The malaria parasite rates and densities were compared in 79 ovalocytic-normocytic pairs of Malayan Aborigines matched for age, sex, proximity of residence to each other, and use of bed nets when sleeping in their jungle settlement in central Peninsular Malaysia. Malaria infection was determined from thick and thin Giemsa-stained blood films collected monthly for a period of six months. Blood films from ovalocytic individuals were found to be positive for malaria less often than in persons with normal red blood cells (P less than 0.05). Malaria infections per 100 person-months at risk were 9.7 in the ovalocytic group compared with 15.19 in the normocytic group. Among individuals parasitemic at any time, heavy infections (greater than or equal to 10,000 parasites/mm3 of blood) with Plasmodium falciparum, P. vivax, and P. malariae were encountered only in normocytic subjects, which comprised approximately 12.5% of the malaria-positive individuals in this group. In an earlier survey of 629 settlers that identified subjects for the above study, the prevalence of ovalocytosis was found to increase significantly with age. The above field observations support the view that ovalocytic individuals might have a survival advantage in the face of malaria. Consideration of the ovalocytic factor is indicated in future evaluations of malaria control measures in areas where ovalocytosis is prevalent.

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Cytogenetic observations conducted on 9 strains belonging to the leucosphyrus group (Colless 1956) and their hybrids have revealed the evolutionary facts of the process of divergence among them. Previous paper (Kanda et al 1981b) reported some results of hybridization among them. Three strains-Bangkok (BKK), Kanchanaburi (KCH), and Chantaburi (CTB)-from Thailand can be designated as a subspecies Anopheles balabacensis dirus, with a small degree of divergence between the latter two strains. Two strains IMR and Kampong Sungai Ular (KSU) from Peninsular Malaysia can similarly be classified as a subspecies Anopheles balabacensis balabacensis B, while the strain Kota Belud (KTD) from Sabah with different genetic characters can be designated as a subspecies Anopheles balabacensis A. These 3 subspecies are included in the balabacensis complex. The two strains from Sarawak (SWK and SWN) were confirmed as a separate species designated as Anopheles leucosphyrus sensu stricto (Kanda et al 1981a) but with homosequential chromosome banding patterns of the leucosphyrus group (Reid 1968). A strain from Taiwan (TSG) is more closely related to CTB than KCH. There may exist some other closely related geographical populations. However, the designation of TSG as a valid species Anopheles takasagoensis distinct from balabacensis can not be confirmed due to insufficient data. Interstrain floating rearrangements of banding patterns were observed in the XR arm of KCH, IMR and CTB strain as well as in the hybrids. Additional descriptions of 2 chromosomal polymorphisms within the species group are given.

Glucose phosphate isomerase (E.C. 5.3.1.9) and phosphoglucomutase (E.C. 2.7.5.1) were found to be polymorphic in a laboratory colony of Aedes albopictus. The glucose phosphate isomerase locus is represented by two alleles resulting in three genotypes, while the phosphoglucomutase locus is represented by at least five alleles giving rise to a total of 15 genotypes. The inheritance of these two enzymes is of the Mendelian type with codominant alleles. Present data indicate that these genes are not linked.Of 105 mosquitoes analysed for these two gene-enzyme systems, the frequencies for glucose phosphate isomerase alleles are Gpi (S)=0.68 and Gpi (F)=0.32, while the frequencies for phosphoglucomutase alleles are Pgm (A)=0.16, Pgm (B)=0.11, Pgm (C)=0.19, Pgm (D)=0.30 and Pgm (F)= 0.24. The frequencies of the three glucose phosphate isomerase genotypes are in accord with Hardy-Weinberg expectations (X 1 (2) =2.74). Similarly, the frequencies of the 15 phosphoglucomutase genotypes probably do not differ significantly from Hardy-Weinberg expectations (X 10 (2) = 18.45).

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