mortality) and aerial (34% mortality) applications showed variable mosquito kill and limited control.
• In 2006, immediate aerial ULV applications reduced Cx. tarsalis abundance, delayed WNV activity, and decreased Cx. quinquefasciatus transmission, with no human cases reported.

Conclusions:

• Early and immediate aerial ULV applications are more effective in controlling WNV amplification and dispersal than delayed or ground-based treatments.
• Integrated mosquito management strategies, including timely insecticide applications, are crucial for preventing WNV outbreaks and protecting public health.