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Biomedical subjects

A W BROWN

Publications and source records attributed to A W BROWN.

At least 19 recordsLinked to original sources
PubMed1965

DEHYDROCHLORINATION AND DDT-RESISTANCE IN CULEX MOSQUITOS.

The mechanism of resistance to DDT was investigated in Culex mosquitos to ascertain whether it was associated with detoxication to DDE as in houseflies and Aedes aegypti. Resistant larvae of C. tarsalis were found to effect this dehydrochlorination, whereas the susceptible larvae did not; resistant larvae of C. fatigans completely converted all the absorbed DDT to the metabolite DDE. Enzyme assays in vitro showed that the resistant C. fatigans had 10 times the dehydrochlorinating activity, and resistant C. tarsalis four times the dehydrochlorinating activity, of their susceptible counterparts. The DDT-dehydrochlorinase enzyme of C. fatigans resembled that of Aedes aegypti more than that of the housefly, though differing from it in at least one respect.

Aedes↗
PubMed1964

EXPERIMENTAL OBSERVATIONS GOVERNING THE CHOICE OF A TEST METHOD FOR DETERMINING THE DDT-IRRITABILITY OF ADULT MOSQUITOS.

In an attempt to determine the optimum test conditions for assessing the irritability of adult mosquitos to DDT, the author has carried out a series of experiments with two strains of Aedes aegypti, one resistant and one susceptible to DDT. In these experiments a comparison was made between, on the one hand, the results obtained with the three possible test steps included in a tentative method proposed in 1960 by the WHO Expert Committee on Insecticides, and, on the other hand, the results with those same steps to which modifications proposed by M. Coluzzi were applied.The conclusions drawn from these investigations are that Alternative Step B of the WHO Expert Committee method is the best test step, and that the optimum conditions for performance of this technique are provided by a combination of elements from both the WHO Expert Committee and the Coluzzi methods (2% DDT test papers, three-minute settling period, Coluzzi illumination). This is in fact the technique recommended as standard in 1963 by the WHO Expert Committee on Insecticides.

Aedes↗
PubMed1963

CHROMOSOME CHANGES AND INSECTICIDE RESISTANCE IN ANOPHELES QUADRIMACULATUS.

Certain insecticide-resistant strains of anopheline mosquitos found in the field or developed in the laboratory are known to contain a high proportion of heterozygotes for chromosomal inversions, but up till now it has not been clear how this could be causally related to resistance. In the present investigation, 2 resistant strains and 2 susceptible strains of Anopheles quadrimaculatus, and the hybrids between them, were examined for the frequency of inversions. It was found that neither the resistant nor the susceptible strains were characterized by inversion buckles. Moreover, no new inversions appeared in the hybrids between them. It was therefore concluded that where heterozygosity for inversions has been observed in anophelines, it is a characteristic of hybrids due to parental differences resulting from geographic separation, and has no relation to specific insecticide resistance.

Animals↗
PubMed1962

A survey of Simulium control in Africa.

It has become possible to control or even eradicate the Simulium fly vectors of Onchocerca volvulus, the causative organism of onchocerciasis. There are two vectors in Africa-namely, S. damnosum, characteristic of the rivers of West Africa, and S. neavei, which breeds on the carapaces of crabs in the streams of East Africa. The use of DDT applied to the water at a concentration as low as 0.1 p.p.m. for 30 minutes eliminates the larvae of Simulium. Such larvicidal methods have eradicated S. neavei from western Kenya and virtually eradicated S. damnosum from the Victoria Nile in Uganda. Excellent control sufficient to render the transmission of onchocerciasis almost negligible has been obtained at Léopoldville (Republic of the Congo) and in circumscribed areas in southern Chad, Northern Nigeria, and Sierra Leone. The following survey describes operational research on Simulium control carried out in Kenya, Uganda, the Congo, Chad, Nigeria, Ghana, Upper Volta and Sierra Leone.

Africa↗
PubMed1961

Genetical studies on dieldrin-resistance in Aedes aegypti and its cross-resistance to DDT.

A strain of Aëdes aegypti was recently found in Puerto Rico which proved to be resistant to both DDT and dieldrin. This paper reports on genetical studies of this strain to determine whether a single entity is involved or two distinct resistances. Tests carried out by repeated back-crossing combined with selection pressure from DDT and dieldrin and by crossing with a strain with marker genes indicate that a single entity is responsible (dieldrin-resistance with cross-resistance to DDT) and that its genetic factor is located on chromosome 2 at a distance of 25 from locus "yellow".

Aedes↗
PubMed1958

The insecticide-resistance problem: a review of developments in 1956 and 1957.

The author reviews the growth of the insecticide-resistance problem throughout the world during the period between July 1956 and November 1957, and the developments in research on the subject during the same period.Three new resistant species have been discovered-Anopheles subpictus, Chrysomyia putoria and Rhipicephalus sanguineus-and eight new types of resistance in already resistant species have been observed. Moreover, the geographical area covered by certain resistant insect populations has considerably increased.THE RESEARCH ACCOMPLISHMENTS DURING THE PERIOD UNDER REVIEW INCLUDE: systems of detecting resistance in the field by standard test methods; confirmation of two distinct types of resistance to chlorinated-hydrocarbon insecticides in mosquitos and bed-bugs as well as in houseflies; evidence that DDT-resistance in the housefly, Anopheles sundaicus and Aëdes aegypti is due mainly to a single genetic factor associated with the ability to dehydrochlorinate DDT, and that dieldrin-resistance of Anopheles gambiae also derives from a single factor present even in untouched populations; a fuller understanding of the physiological mechanism of BHC-resistance in the housefly; and demonstration that selection pressure from organo-phosphorus compounds induces resistance to themselves and to chlorinated-hydrocarbon insecticides.

Aedes↗
PubMed1957

Survey of possible insecticide resistance in body lice.

WHO inaugurated in 1953 a global survey of the susceptibility of the body lice to insecticides. The test used consisted, essentially, of treating a balbriggan type of cloth with dusting powder, placing the lice upon it, and assessing the mortality 24 hours later. The present paper describes the results of tests carried out in 37 countries. A significant resistance to DDT has been found to be present in many countries, and there are indications of several instances of BHC-resistance.

Animals↗