The Anopheles gambiae complex and malaria transmission around Kisumu, Kenya

Abstract

• 1.

  The environment surrounding Kisumu in Kenya is described, emphasizing the importance of the Nyando valley as a highly malarious area as compared with the Nandi and Kisii hills where only epidemic malaria occurs.

• 2.

  Available data on malaria transmission are summarized in detail. The varying seasonal importance of Anopheles gambiae as a vector in the different topographical areas is discussed.

• 3.

  Data resulting from a brief survey of the A. gambiae complex (November 10th–December 3rd, 1970) conducted during very hot and dry weather are presented to show that Species A and Species B resting in houses are differentially distributed in this part of Nyanza. Species B predominated in the lowlands and was prolific in the artificially irrigated areas. Species A predominated in the highlands. Both sibling species were well represented in sympatric association among foothills.

• 4.

  Only 3 females of A. gambiae (1A and 2B) were obtained from the experimental area of 23 square miles employed by the WHO for hut testing of fenitrothion for anopheline control.

• 5.

  Circumstances indicated that both Species A and Species B would have formerly occured more abundantly in this zone.

• 6.

  It is suggested that although Species A was found to be virtually restricted to the highlands and foothills at this season, populations of A would probably encroach into the lowlands during rainy periods.

• 7.

  Finally, WHO data on parous rates of A. gambiae at 2 localities near Kisumu are presented to show that Species B may continue reproducing at a greater rate than Species A as the dry season progresses.