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Biomedical subjects

G Davidson

Publications and source records attributed to G Davidson.

At least 109 records · Page 6Linked to original sources
PubMed1981

Field measurement of the effective dominance of an insecticide resistance in anopheline mosquitos.

Anopheles culicifacies that were susceptible, heterozygous, or homozygous resistant to HCH and dieldrin were differentially marked with fluorescent dusts and released twice weekly into village huts in Pakistan that had been sprayed with four different dosages of HCH to see which of the genotypes died and which survived. The three highest dosages killed all three genotypes in the first four weeks, and heterozygotes and susceptibles for at least 12 weeks. The lowest dosage killed all the susceptibles throughout the period, and all but 0.07% of the heterzygotes. Thus the resistance is effectively recessive at the higher dosages and unlikely to be selected rapidly, as long as the gene frequency is low to start with and the houses are sprayed regularly. Similar releases of partially and completely resistant A. stephensi, and completely resistant A. subpictus, showed greater survival rates on exposure to the high HCH dosages than the same genotypes of A. culicifacies.

Animals↗
PubMed1981

The nature of malathion resistance in a population of Anopheles culicifacies Giles.

Malathion resistance in a population of Anopheles culicifacies from Maharashtra State in India, which also showed resistance to a number of other organophosphorus compounds, was found to be dominant in its expression. Most of the crossing and back-crossing results involving a susceptible population of the same species from Sri Lanka indicated the possible involvement of more than one genetic factor. The existence of such a broad spectrum of resistance, and experiments involving the use of the synergists triphenyl phosphate and piperonyl butoxide both suggest the presence of at least two mechanisms, one involving the specific carboxylesterase and the other the less specific mixed-function oxidase system.

Animals↗
PubMed1981

Fenitrothion (OMS 43) resistance in the taxon Anopheles culicifacies Giles.

Two colonies of the taxon Anopheles culicifacies Giles (one from Maharashtra State and one from Gujarat State, India) produced 28 and 64% mortality rates, respectively, on 1% fenitrothion for 2 hours. Six-hour exposures were required to achieve mortalities of greater than or equal to 96% in both colonies.

Anopheles↗
PubMed1980

A genetic study of the susceptibility of Anopheles gambiae to Plasmodium berghei.

In a study of the genetics of susceptibility and refractoriness of Anopheles gambiae to Plasmodium species, nine generations of selection resulted in a completely susceptible line and an entirely refractory line to Plasmodium berghei (a rodent malaria). The F1 progeny from reciprocal crosses between the lines differed in their susceptibility to the parasite. Backcrosses to the parent did not produce proportions of susceptible and refractory individuals consistent with single gene inheritance or with cytoplasmic inheritance but the influence of a sex linked factor was demonstrated.

Animals↗
PubMed1980

Recent developments of insecticide resistance in some Turkish anophelines.

Susceptibility tests carried out since 1974 in both the field and the laboratory with Anopheles sacharovi, A. hyrcanus and A. maculipennis from Turkey have revealed resistance to organophosphate and carbamate insecticides in all three species, in the first two in the southern Chukurova plain and in the third in the northern area around Osmanjik. Resistance was indicated by significant survivals when exposed to dosages killing presumed susceptible strains of these and other anopheline species. The temperature at which the susceptibility tests were carried out had a marked influence on mortalities. Broad spectra of resistance were shown by all three species, though with interspecific differences, and are attributed to the extensive and intensive use of a wide range of chemicals for agricultural pest control. Of the insecticides readily available for house-spraying for malaria control, malathion would appear to be the one with the greatest potential usefulness.

Animals↗
PubMed1973

The practical implications of resistance of malaria vectors to insecticides.

Insecticide resistance is an inherent characteristic dependent on relatively simple genetic mechanisms. This seems to be especially true of dieldrin resistance in anopheline mosquitos, though less obvious in DDT resistance among these species; little is known as yet about the inheritance of organophosphate and carbamate resistance as it occurs in Anopheles albimanus. The speed of selection of resistance depends on the original frequency of the gene or genes involved, the nature of the resistance imparted, and the selection pressure of the insecticide. This in turn depends on the inherent toxicity of the chemical, the efficiency with which it is applied, the proportion of the mosquito population coming under its influence, and the behaviour of the mosquito. In the past, too much reliance has been placed on the determination of the LD(50) in assessing the presence or absence of insecticide resistance. Quite high incidences of resistant individuals can result in such small changes in the LD(50) that resistance may be overlooked. The use of single discriminating dosages is advocated, based on concentrations of insecticides that normally kill all susceptible individuals. The authors discuss such dosages in respect of dieldrin and DDT, and put forward newly-established tentative discriminating dosages for organophosphorus and carbamate insecticides, which await field confirmation.From a practical standpoint, an insecticide should not be abandoned or replaced by another as soon as resistance is confirmed. This may not be necessary where the degree of resistance is not high and the vector is not highly efficient. Certain procedures are proposed in order to assess the epidemiological and entomological implications of resistance before the insecticide concerned is abandoned.

Animals↗