Encephalitis Mosquito – Culex tarsalis (Coquillet). The encephalitis mosquito is widely distributed west of the Mississippi River and is found occasionally farther east. It is the principal carrier or the Saint Louis Encephalitis and Western Equine Encephalitis viruses. This mosquito has a wide white band around the mid-point of the proboscis as shown in the picture. Click here for a FREE pest control consultation or call 1-855-PEACHTREE (732-2487).