A STUDY OF THE GENETICS OF DIELDRIN-RESISTANCE IN THE HOUSEFLY (MUSCA DOMESTICA L.).
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Reciprocal mass crosses and back-crosses were performed between two homogeneous strains of the housefly (Musca domestica L.), representing the extremes in susceptibility and resistance to dieldrin. The heterozygotes were found to be intermediate between susceptible and resistant parents, and showed no evidence of sex linkage or cytoplasmic effects. The F(2) generation segregated in an approximate ratio of 1:2:1 into susceptible, heterozygote and resistant phenotypes, while the back-cross to the susceptible parent yielded 49.8:50.2 susceptible: resistant males, and 48.8:51.2 susceptible: resistant females. Elimination of susceptible forms in the back-cross progeny by use of a discriminating dosage and interbreeding the survivors produced offspring segregating into 26% susceptible, 50.1% heterozygote and 23.9% resistant, in excellent statistical agreement with a ratio of 1:2:1 expected in simple Mendelian inheritance. It is concluded that resistance to dieldrin in the housefly strain studied is due primarily to a major single pair of alleles or to a number of closely linked alleles so that they are inherited as a single unit. (+info)
INDUCED REGRESSION OF DIELDRIN-RESISTANCE IN THE HOUSEFLY (MUSCA DOMESTICA L.).
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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)
CHEMICAL AND BIOLOGICAL BEHAVIOUR OF FENTHION RESIDUES.
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Previous experiments at the University of California Citrus Research Center and Agricultural Experiment Station indicated that compounds incorporating the methylthiophenyl group-such as the insecticide fenthion-were highly susceptible to oxidation. Since the stability of fenthion and the properties of its degradation products have an important bearing not only on the efficacy of the insecticide but also on its toxicity to mammals under operating conditions, studies on the chemical and biological behaviour of fenthion and its residues have recently been carried out at the Center.The activity of fenthion against susceptible and resistant houseflies and mosquitos was compared with that of its principal oxidation products. Most of these products were similar to fenthion in their activity against houseflies, but appeared to be much less water-stable since they were considerably less effective against mosquito larvae. Stability tests showed that, in the presence of sunlight and air, fenthion was completely transformed into its sulfoxide and sulfone oxidation products within one to three days, and that these products were rapidly decomposed to non-insecticidal compounds. Upon heating, fenthion was rapidly isomerized to the S-methyl isomer. (+info)
MERMITHID PARASITES OF BLACKFLIES.
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Mermithid nematodes parasitize invertebrates only. A general account is given of their parasitism and the consequent mortality of blackflies. The author begins with a review of records of mermithid and blackfly association from different parts of the world and comments on the global distribution of the parasite. He discusses the life-histories of the parasites, stressing their adaptations to the moving environment of the aquatic stages of the blackfly and to the aerial environment of the adult. It is noted that the parasite usually kills its host upon emergence and has a restricted host range. Mermithids must be considered as selective mortality factors against blackfly populations. A survey of European and North American literature leads to conclusions concerning the role of the parasite in the natural regulation of blackflies. The possibility of utilizing these nematodes as biological control agents is discussed. (+info)
THE TOXICOLOGY OF CHEMOSTERILANTS.
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Sterilization of males can in certain circumstances be more efficient than killing as a method for control of insects and perhaps other pests. A number of chemicals (chemosterilants) show promise of producing sexual sterility in insects without some of the practical limitations of radiation. The most important compounds are alkylating agents. These have little immediate pharmacological action, but are notable for their selective action against haematopoietic and some other proliferating tissues. A number of alkylating agents have been shown to be mutagens in insects, bacteria, fungi, and higher plants; carcinogens in mammals; and teratogens in insects, birds, and mammals. Some produce sexual sterility, possibly in mammals as well as in insects, at doses too low to produce the other effects. Some have an established reputation as drugs for palliative treatment of leukaemia and other neoplasms.The development of insect sterilization as a vector control technique has been handicapped in part by lack of scientific information on the acute and long-term hazards that might be associated with the use of chemosterilants. In this paper the author brings together the available knowledge on the toxicology of the alkylating agents. (+info)
A MODIFIED TEST METHOD FOR MEASURING RESISTANCE TO DICHLORVOS VAPOUR.
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The growing use of dichlorvos as a residual fumigant implies the need for a test for possible resistance to dichlorvos vapour by mosquitos and other insects. A tentative method described by the WHO Expert Committee on Insecticides involves the use of 5-litre flasks, but these are inconvenient for field use. The present paper describes a modification of this test with more compact equipment. Two plastic Petri-dish halves are held facing together in a Perspex ring and separated by nylon mosquito gauze. The dichlorvos vapour is emitted from a small measured drop of a dilute solution in one half of the apparatus and the toxic effects are judged from rate of knockdown of insects confined in the other half.This simple test method has been tried out under various conditions of temperature and humidity. Relations between vapour emission and leakage were studied by bio-assay, to find a suitable solvent mixture and concentration. In its final form, the method gives satisfactory results with three kinds of mosquito, the housefly and a blowfly. (+info)
The regulation of flow through residual spray nozzles. 1. Metering orifices in polyethylene discs.
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Used residual spray nozzles, which have been discarded because of the increase in discharge rates, may be used again if their discharge rates are reduced by a metering orifice placed in the nozzle tip. A suitable orifice in a polyethylene disc is described. On the basis of laboratory test results, such a disc appears to be an inexpensive and satisfactory metering device for use in combination with worn spray nozzles. (+info)
Tests with organo-phosphorus dry sugar baits against houseflies in Israel.
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Tests were carried out in rural areas in Israel with various organo-phosphorus dry sugar baits. Malathion 2.5%, diazinon 1% and Dipterex 1% gave equally effective results. Chlorthion 1% and malathion 1% and 2% were used in smaller quantities and were less effective.Dry poisoned baits are considered an important supplementary measure to a rural fly control programme, especially when used as an adjunct to basic sanitation. (+info)