Seasonal Occurrence, Egg Production, and Blood-feeding Activity of Autogenous Culex tarsalis1,2

Abstract

Studies were made in 1970 and 1971 of the seasonal occurrence, egg production, and blood-feeding activity of autogenous Culex tarsalis Coquillett in the northern Sacramento Valley, Calif. Autogeny first appeared in females reared from field-collected pupae in April, although pupae were first collected in March. Autogeny rates increased as summer progressed and surpassed 95% in some collections in July and August. Rates decreased in the fall until pupae could not be found in December. No autogenous egg development was detected from November through February in overwintering females collected from shelters, and about 95% of the females were nulliparous. The number of eggs in individual autogenous females reared from pupae collected from April to November ranged from 1 to 215, with a mean of 90. This compared with means of 189 and 144 for blood-engorged and gravid females, respectively, collected from June to October. There was a positive correlation between autogenous egg production and autogeny rates. Autogenous egg development at 25°C surpassed the normal ovarian resting stage within 60 h of adult emergence and was completed within 120 h. Females that were empty when collected in CO2-bait traps seldom (if ever) developed autogenous eggs when incubated for 5 to 10 days. Relatively few nulliparous autogenous females took blood when given continuous access to a chicken for 124 h from emergence.