Resistance organophosphates

Carboxylesterases are well-represented in insects and are sometimes important in the development of resistance to insecticides. Thus, a well-characterized carboxylesterase E4 is responsible for resistance to organophosphorus insecticides in the aphid (Myzuspersicae) [107]. In the California Culex mosquito, the esterase B1 is 500-fold more abundant in organophosphate-resistant than in susceptible insects. The increase of esterase levels is the result of gene amplification, i.e., the resistant animals have an increased number of copies of the structural esterase gene [108],... 

Pirimicarb is a selective aphicide against organophosphate-resistant green peach aphids on a wide variety of crops including cereals, fruits, potatoes, sugar beets, and vegetables. It kills insects by contact, translaminar, systemic action, and vapor. Its oral LD50 in rats is 147 mg/kg. 

Claudianos, C.L., Russell, R.J., and Oakeshott, J.G., The same amino acid substitution in orthologous esterases confers organophosphate resistance on the house fly and a blow fly, Insect Biochem. Molec. Biol., 29, 675,1999. 

Oppenoorth, F.J. and van Asperen, K., Allelic genes in the house fly producing modified enzymes that cause organophosphate resistance, Science, 132, 298,1960. 

Organophosphate resistance in M. persicae is due to the production of large amounts of carboxylesterase E4 that degrade as well as sequester these insecticides (12). This is believed to be the only biochemical resistance mechanism in this species in many countries, including the UK., continental Europe, Japan, and Australia (25.). E4 additionally confers low levels of resistance to carbamates and to (IS)-trans-permethrin (12). This esterase has been characterized extensively by toxicological, biochemical, immunological and molecular studies (2, 22, 22f 22, 22) ... 

The acaricidal activity of these formamidines is based on a mechanism which is entirely different from that of the chlorinated hydrocarbons, organophosphates and carbamates. Some of them are more toxic to organophosphate-resistant mites than to organophosphate susceptible ones (Dittrich, 1969). 

Pyrethroids The spread of organophosphate resistance amongst tick... 

Siegfried BD, Scharf ME (2001) Mechanisms of organophosphate resistance in insects. In Biochemical Sites Important in Insecticide Action and Resistance (Ed. I. Ishaaya), Springer Verlag Berlin, Heidelberg, pp. 269-291. 

It was determined that substitution of the 5 -position of thiophene resulted in improved activity, most notably against organophosphate resistant two spotted spider mites (Table VI). This series of substituted thienyl derivatives shows surprisingly little variation when tested against a susceptible strain of TSM. It is assumed that the unsubstituted thienyl moiety is susceptible to metabolic oxidation, and that simple substitution (for example, methyl) at the 5 -position stabilizes the compound toward these oxidative processes. 

Figure 2 A gene in Drosophila (a) has had a transposable element Docl420 inserted into the second exon (b), generating a new gene that confers organophosphate resistance, is evolving rapidly, and has increased in abundance in the past few decades (Reproduced with permission from reference 10. Copyright 2005 AAAS.)...

FALLANG, A., RAMSAY, J.M., SEVATDAL, S., BURKA, J.F., JEWESS, P., HAMMELL, K.L. HORS-BERG, T.E. (2004) Evidence for occurrence of an organophosphate-resistant tjrpe of acetylcholinesterase in strains of sea lice (Lepeophtheirus salmonis Krpyer). Pest Management Science, 60,1163-1170. 

The com rootworms Diabrotica barberi and D. virgijera were controUed in the U.S. com belt from 1954 to 1964 by soil appHcations of heptachlor and aldrin. A resistant race of the western com rootworm D. virgijera was first characterized in southeastern Nebraska in 1961 and spread rapidly throughout the entire com belt. Successive introductions of carbamate and organophosphate soil insecticides have increased the cost of com rootworm control from... 

In 1916, calcium arsenate [7778-44-1] dusted by airplane was used to control the boU weevil however, throughout many developments in effective insecticides, such as organophosphates, the boU weevils became resistant to poisons that were formerly effective (see Insectcontroltechnology). 

Organophosphate esters are among the most widely used classes of synthetic compounds in hydraulic fluids. They are used as anti-wear additives in mineral oil hydraulic fluids and are significant components in certain fire-resistant hydraulic fluids (FMC 1991c, 1991d, 1992a, 1992b Wills 1980). 

Organophosphate Ester Hydraulic Fluids. Organophosphate ester hydraulic fluids are used in applications that require a degree of fire resistance such as in aircraft. EPA (1992b) has noted that aircraft mechanics may have dermal exposures of 1,300-3,900 mg/day and that 2,200 aircraft workers are routinely exposed to tributyl phosphate, while another 43,000 mechanics may be exposed at various times. Estimates of worker exposure in other industries were not found in the available literature. General population and military personnel exposure to organophosphate ester hydraulic fluids is likely to be much lower than exposure to mineral oil hydraulic fluids because these fluids have more specialized uses. 

Organophosphate Ester Hydraulic Fluids. Populations with potentially high exposures to organophosphate ester hydraulic fluids include aircraft mechanics and other mechanics repairing and maintaining hydraulic equipment designed to operate near combustion sources that require fire resistant hydraulic fluids. 

Currently there are few insecticides registered as surface treatments to control stored-product insects. For years the organophosphate insecticide malathion was used as a surface treatment for structural facilities, but stored-product insects throughout the world have developed extensive resistance to malathion (Subramanyam and Hagstrum, 1996). Most of the resistance reports were generated from studies with bulk grains, but in the United States, resistance has been documented for field populations of the red flour beetle, T. castaneum (Herbst), and the confused flour beetle, T. confusum (DuVal), collected from flour mills (Arthur and Zettler, 1991, 1992 Zettler, 1991). Populations of the Indianmeal moth, the almond moth, and the red flour beetle collected from bulk peanuts and empty warehouses were also highly resistant to malathion (Arthur et al., 1988 Halliday et al., 1988). 

A newer class of insecticides is the pyrethroids. These are synthetic derivatives of pyrethrins, which are natural extracts from chrysanthemums. Pyrethroids have been developed to be more stable (and thus more effective as insecticides) than the pyrethrins, which are particularly instable in light. Pyrethroids are frequently used as broad-spectrum insecticides. They have high insect toxicity, but lower mammalian toxicity than their organophosphate or carbamate counterparts. Pyrethroids are still limited in effectiveness due to their environmental lability, their high cost, and their potential for resistance development. 

The avermectin natural products are pesticides possessing novel chemistry and mode of action. Cross-resistance has not been observed in laboratory or field studies with mites andinsects tolerant to commercially available organophosphate, carbamate, chlorinated hydrocarbon and pyrethroid pesticides. 

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