The "AFS (Arbovirus Field Station) Sweeper" was designed and constructed to collect mosquitoes from various resting sites in the southern San Joaquin Valley of California. The sweeper offers backpack portability and maneuverability, rapid exchange of screened collecting cartons, and increased suction from a 12-volt DC blower powered by 2 gel cell 6V8A batteries that are connected in series. Field trials demonstrated that when the sweeper was operated for either 10 or 15 minutes per collection, the unit was effective for collecting male and female Culex tarsalis, Cx. quinquefasciatus and Culiseta inornata from different types of vegetation associated with foothill and valley agricultural habitats. The male to female sex ratios of Cx. tarsalis collected by the sweeper were significantly higher in the habitats sampled than the ratios in concurrent collections from artificial shelters.