At least once a year GCMVCD staff strategically place 21 encephalitis virus surveillance (EVS) traps throughout Glenn County. EVS traps are set out overnight and retrieved the next morning and the contents are then returned to the district office for identification. GCMVCD staff will identify and sort the trapped live mosquitoes and pool the collections for virus testing. A pool, consist of 1 to 50 live female mosquitoes of the same specie. Pooled mosquitoes are transferred to numbered vials and sent to the Center for Vector-Borne Disease Research (CVBDR) at the University of California Davis. At the CVBDR lab the pools are tested for WEE, SLE, and WNV.