ABSTRACT
Since the incidence of mosquito-borne disease was drastically reduced by the use of DDT in the 1950s, the problem has again worsened and no single method of eradication seems likely to achieve lasting success. It now seems that the best hope lies in the combination of various methods of chemical control and perhaps genetic control to rid the Third World of its most important disease sector.
Subject(s)
Mosquito Control/methods , Pest Control, Biological/methods , Animals , Culicidae/genetics , Drug Resistance , Environment , Filariasis/prevention & control , Humans , Insect Hormones , Insect Vectors , Insecticides , Malaria/prevention & control , Pesticide ResiduesABSTRACT
The effects of PH60:40, an insect development inhibitor, on fourth instar larvae of Aedes aegypti were investigated. Apart from delayed lethal action, possible effects on the vectorial capacity of Brugia pahangi were investigated. Two strains of A. aegypti were used, one DDT-susceptible and a good filarial vector and the other DDT-resistant and a refractory vector. A baseline exposure was found which caused only low mortalities in both strains. The treatments did not have any appreciable effect on the vectorial capacity of the good vector strain, but modified the refractory nature of the poor vector strain. It was considered possible that this could be due to a generalized harmful stress of the treatment rather than to a specific action of the chemical. Larvae were therefore subjected to heat treatments, as an example of stress, and these produced similar mortalities as with PH60:40. They did not. however, alter the vectorial capacity of survivors of either strain, so that the effects described do not seem to be due to simple stress.
Subject(s)
Aedes/drug effects , Brugia , Filarioidea , Insect Vectors/drug effects , Aedes/parasitology , Animals , Female , Hot Temperature , Insect Vectors/parasitology , LarvaSubject(s)
Chagas Disease/prevention & control , Insect Vectors , Insecticide Resistance , Animals , TriatominaeABSTRACT
A questionnaire inquiring into the nature of schemes for the insecticidal control of disease vectors, the development of resistance in these vectors, and the effect of any such resistance on their control and on the extent of disease was sent to more than 100 health authorities throughout the world. The replies to the questionnaire are summarized in this paper.Until recently, the use of insecticides in public health has been largely based on three organochlorine compounds-DDT, HCH and dieldrin. However, in some countries resistance to these has now severely affected control both of many insect species and of the diseases they transmit (e.g., malaria, yellow fever, filariasis, typhus, plague). Certain other public health problems (onchocerciasis, Chagas' disease, trypanosomiasis, leishmaniasis) have not so far been greatly affected by resistance, but it is difficult to be sure of the continued reliability of the organochlorines.Research in the past 5 years, much of it sponsored by WHO, has shown the value of various organophosphorus and carbamate insecticides as replacements for the organochlorines, although resistance to them, too, can occur. Attention must therefore be focused on all facets of the use of these newer compounds and particular scrutiny made of possible instances of resistance to them.
Subject(s)
Insect Control , Insect Vectors , Insecticide Resistance , Public Health , World Health OrganizationABSTRACT
The interpretation of surveys of DDT-resistance in body-lice is handicapped by the fact that the genetics of this form of resistance have not been studied. This paper reports on a preliminary investigation on normal and resistant strains of lice, F(1) and F(2) hybrids of a mass cross and F(1) x R hybrids exposed to DDT dust and DDT-impregnated paper of various concentrations. The results were consistent with inheritance by a single gene pair (or possibly a small number of genes). The F(1) hybrids were intermediate in tolerance but were all killed by 5% DDT dust. This confirms a suggestion that 5% DDT dust would be suitable for testing for incipient resistance.
Subject(s)
DDT , Genetics , Insecticide Resistance , Phthiraptera , AnimalsABSTRACT
The three main subspecies of the Culex pipiens complex-pipiens, fatigans and molestus-have similar "normal" levels of susceptibility to insecticides. C. p. fatigans larvae resemble those of anopheline mosquitos in sensitivity to dieldrin, but are more resistant to DDT; the adults are unusually resistant to chlorinated insecticides, but do not differ greatly from other species of mosquito in susceptibility to organophosphorus compounds.There is evidence of conversion of DDT to DDE in C. p. fatigans and other mosquitos, but this may well not be the only cause of resistance. Dieldrin-resistance in C. p. fatigans involves cross-resistance to HCH, but at a considerably lower level; the mechanism of resistance is still obscure. Resistance to organophosphorus insecticides has been observed; the cross-resistance to diazinon indicates that the mechanism is not solely one of carboxy-esterase detoxication.Mechanisms of inheritance of resistance have been investigated. The most recent results indicate the monofactorial inheritance of resistance by a single pair of nearly dominant genes on chromosome 2 for DDT-resistance and by a single pair of genes on chromosome 3 with intermediate dominance for HCH dieldrin-resistance.
