Cytogenetic studies in indoor resting An. gambiae s.l. complex in five selected localities from east, south, and southwestern parts of Ethiopia were conducted. An. arabiensis was the only cyto-species found. Close examination of the inversion polymorphisms revealed the existence of two more polymorphisms in the 2Ra and 2Rd inversions, in addition to those previously reported viz. 2Rb and 3Ra, by Mekuria et al. (1982) and White (1974). The study covered wide ecological and altitudinal ranges and the karyotype frequencies were in agreement with the Hardy-Weinberg expectations. However, it was not possible to correlate the relationship between the 2Rb inversion and altitude as has previously been reported by Mekuria et al. (1982). The adaptive value of the 2Rb to increase in altitude (Mekuria et al., 1982), in view of diverse ecological and climatic conditions in An. arabiensis in Ethiopia is open to question.

A study of the mosquito fauna of the Mwea Rice Irrigation Scheme, Kenya, carried out during 1984 and 1985 identified 13 species, with Anopheles gambiae s. l. comprising 65.71% of the total collection. X-chromosome identification of 652 semi-gravid females resulted in 649 (99.5 %) positive identifications of An. arabiensis, implicating it as the noxious member of the An. gambiae complex present. Inversion polymorphism of chromosomes 2Rb and 3Ra karyotypes was studied in one village population. Seasonal population changes were found to be heavily dependent on rice field surface water. Artificial irrigation for rice farming greatly extended the breeding period per year by linking up the two wet seasons. Adult females fed more frequently on bovids than humans. The mean percentage gonotrophic condition of all females caught in the villagesof Karima, Thiba, Mucii-wa-Urata and Rurumi by pyrethrum spray-sheet collections, miniature light-traps and exit window traps was 69 % bloodfed, 18 % unfed and 13 % gravid. These proportions were statistically shown to be within predictable limits over time and space. The sporozoite infection rate in adult females was 0.55% by manual dissections and 1.2% by the ELISA technique.