Residues, Insecticides

The potential use of economic poisons in this specialized field may be stated as follows The use of fumigants will increase, but no faster than the construction of improved storage facilities which will permit the efficient use of fumigants. Residual insecticides will increase in use for many years, but the total tonnage will not be high. In a few countries,... 

State and Municipal Health Department Requirements for Use of Common Residual Insecticide Sprays... 

Medical Management No specific viral therapy exists so treatment is supportive only. Treat patients with uncomplicated VEE infection with analgesics to relieve headache and myalgia. Patients who develop encephalitis could require anticonvulsants and intensive care to maintain fluid and electrolyte balance, ensure adequate ventilation, and avoid complicating secondary bacterial infections. Patients should be treated in a screened room or in quarters treated with residual insecticide for at least five days after onset, or until afebrile (without fever) to foil mosquitoes since humans may remain infectious for mosquitoes for at least seventy-two hours. Isolation and qaurantine is not required. Standard Precautions should be practiced when dealing with infection control for VEE victims as shown below ... 

Formulation and Structure of Residual Insecticides for Bark Beetle Control... 

A crucial omission in the research on residual insecticides for bark beetle control has been the absence of corollary studies relating control effectiveness to the physical structure of insecticide deposits on and in bark. The importance of deposit structure has been well documented (3, 21, 36). The structure of the deposit affects its availability to the insect contacting it and governs its toxicity. On an absorbent surface like bark, two major types of residues can be created deposits on the surface and deposits in the bark tissue. Henceforth, these will be referred to as surface and tissue deposits, respectively. Dusts and wettable powders form surface deposits. Solutions and emulsions penetrate and form mainly tissue deposits, though they may not remain in the tissue. The insecticide may crystallize out of solution, forming a deposit of fine crystals on the bark surface. 

A study of the structure of surface deposits of residual insecticides aimed specifically at bark beetle control was undertaken between 1956 and 1962 at the U.S. Forest Services Pacific Southwest Forest and Range... 

Space spray treatments have their limitations in that they will only control insects present at time of treatment and the insecticide will not penetrate deeply into cracks and crevices where many insects live. Consequently, frequent treat -ments are necessary for reliable control. Also, although insecticide will be deposited from space sprays onto horizontal surfaces and have some immediate effect, this will not he adequate to function as a residual insecticide. As a general hygiene precaution all food materials or surfaces upon which food will be handled are liable to deposition and must be covered during spraying. 

The product label describes the proper application rate for any specific residual insecticide as quantity of active ingredient (a.i.) per unit area usually mg (a.i.) m or mg (a.i.) ft 2. However, it is general practice to quote the concentration of product which should be applied toa surface either to point ofninoft" or as a coarse spray. The "point of runoff approach compensates for the lower effects from deposits applied to absorbent surfaces. Hven though considerable... 

Figure 5.1 Compression sprayer being used to apply a residual insecticide spray to control mosquitoes in Africa. Photo. G. A. Matthews...

DDT was first synthesized in 1874 and its insecticidal properties discovered in 1939. Technical DDT is a stable, white, amorphous powder composed of up to 14 analogs and isomers. In 1942, hexachlorocyclohexane (benzene hexachloride) was discovered to be an effective and simple insecticide. Of its isomers, y-HCH has the greatest insecticidal activity and is marketed as lindane, whereas a-HCH and )3-HCH are more toxic to mammals. Chlordane, a mixture of terpenoid compounds, was discovered in 1945 to be a highly effective residual insecticide. In 1948, the most active principle of chlordane, termed heptachlor, was developed, along with two other cyclodiene derivatives, aldrin and dieldrin. It has been subsequently shown that microbial conversion of heptachlor in the environment yields heptachlor epoxide, which exhibits toxicity equal to or greater than that of the parent compound whereas photochemical conversion yields the equally toxic photoheptachlor. Also during 1948, a product obtained by the chlorination of turpentine and containing a considerable number of chlorinated camphenes was sold as toxaphene. 

R. Pal, Methods for Studying the Behaviour of Malaria Vectors Under the Impact of Residual Insecticides. Document WHO/Mal/476.64 and WHO/Vector ControP89.64, Geneva, Switzerland World Health Organization, 1964, pp. 10. 

According to the WHO, an experimental hut is a simulated house, in which all entering, exiting, dead, and blood-fed mosquitoes can be recorded. Malaria campaigns pushed the development and use of experimental huts to evaluate the efficiency of residual insecticides, and they are still in use today to assess the impact of IRS or insecticide-treated bednets on local vector populations. The first experimental huts resembled typical African houses, but were standardized in shape, size, and furnishing to ease mosquito collections. Initially, huts were used to study insecticide toxicity... 

G. Davidson, Experiments on the effect of residual insecticides in houses against Anopheles gambiae and A.funestus, Bulletin of Entomological Research, 44 (2), 231,1953. 

R. C. Muirhead-Thomson, DDT and gammexane as residual insecticides a%din t Anopheles gambiae in African houses. Transactions of the Royal Society of Tropical Medicine and Hygiene, 43 (4), 401, 1950. 

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