Enzyme electrophoresis indicated that all Schistosoma mattheei eggs passed in the urine of humans derive from S. mattheei females in copula with S. haematobium males. It appears that S. mattheei males do not reach sexual maturity in man; however, S. haematobium×S. mattheei males possibly do.

Enzyme electrophoresis was conducted on 10 Schistosoma mattheei adult worm samples, comprising 270 individuals, collected from cattle in the Eastern Transvaal Lowveld. Glucose-6-phosphate dehydrogenase (G6PDH) was studied in all the samples and phosphoglucomutase (PGM) and malate dehydrogenase (MDH) in five populations each. Only one population was polymorphic for G6PDH. In this population, in addition to the allele found in all the other samples, a second allele occurred with a similar Rf value to S. haematobium. The two alleles were in Hardy-Weinberg equilibrium. MDH-1 exhibited two alleles. However, these alleles were not in equilibrium. In certain populations, heterozygotes occurred together with homozygotes of one of the alleles only. PGM was monomorphic in all the populations studied.

Seven geographically varied isolates of Strongyloides ratti were cloned. Each clone was examined for the degree of homogonic development of the free-living generation and by enzyme electrophoresis. Considerable variation was found between the clones in the degree of development that was homogonic. In Contrast, the clones were indistinguishable by enzyme electrophoresis.

Enzyme electrophoresis was used to examine genetic variation within and between populations of Echinococcus granulosus from domestic and sylvatic hosts in western and eastern Australia. Substantial genetic diversity was found within all populations. There was no evidence, however, of genetic differentiation between populations from different hosts or geographic areas. When isolates were grouped into previously described domestic or sylvatic strains on the basis of rostellar hook morphology, most (94%) of the genetic variation occurred within, rather than between strains. These results conflict with the currently accepted theory of separate domestic and sylvatic strains of E. granulosus on the mainland of Australia.

Five Barbus populations were analyzed by enzyme electrophoresis to verify hybridization between two species in Spain, B. meridionalis and B. haasi. Two populations supposed to be hybrid have been named B. meridionalis-2 and B. haasi-2 because of their morphological resemblance to the corresponding parent species. 88.9% of B. haasi-2 genes are of the "meridionalis" type, a value obtained using six loci distinguishing the two species. None of the individuals in this population was identified as an F1 hybrid. On the other hand, B. meridionalis-2 showed no sign of introgression and is thus a population of the pure species B. meridionalis. The absence of known current contact between the hybrid population and both parent populations and the present genetic results suggest that the hybridization is currently interrupted in the studied locality.

Electrophoretic studies were carried out on isozymes of Glossina pallidipes to determine whether there are any genetic differences between natural populations from an area free of sleeping sickness (Nguruman) and an area where sleeping sickness is endemic (Lambwe Valley) in Kenya. Out of 12 enzymes examined, two enzymes, GPI and PGM, showed high polymorphism in the two populations, while the other 10 enzymes were all monomorphic. At the GPI locus, at least five alleles were detected, and two alleles were found at the PGM locus. There was a difference in the frequency of isozyme patterns between males and females, indicating that the PGM locus is on the sex-linked chromosome (X-chromosome). Nei's genetic distance (D) was 0.00154 between the two populations, which is the value within the range for local populations in different organisms examined so far. Some difference between the two populations was found in the level of average heterozygosity (H) and in allelic composition of the GPI locus, that is, the Lambwe Valley population is more heterogeneous than the Nguruman population.

Electrophoretic studies of Guatemalan blackflies, Simulium ochraceum, the main vector of Central American onchocerciasis, were performed using isozyme patterns. A total of six larval and adult populations originating from four localities (a non-endemic area, Finca La Ruda, a low-endemic area, Finca Rincon, and two high-endemic areas, Finca Brote and Finca Recreo) were analyzed. The enzymes examined were adenylate kinase (AK), alkaline phosphatase (ALP), glucose phosphate isomerase (GPI), hexokinase (HK), isocitrate dehydrogenase (IDH), leucine aminopeptidase (LAP), malic enzyme (ME), and phosphoglucomutase (PGM). Of these, six enzymes, AK, ALP, HK, IDH, LAP, and ME showed no variation either within or among populations. GPI and PGM were found to be highly polymorphic in all of the six populations. χ2-test for fit to Hardy-Weinberg equilibrium (HWE) revealed that the distribution of the phenotypes of the two polymorphic enzymes was not significantly out of the HWE. A verages of values of proportion of polymorphic loci (P) and heterozygosity per individual (H) of the six populations were 0.234 and 0.084, respectively, each of which was similar to the values reported for different groups of organisms (Nei, 1975). Genetic diversity among populations was measured by FST and GST and both parameters showed that the non-endemic population from the Finca La Ruda (Dl) was greatly differentiated genetically from the other five populations. Estimates of genetic distance (Nei, 1975) showed that the Dl population was furthest from the other populations.