INDUCED REGRESSION OF DIELDRIN-RESISTANCE IN THE HOUSEFLY (MUSCA DOMESTICA L.).
(73/504)
A high degree of resistance to cyclodiene insecticides, which appeared in a previously susceptible housefly strain maintained without exposure to insecticides but propagated from early-emerging adults to increase susceptibility to DDT, was found to be due to a single autosomal factor. Subsequent selection of a substrain for late adult emergence over 50 generations was unsuccessful in materially reversing the dieldrin-resistance or in demonstrating that selection of early-emerging flies was responsible for its appearance. However, selection and propagation of the knockdown-susceptible fraction of the population with lindane over 30 generations eliminated cyclodiene-resistance entirely. This method can be of value in maintaining laboratory strains at a normal level of susceptibility to cyclodiene insecticides. It is apparent, nevertheless, that various manipulations of a standard strain may affect its toxicological as well as other characteristics. The authors stress that when a standard reference strain is required for an extended period of time, it should be rigorously controlled and continuously evaluated. (+info)
DDT-RESISTANCE AND DIELDRIN-RESISTANCE IN ANOPHELES QUADRIMACULATUS.
(74/504)
The nature and mode of inheritance of both DDT-resistance and dieldrin-resistance in Anopheles quadrimaculatus from the United States of America have been studied. Dieldrin-resistance is shown to be dependent on a single, semi-dominant, genetic factor, and DDT-resistance on a single, recessive one, though the expression of this latter factor is to some extent dependent on the genetic background. Both resistances can occur in the same mosquito but can be separated, thus indicating the independent nature of the two genetic factors involved. (+info)
STUDIES ON AIRCRAFT DISINSECTION AT "BLOCKS AWAY" IN TROPICAL AREAS.
(75/504)
During 1962 experiments on disinsection of aircraft passenger cabins at "blocks away" (i.e., after the doors have been closed following embarkation but before take-off) were conducted with single-use, disposable aerosol dispensers in various types of commercial aircraft operating in the tropics. The favourable results of these trials and of previous trials in temperate zones indicate that this method is suitable as a standard procedure for aircraft disinsection for international quarantine purposes.The biological effectiveness of the SRA formulation against susceptible mosquitos and its non-irritancy to passengers render it suitable as a standard formulation for aircraft disinsection. The G-1492 formulation-effective against resistant and non-resistant mosquitos-could be used where insecticide-resistance is proved, although it is slightly irritant to some passengers. Both formulations are described. The authors suggest that further research is needed to develop a safe formulation that is effective against resistant and non-resistant insects and yet not irritant to passengers and crew. (+info)
THE CONVERSION OF DDT TO DDE BY SOME ANOPHELINES.
(76/504)
The metabolism of DDT has been followed in pure lines of laboratory-reared resistant and susceptible anophelines using gas-liquid chromatography. Relatively large amounts of DDE were formed in vivo by susceptible strains of Anopheles stephensi, A. quadrimaculatus and A. gambiae, and by resistant strains of A. stephensi and A. quadrimaculatus. Resistant and susceptible A. albimanus showed no difference in the rate of DDE production. Volatile metabolites of DDT other than DDE were not observed in most of the strains chromatographed. A procedure for the measurement of DDT-dehydrochlorinase in small numbers of mosquitos was devised based on conditions developed for the glutathione-dependent DDT-dehydrochlorinase present in resistant houseflies. This method has shown the enzyme to occur in highest titre in DDT-susceptible A. albimanus and A. stephensi, indicating little or no correlation with resistance to DDT. Major differences in dehydro-chlorination rates and in patterns of resistance between anopheline species have been observed. In A. stephensi, these differences extend to the level of strains. (+info)
SEASONAL VARIATIONS IN SUSCEPTIBILITY TO INSECTICIDES OF WILD-CAUGHT EAST AFRICAN ANOPHELES GAMBIAE.
(77/504)
Monthly tests of the susceptibility to insecticides of wild-caught Anopheles gambiae were made at two places in Tanganyika to see what seasonal variations might be revealed. Over a period of three years the susceptibilities were found to vary over a range of two to three times at different visits. The impression was at first gained that the susceptibilities to chlorinated hydrocarbon insecticides were in some way connected with the rainfall, but later work made this seem unlikely. Of all the factors considered which might affect the susceptibility only the temperature at the time of exposure could be found to have had an effect and it was concluded that this was largely responsible for the variations. (+info)
EXPERIMENTAL OBSERVATIONS GOVERNING THE CHOICE OF A TEST METHOD FOR DETERMINING THE DDT-IRRITABILITY OF ADULT MOSQUITOS.
(78/504)
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. (+info)
HEMATOLOGICAL DISORDERS FOLLOWING EXPOSURE TO INSECTICIDES.
(79/504)
The medical literature dealing with hematological disorders following exposure to insecticides (chiefly chlorinated hydrocarbons and organic phosphorus compounds) is briefly reviewed. The development of blood dyscrasias as a consequence of exposure to insecticides is considered unlikely. Reported cases are few in number and often involve persons with little contact with these materials. It is often impossible to prove (or to disprove) a cause-and-effect relation in the individual case. Pointers which may be of assistance in evaluating this relationship are described. Purpura as a result of allergic vascular changes after exposure to insecticides is also discussed. (+info)
THE HUMAN BLOOD INDEX OF MALARIA VECTORS IN RELATION TO EPIDEMIOLOGICAL ASSESSMENT.
(80/504)
The human blood index, or estimated proportion of the blood meals of a mosquito population obtained from man, is provisionally assessed for certain anophelines from blood-meal samples collected during the period 1959-62 and subjected to precipitin testing at the Lister Institute. In malaria eradication programmes this index is relevant to epidemiological assessment and to the modification of measures to interrupt transmission, since a mosquito's vectorial capacity and the malaria reproduction rate both vary as the square of the human blood index.There are serious difficulties in achieving representative sampling for this index and in interpreting the index obtained. These are discussed in some detail. In practice, the human blood index is often best estimated by applying the unweighted mean of a part-sample collected from human dwellings and one from other types of resting-place.Applying this calculation to the samples under review, it appears that DDT exerts a moderate, and dieldrin a more pronounced, impact on the human blood index of Anopheles gambiae and A. funestus; such an effect, indeed, may be general in house-visiting anophelines. Some 18 anopheline species are tentatively graded as having low, medium or high natural human blood indices. Regular and careful sampling, combined with recording of all relevant information, is recommended in view of the epidemiological and operational importance of the human blood index in assessment of eradication programmes. (+info)