Surveillance is where our abatement program begins. Data collected directly impacts our decisions on the course of action we use to help control the mosquito population in the area. During our surveillance, we:
- Survey the district, mapping locations of breeding sites
- Place traps to monitor the adult mosquito population density
- Identify the species of mosquitoes found
- Test mosquitoes for the presence of disease
Our laboratory is the backbone of our surveillance program. They monitor the local mosquito population density and test for mosquito borne diseases in the area.
The principle method of monitoring adult mosquitoes is accomplished by using traps placed throughout the district. The two primary traps we use are the New Jersey light trap and the gravid trap. We utilize additional adult mosquito collection methods including aspirator sampling and dry ice (carbon dioxide) traps when necessary.
We routinely monitor 28 traps throughout the district:
- Nine light traps – set up in residential yards
- 19 gravid traps
New Jersey Light Traps
New Jersey light traps collect mosquitoes by utilizing a light source as the attractant. Mosquitoes fly towards the light source and are blown via a small fan into a collection jar. The trap’s light source and blower fan are triggered by a photocell; turning on at dusk and off at dawn, optimizing the collection to mosquitoes while minimizing the collection of non-target insects such as bees which do not typically fly after sunset. The most common type of mosquito caught in our light traps is the Aedes vexans, a floodwater species.
The second adult mosquito trap regularly used by the NSMAD is the gravid trap. Gravid traps are excellent for collecting Culex mosquitoes, the primary vector of West Nile virus (WNV) in Illinois. Female Culex mosquitoes are attracted to stagnant and organic rich water in which they lay their egg rafts after ingesting a blood meal. The gravid trap utilizes a tub filled with water that mimics this nursery source, attracting the female mosquitoes to land on the water and lay their eggs. A battery-powered fan blows the mosquitoes into a net for collection. A larval control product is placed in the water to prevent mosquito breeding in our traps.
BG Sentinel Traps
We incorporated BG Sentinel traps into the surveillance program in 2016, as part of the our Zika response plan and in response to the first detection of Aedes albopictus mosquitoes in the District. The BG Sentinel trap uses visual cues and a patented lure packet to attract host-seeking mosquitoes. This trap design is very effective in collecting Aedes aegypti (which is not present in the District) and Aedes albopictus mosquitoes. These are light-weight, battery powered traps that are deployed as needed to areas where we suspect Aedes albopictus mosquitoes occur.
Mosquitoes collected from our traps are brought back to our laboratory for identification and testing. The mosquitoes are frozen in order preserve the samples and ease this process. After freezing, every mosquito is counted and sorted by gender and species. The female Culex pipiens mosquito is the mosquito we are most interested in, as it is the primary mosquito that can transmit disease to humans in our area. The Culex mosquitoes are broken down into pools (50 per pool maximum) and tested for West Nile virus. Other collected mosquito species are discarded after quantity and species data has been recorded.
Our Testing Methods
Currently, we utilize Real Time quantitative Polymerase Chain Reaction (RT-qPCR) to test mosquito samples for West Nile Virus.
RT-qPCR testing is done by taking either a single mosquito or a pool of up to 50 mosquitoes and grinding them in a small vial with a saline solution. This grinding releases West Nile Virus particles into the solution. The samples are centrifuged at high speed to isolate mosquito fragments at the bottom of the tube. The saline solution containing West Nile Virus is processed to remove all fats, proteins and carbohydrates leaving behind only the genetic material (RNA and DNA). The cleaned sample is then utilized in a process that relies on the enzyme polymerase to greatly amplify the amount of DNA in the sample. The increase in DNA during the amplification process is optically detected with the help of a fluorescent dye. Samples that contain West Nile Virus will have amplification that can be detected by an increase in the fluorescence of the sample. Samples that do not have West Nile virus will fail to amplify and no increase in fluorescence is detected.