Identification and linkage relationships of three hexokinase genes in Aedes aegypti

Biochemical taxonomy and enzyme electrophoretic profiles during development, for three morphologically similar Aedes species (Diptera: Culicidae) of the subgenus Stegomyia

Aedes (Stegomyia) cretinus is a rarely documented mosquito with a Mediterranean distribution, whereas Aedes (S.) albopictus has spread worldwide in the past two decades because of its anthropogenic associations. A third closely related species, Aedes (S.) flavopictus, is sympatric with A. albopictus in northeast Asia. The three species are characterized by a striking mid-thoracic white stripe and, consequently, field-collected individuals may be difficult to separate by morphology. Sixteen biochemical markers were described for laboratory strains representing the three species; these provided the first biochemical genetic profile for A. cretinus and A. flavopictus. Diagnostic enzymes for identifying each species pair were determined. A biochemical key was provided to distinguish among adults of the three species. Several enzyme loci that were diagnostic for the adult stage proved unreliable for identifying immature stages. Voucher specimens for link-reared series of larva, pupa, adult male, and adult female stages of the A. cretinus Crete strain (n = 88) and the A. albopictus Nepal strain (n = 105) were deposited at the Yale Peabody Museum of Natural History, New Haven, CT.

Chemical and gamma-ray mutagenesis of the white gene in Aedes aegypti

A molecular understanding of an insect gene can be facilitated by analysing the phenotypes of mutants for that gene. Protocols were developed for both chemical and gamma-ray mutagenesis in Aedes aegypti using the white (w) gene as an assay. Wild-type adult males were subjected to varying doses of either ethyl methanesulphonate (0. 1%, 0.5% or 1%) or gamma rays (1500 R or 3000 R), mated to females homozygous for the recessive w mutation, and progeny screened for the w phenotype, indicating non-complementation. The expression of newly induced w alleles was either complete or mosaic. Gamma-ray mutagenesis resulted in high (1.65 or 6.39%, depending on dose) induction of mutant alleles for the w gene, but not for a different gene, red-eye (0.15%). Gamma-ray-induced w alleles did not revert at a reasonable frequency following additional irradiation, suggesting that the high rate of gamma-ray-induced w mutagenesis is not due to a transposon insertion event.

Isoenzymes related to flight activity in Tetragonisca angustula (Hymenoptera:Apidae:Meliponinae): evidence of postranslational modification of the hexokinase and detection of new glycerol-3-phosphate dehydrogenase variants

To detect genetic markers, electrophoretic analyses were carried out on Tetragonisca angustula, a stingless bee well adapted to its wide area of occurrence, which is becoming economically important because of the quality of its honey. Polymorphism of the enzyme hexokinase was detected and it was demonstrated that, although it presents two bands in meliponines, this enzyme is under the control of a single locus whose product probably undergoes postranslational modification. The more common allele occurs in the two Tetragonisca subspecies studied here, but the other seems to be characteristic of only one subspecies. Four variants involving the two glycerol-3-phosphate dehydrogenase loci are also described. These two enzymes share the property of presenting two electrophoretic bands, one of which is characteristic of actively flying adult thoraces.

Genetic studies on hexokinase in the mosquito Aedes togoi

Hexokinases (EC 2.7.1.1) were genetically analyzed in the mosquito Aedes togoi by agar gel electrophoresis. Enzyme activity was observed anodally in one major banding region (HK-1) on the gel and in another faintly stained region (HK-2). A total of six bands was detected in the HK-1 region. All six bands could be detected in three body parts, head, thorax, and abdomen, of adults with different banding intensities. The third and fourth bands, numbered from the more anodal side, showed the broadest substrate specificity and the greatest enzyme activity throughout development. Genetic analysis of the six HK-1 bands was undertaken on the hypothesis of a single gene locus (or three extremely tightly linked loci). The analysis gave the following gene order: HK-1--4.2 +/- 1.8 (recombination units +/- SE)--To-2--Odh-2--29.5 +/- 2.5--sex (M/m)--s. A comparison is made of gene loci for hexokinases among the mosquito species Culex pipiens, Aedes aegypti, and this species, along with a comment on linkage relationships between Hk and Odh (octanol dehydrogenase) loci in three Aedes species.

Linkage relationships of eleven enzyme loci in the Aedes scutellaris group

Linkage relationships of 11 enzyme loci were determined in backcrosses between Aedes polynesiensis and Aedes kesseli. Three linkage groups established were Aat2-Lap2-Me-Sex, Cat-Ao-Pgm-Idh2-Est6, and Gpi-Odh-Pgd. Lap2 and Cat have not been previously mapped in Aedes. Locus order and linkage groups were the same as those observed for seven loci mapped in Aedes aegypti. The significance of the observed similarities in chromosome organization and differences in crossover values among closely related Aedes are discussed.

Genetic control of hexokinase variation in insects

Hexokinase variation in insects appears to be under the control of a single locus in some species and under multiple-locus control in others. It is often difficult to distinguish the number of loci controlling hexokinase expression. Analysis of hexokinase electrophoretic patterns in six species of mosquitoes and five species of crickets, as well as a review of hexokinase variation in other insect species, is used to emphasize the importance of interspecific comparisons when making genetic inferences. Evidence is provided which adds support for multiple hexokinase loci in dipterans. Hexokinase control by multiple loci may be difficult to determine in some species because of tight linkage, disequilibrium, and/or posttranslational modification.

Genetics of glucosephosphate isomerase in Aedes togoi (Diptera: Culicidae)

The genetics of glucosephosphate isomerase (E.C. 5.3.1.9) in two strains (Malaysian and Taiwan) of Aedes togoi is reported. Three electrophoretic phenotypes were presented in both sexes. The zymogram patterns were identical in both strains of A. togoi. The phenotypes were governed by a pair of codominant alleles. The allele frequency of the slow-moving band was 0.63 in the Malaysian strain adn was 0,86 and 0.82 in F161 and F169 generations, respectively, of the Taiwan strain. The sample studied was in good accord with Hardy-Weinberg expectation.

A world-wide survey of genetic variation in the yellow fever mosquito, Aedes aegypti

Thirty-four populations ofAedes aegyptirepresenting the world-wide distribution of the species, were analysed for genetic variation at 19–22 isozyme loci. The species has an average expected heterozygosity of 0·129±0·045 based on 19 loci analysed in every population. Based on this genetic information, two major groups can be defined: the dark, often sylvan, African subspeciesformosusand the light domestic subspeciesaegyptiin Africa and the New World. Asian populations do not fall easily into either group. These results are related to models which have been proposed for the evolution of this species. AlthoughA. aegyptiwas introduced into the New Worldc. 350 years ago and has recently recolonized many areas following eradication programmes, no signs of founder effects are evident in this region. Asian populations, on the other hand, do show a significantly lower level of genetic variation compared to other populations. This may be related to the time of introduction ofA. aegyptiinto Asia and historical absence of yellow fever on the Asian continent.