Traditionally the driest month of the year in South Louisiana, October was wetter and warmer than the ten-year historical average for both parameters. Total rainfall during October (6.07 in) was markedly higher than the ten-year historical average (1.89 in) for the month. The continued temperature and rainfall of late summer has produced a few nuisance mosquito species in abundance. In particular, the extended warm period has produced an outbreak of Mansonia spp., which produce one generation per year and are associated with floating vegetation such as water hyacinth. The Madisonville and Mandeville areas were particularly plagued by Mansonia spp. mosquitoes during the week prior to the Halloween holiday.
Additionally, Culex nigripalpus and Cx. salinarius mosquitoes, both secondary WNV vectors that began to show up in September, have continued to dominate trap collections in October. Given the continued production of nuisance and vector species, STPMAD control efforts operated at moderate levels during the month of October. The Twin Otter flew ten missions in October providing service to 204,625 acres. Night ultra-low volume (ULV) spray trucks sprayed an additional 187,733 acres (up 41.5% from 132,654 acres during September) in 209 separate missions during October.
Of the 66 West Nile virus (WNV)-infected mosquitoes pools collected this year, only one was collected in the month of October (down from two in September). Pooled samples of mosquitoes are tested weekly by the Louisiana Animal Disease Diagnostic Laboratory (LADDL), at the LSU School of Veterinary Medicine. One of the 746 (0.01%) total pools of mosquitoes tested positive for WNV infection in October. The WNV-infected mosquito pool was collected in Abita Springs. Mosquito traps set over 241 trap nights, at various locations across St. Tammany Parish, collected 181,624 mosquitoes (up from 214,136 in September) or 753.6 mosquitoes/trap night (down 31% from 1,092.5 /trap night in September).
Though the WNV risk may be slight, we still recommend taking all precautions to avoid mosquito bites including: wearing mosquito repellents that contain DEET, Picaridin, or oil of lemon eucalyptus, avoiding peak biting times, and wearing long sleeves and pants can reduce your personal risk.
Kevin A. Caillouet, Ph.D., M.S.P.H.