Lab · Technology

Mosquito surveillance traps

Where it fits

• West Nile virus testing in urban Culex. CDC calls gravid traps useful for Culex pipiens and Cx. quinquefasciatus, especially in urban areas. Gravid females have already taken a blood meal, which makes it more likely the trap catches infected mosquitoes. California's plan notes gravid-trap catches may have a higher infection rate than CO2-trap catches, and the mosquitoes arrive alive for virus testing.
• A broad picture of the biting population. CDC light traps baited with dry ice catch a wide range of Aedes, Anopheles and Culex. CDC advises setting them at dusk, collecting after dawn, and hanging them about 5 feet off the ground. In New Orleans surveillance data they gave the highest species diversity of the three trap types and caught Culex salinarius and Aedes vexans more often than BG-Sentinel traps.
• Aedes aegypti and Ae. albopictus. CDC names BG-Sentinel traps and gravid traps such as the autocidal gravid ovitrap as the most commonly used adult traps for these species. BG-Sentinels collect females in all physiological states, and gravid traps are cheaper and easier to run. In Puerto Rico, local chikungunya transmission dropped significantly when Ae. aegypti fell below three females per sticky gravid trap per week.
• Cheap presence checks with ovitraps. CDC says a small number of ovitraps is usually enough to show the vector is present, and fewer than 100 can reliably estimate abundance in a large urban neighbourhood, usually one per city block. Traps must be serviced at least weekly, because an ovitrap left out longer can become a larval site and start producing adults.
• Turning counts into action. California compares adult Culex abundance with the five-year average for the same area and two-week period, scores it in bands from under 50% to over 300%, and combines it with the minimum infection rate per 1,000 females tested. CDC's vector index multiplies the average catch per trap night by the proportion infected, giving infected mosquitoes per trap night.

Where it does not

This is the part the brochure leaves out, so it is the part worth reading.

• Using CDC light traps or Culex gravid traps to monitor Aedes aegypti or Ae. albopictus. CDC says these species are not efficiently captured by the CDC miniature light trap, the CDC gravid trap or the New Jersey light trap. A zero from the wrong trap is not a zero.
• Estimating Culex infection from light-trap catches alone. CDC warns that light traps may collect fewer Cx. pipiens or Cx. quinquefasciatus, which gives small samples and less accurate infection rates. California notes that more than half of a CO2 trap's catch is newly emerged females that have never fed, and that these traps do not collect males or blood-fed and gravid females.
• Comparing numbers across trap types, or reading a count as the population. CDC describes abundance as the relative number of mosquitoes in an area during a sampling period. In New Orleans, trap type significantly changed estimates of abundance, richness and species mix. California asks for at least two years, preferably five, of history per trap type before calling a count above or below normal.
• Judging a source-reduction campaign by ovitrap counts. After source reduction, gravid females have fewer places to lay and put a larger share of eggs in the ovitraps. That can make the program look like it failed when it worked. CDC also says larval and pupal indices may not match adult abundance, and that thresholds should be set by each local program. State or national figures should be used with caution.
• New Jersey light traps near other lights, or for virus work. California lists them as ineffective where there are competing light sources. They select for night-active insects drawn to light, take a long time to sort because of by-catch, and deliver dead specimens that are less useful for virus detection.

Sources

• Mosquito Surveillance Traps — U.S. Centers for Disease Control and Prevention (2024)
• Surveillance and Control of Aedes aegypti and Aedes albopictus in the United States — U.S. Centers for Disease Control and Prevention (undated)
• West Nile Virus Surveillance and Control Guidelines — U.S. Centers for Disease Control and Prevention (2024)
• California Mosquito-Borne Virus Surveillance & Response Plan — California Department of Public Health, MVCAC and University of California (2026)
• Mosquito seasonality and trap type evaluation using routine surveillance data from New Orleans, Louisiana, United States — PLOS One (2026), PMC12788643