Mosquito Surveillance and Disease Monitoring
Success in mosquito control necessarily hinges upon accurate and timely surveillance information, reflecting the local abundances of different mosquito species in a variety of habitats. The effectiveness of a mosquito abatement program relies heavily on the knowledge of local breeding sources and the timing of adult mosquito hatches. Awareness of these sources and their characteristics allows TCWP to target larval mosquitoes at the appropriate time of season for the most effective control as well as to prepare for controlling adult mosquitoes. This system of surveying and cataloging larval and adult mosquito populations facilitates understanding of mosquito production, evaluation of the success of various control techniques, and makes possible a cost-effective review of the personnel and resources required for each task.
Larval Surveillance: Teton County is home to 39 species of mosquitoes that occupy diverse aquatic environments including flood-irrigated pasture and hayfields, seasonal snowmelt pools and naturally flooded stream banks and marshes. Teton County Weed & Pest personnel survey thousands of sites each year for larval mosquito activity. Beginning in March, when early season mosquito larvae hatch (often under the cover of ice) and continuing into October, mosquito control workers visit known and suspected mosquito breeding habitats to collect information and take control measures, when necessary. At each site, small samples of water are collected with a simple, standardized sampling tool familiarly known as a “dipper”. The amount of mosquitoes per dip is averaged and the habitat is described for future indexing. In characterizing each site, mosquito control workers record such information as water temperature, substrate characteristics, vegetation type and abundance as well as the amount of light and shade. Sample larvae from a site are returned to the TCWP laboratory where they are identified and recorded with the completed site survey into a GIS mapping program. Knowing when and where each species of mosquitoes is emerging allows us to more accurately predict future hatches and target similar environments where mosquito breeding is suspected.
Adult surveillance: In addition to larval surveillance, TCWP maintains a network of mosquito traps, which give us an indication of the relative abundance of the different mosquito species occurring throughout Teton County. Adult mosquitoes are identified to species and knowledge of the bionomics of the species involved then guides future larvicide treatments. Also, when surveys for adult mosquitoes indicate a large enough population, control using adulticide sprays may be warranted, if conditions permit.
TCMA employs two different types of adult mosquito traps:
Centers for Disease Control (CDC) CO2-baited Light Traps: These highly portable traps rely on a small incandescent light and a plume of CO2 provided by sublimating dry ice to lure host-seeking mosquitoes. They can be very effective collecting host-seeking mosquitoes at any time during the day but they require attention for their maintenance.
Mosquito Magnets: Mosquito Magnets also use a CO2 plume to attract mosquitoes, but because they use liquid propane tanks as a CO2 supply, they require less maintenance. They however have limited portability due to their larger size.
Disease monitoring: One of the most critical surveillance projects is the monitoring of field-collected adult mosquitoes for mosquito-borne viruses. We routinely test samples collected for adult mosquito surveillance for West Nile virus. Presently, we monitor for viral activity using the Rapid Analyte Measurement Platform (RAMP) system, which uses a qualitative immunochromatography assay to detect WNV. In disease monitoring, our attention is focused on those species of mosquitoes (Culex tarsalis)that most commonly transmit WNV between the primary disease reservoirs as well as those associated with bridging transmission to humans, such as Aedes vexans.