Mixtures of insecticides

Dremova V.P., Frolova A.N. Baidarovtseva M.A. et al. Aktivnost i toksichnost binarnykh smesey insektitsidov (Activity and Toxicity of Binary Mixtures of Insecticides) / / Med. parazitologiya (Med. Parasitology). 1987. Issue 1. P. 40-43. 

Sabaliunas et al. (2000) showed that a Daphnia pulex immobilization test (Daphtoxkit F) was far more sensitive than Microtox to a mixture of insecticides seqnestered in SPMDs. This is not surprising because the OCPs and pyrethroid pesticides present in the enriched SPMD extracts are neurotoxins, and the effect thresholds can be much lower than narcosis-type toxicants. Thus, if insecticides are the contaminants of concern, the Daphtoxkit F approach may have some advantage over Microtox. 

With a molecular emission cavity flame detector, relying on measurement of the 526 nm emission of HPO (see Section II.C.l and III.B.3.b), nanogram amounts of phosphates or organophosphorus compounds can be assessed in automated systems160,348. Determination of m, the time elapsed between sample ignition and maximum emission, allows the resolution of ternary or more complex mixtures of insecticides. Dicrotophos, dimethoate, malathion and parathion mixed in aqueous solution were separated and identified in nanograms per millilitre concentrations348. 

Thin layer chromatography on alumina for separating mixtures of insecticides into their individual components and for a last stage of purification also for confirmation of identification. 

Alumina Fisher A-540, 80 to 200-mesh, to which 1% water is added. The activity varies slightly from lot to lot. To obtain an activity corresponding to that of the alumina used in collecting the data in Table I, calibrate each lot with a known mixture of insecticides. 

There is no cure. Remove and destroy infected plants. Control leafhoppers by spraying remaining plants with a mixture of insecticidal soap and 70 percent isopropyl alcohol (1 tablespoon alcohol to 1 pint soap solution). Spray 3 times, once every 3 days. Overwatering increases chances of the disease, particularly in heavy soils. 

A study in 26 men occupationally exposed to a mixture of insecticides, predominantly DDT, chlordane and lindane, found that the half-life of phenazone 10 or 15 mg/kg was reduced from 13.1 hours, in a group of 33 unexposed subjects, to 7.7 hours in the exposed group. The significance of this is unclear as changes in working practices have reduced occupational exposure to such chemicals. 

In some cases, insect species can develop resistance to organophosphorus insecticides, and this resistance has appeared in those species most intensively attacked. Mixtures of insecticides are sometimes far more effective than the sum of the individual component toxicities when used separately. This effect is known as potentiation. The reasons for potentiation are not fnUy understood but they may be connected with the exhaustion of some metabolising enzyme by one insecticide, leaving the other insecticide to work freely. 

Sulfur and its compounds are among the oldest and most widely used pesticides. Elemental sulfur is especially effective as a dust for the control of mites attacking citms, cotton, and field crops and as a protectant against chiggers, Trombicula spp., attacking humans. Sulfur also is a valuable fungicidal diluent for other dust insecticides and is used in wettable form as a spray mixture. Time sulfur has been a standard dormant spray for the control of the San Jose Quadraspidiotuspemiciosus and for other scales and various plant diseases. Time sulfur is a water-soluble mixture of calcium pentasulfide,... 

Pyrethroid Esters of Benzene Acetate. These insecticides have more extensive stmctural optimization in both acid and alcohol moieties. Fenvalerate [51630-58-17, a-cyano-(3-phenoxyphenyl)methyl (+)-(2R,5)"Ct"isoprop5i-4-chlorophenylacetate (24) d 1.17, vp 1.4 p.Pa at 25°C), a mixture of four isomers, is soluble in water to 0.3 mg/L The rat oral LD q is 450 mg/kg. Esfenvalerate [66230-04-4] is the (+)-2-(i, 5)-isomer (mp 59°C). The rat LD qS are 75, 458 (oral), and the rabbit dermal LD q is 2000 mg/kg. These pyrethroids are widely used general-purpose insecticides for field, vegetable, and fmit crops. 

Chlorinated Terpenes. A group of incompletely characterized insecticidal compounds has been produced by the chlorination of the naturally occurring terpenes. Toxaphene [8001-35-2] is prepared by the chlorination of the bicycHc terpene, camphene [79-92-5] to contain 67—69% chlorine and has the empirical formula C QH QClg. The technical product is a yellowish, semicrystalline gum (mp 65—90°C, d 1.64) and is a mixture of 175 polychloro... 

Other substituted phenyl A/-methylcarbamates that have been used for insect control include metalkamate [8065-36-9] a 1 4 mixture of y -(l-ethylpropyl)-phenyl A[-methylcarbamate [672-04-8] and y -(l-methylbutyl)-phenyl A/-methylcarbamate [2282-34-0], rat oral LD qS 87, 170 mg/kg, used as a soil insecticide MTMC [1129-41 -5], 3-methylphenyl N-methylcarbamate (mp 76°C), rat oral LD q 268 mg/kg, used for rice pests MPMC [2425-10-7], 3,5-dimethylphenyl A/-methylcarbamate (mp 79°C), rat oral LD q 380 mg/kg, used for rice pests TBPMC [780-11-0], 3-/ l -butylphenyl A/-methylcarbamate (mp 140°C), mouse oral LD q 470 mg/kg, for rice pests and butacarb [2655-19-8], 3,5-di-/ l -butylphenyl A/-methylcarbamate (mp 98°C), rat oral LD q >4000 mg/kg, for sheep blowfly larvae control. 

Lindane is one of eight different hexachlorocyclohexane (HCH), C H Cl, isomers and its Chemical Abstract n.2cniQ is la, 2a 3P, 4a, 5a 6P-hexachlorocyclohexane [58-89-9] (y-HCH or y-BHC, ben2ene hexachloride) (80). Commercial products containing lindane are marketed as either a mixture of isomers or as the pure y-BHC isomer. Not unexpectedly, lindane is a highly stable lipophilic compound and it has been used extensively worldwide as an insecticide. In contrast, hexachloropentadiene, C Cl, is an extremely reactive industrial intermediate used as a chemical intermediate in the synthesis of a broad range of cyclodiene-derived pesticides, which include endosulfan, endrin, heptachlor, and several different organohalogen flame retardants (81). 

Chemistry and Environmental Impact. Lindane is produced by the photocataly2ed addition of chlorine to ben2ene to give a mixture of isomers. The active y-HCH isomer can be preferentially extracted and purified. Composition of the technical-grade product is a (65—70%), B (7—10%), y (14—15%), 5 (7%), and S (1—2%). Lindane has been produced worldwide for its use as an insecticide and for other minor uses in veterinary, agricultural, and medical products. 

Synthetic pyrethroids is one of the group of modern insecticides of cyclopropancai bonic acid derivate. The pyrethroids prepai ation is the racemic mixture of optical isomers or mixture of cis- or tran.s-isomers. 

Much controversy has arisen regarding the ability of mixtures of weakly estrogenic compounds to act synergistically, notably the synergistic potential of mixtures of PCBs or of the insecticides dieldrin and toxaphene. " Recent studies suggest that the action of mixtures is at least additive. "... 

Tobacco and its alkaloids have long ceased to have any therapeutic importance, but their extensive use as insecticides and the demand for nicotine for the manufacture of nicotinic acid have stimulated interest in processes of extraction and methods of estimation. On the latter subject there is a voluminous literature, of which critical resumes have been published by various authors.Recent work on this subject has been specially concerned with (1) the development of miero- and semi-miero-methods suitable for estimating nieotine in tobacco smoke and the distribution of nieotine on sprayed garden produce, in treated soils and in tobaeeo leaves,(2) the study of conditions necessary to ensure satisfactory results in using particular processes, " and (3) methods of separation and estimation of nicotine, nomicotine and anabasine in mixtures of these bases. ) In the United States and in Russia considerable interest is being shown in the cultivation of types of tobacco rich in nicotine, in finding new industrial uses for tobacco and its alkaloids, and in possible by-products from tobacco plants such as citric and malic acids, i " Surveys of information on tobacco alkaloids have been published by Jackson, i Marion and Spath and Kuffner. ... 

Alkylamines have a variety of applications in the chemical industry as starting materials for the preparation of insecticides and pharmaceuticals. Labetalol, for instance, a so-called /3-blocker used for the treatment of hi h blood pressure, is prepared by SN2 reaction of an epoxide with a primary amine. The substance marketed for drug use is a mixture of all four possible stereoisomers, but the biological activity derives primarily from the (R,R) isomer. 

HCH, sometimes misleadingly termed benzene hexachloride (BHC), exists in a number of different isomeric forms of which the gamma isomer has valuable insecticidal properties. These were discovered during the 1940s, and HCH came to be widely used as an insecticide to control crop pests and certain ectoparasites of farm animals after the Second World War. Crude technical BHC, a mixture of isomers, was the first form of HCH to be marketed. In time, it was largely replaced by a refined product called lindane, containing 99% or more of the insecticidal gamma isomer. 

The first commercially available HCH insecticide sometimes misleadingly called benzene hexachloride (BHC) was a mixture of isomers, principally alpha HCH (65-70%), beta HCH (7-10%), and gamma HCH (14-15%). Most of the insecticidal activity was due to the gamma isomer (Figure 5.1), a purified preparation of which (>99% pure) was marketed as lindane. In Western countries, technical HCH was quickly replaced by lindane, but in some other countries (e.g., China) the technical product, which is cheaper and easier to produce, has continued to be used. HCH has been used as a seed dressing, a crop spray, and a dip to control ectoparasites of farm animals. It has also been used to treat timber against wood-boring insects. 

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