The Biology of Autogenous and Anautogenous Races of Culex pipiens L. (Diptera: Culicidae)

1. An English anautogenous race and three European strains of the autogenous race of Culex pipiens have been studied comparatively for 3 years under laboratory conditions.

2. Prolonged illumination has an activating influence on females of the anautogenous race, both hibernating and laboratory bred, and greatly stimulates gorging.

3. With the aid of artificial light during the winter months the anautogenous race has been kept breeding in the laboratory throughout the year for eleven generations without the occurrence of cyclical hibernation (asthenobiosis). Consequently it is suggested that the length of daylight may be a factor of importance in controlling the natural hibernation of females of this race.

4. Females of the English anautogenous race, whether of hibernating, or of active generations, laid normally after one blood meal and did not exhibit gonotrophic dissociation. They also oviposited readily after being artificially fed on bird blood.

5. Unfed females lived for a maximum of 19 days and never accumulated fat-body autotrophically.

6. Females, if fed on apple for 5 weeks, accumulated sufficient reserves to enable a small percentage of them to survive 15 weeks of starvation.

7. In the anautogenous race pairing always begins in the air although it may be completed on the ground. The females do not lay without a blood meal, and they show little tendency to bite man but bite birds voraciously.

8. Strains of the autogenous race of C. pipiens were obtained from rural areas in Greece, Malta and Hungary and have been maintained in the laboratory for over 3 years.

9. Continuous breeding under autogenous conditions (no blood meals) for several years and through forty-five to forty-nine generations has had no deleterious eflect on these autogenous strains.

10. Spanogyny, or the gradual decrease in the numbers of females produced in succeeding generations, does not necessarily follow prolonged autogeny if the cultures are kept under favourable conditions.

11. Males of the autogenous race pair with resting females, so that pairing can take place in very small areas.

12. Cross-mating was easily obtained between the two races, autogenous and anautogenous, in both directions: male autogenous + female anautogenous; and male anautogenous + female autogenous. Stenogamy and autogeny are hereditary characters. Stenogarny always appears in the F1 generation, but autogeny sometimes appears in the F1 generation and sometimes not until the F2 generation.

13. Eggs are quickly killed by temperatures below freezing-point; and young larvae die within 24 hours at 0° C. Adults, even hibernating females, die within 4 days at −16° C.