Chlorpyrifos resistance

There have been many accidental spills of chlorpyrifos, but little quantitative assessment of its environmental effects. One exception is a spill in April 1985 in England (Boreham and Birch 1987). In that instance, a truck overturned, spilling 205 L chlorpyrifos into an adjacent stream that drained into the Roding River. A resulting sharp decrease in the number and type of macroinvertebrate benthic organisms in affected parts of the river, compared to unaffected areas, lasted 6 months. In addition, certain chlorpyrifos-resistant benthic organisms were unusually abundant. 

Milio, J.F., P.G. Koehler, and R.S. Patterson. 1987. Evaluation of three methods for detecting chlorpyrifos resistance in German cockroach (Orthoptera Blattellidae) populations. Jour. Econ. Entomol. 30 44-46. 

There are marked species differences in A-esterase activity. Birds have very low, often undetectable, levels of activity in plasma toward paraoxon, diazoxon, pirimi-phos-methyl oxon, and chlorpyrifos oxon (Brealey et al. 1980, Mackness et al. 1987, Walker et al. 1991 Figure 2.10). Mammals have much higher plasma A-esterase activities to all of these substrates. The toxicological implications of this are discussed in Chapter 10. Some species of insects have no measurable A-esterase activity, even in strains that have resistance to OPs (Mackness et al. 1982, Walker 1994). These include the peach potato aphid (Myzus persicae Devonshire 1991) and the... 

It is important to emphasize that the initial metabolites after hydrolysis may be both toxic and sometimes resistant to further degradation. Examples include nitrophenols, whose degradation is discussed in Chapter 9, Part 5 and 3,5,6-trichloropyridin-2-ol (Feng et al. 1997), which is produced by the hydrolysis of chlorpyrifos (0,0-diethyl-0-[3,5,6-trichlo-2-pyridyl]phosphorothioate). 

Ringo, J.. Jona, G.. Rockwell. R.. Segal. D.. and Cohen, E. Genetic variation for resistance to chlorpyrifos in Drosophila melanogaster (Diptera Drosophilidae) infesting grapes in Israel, /. Econ. Entomol, 88(5) 1158-1163,1995. 

The effect of these resistances has been to drive chemical control from one insecticide to the next. In most parts of the Nile delta the cotton leafworms can still be controlled by some OP compound, such as chlorpyrifos, supplemented where necessary with the insect growth regulator Dimilin. But in southern Texas, Mexico, Nicaragua and Peru the multiple resistances of the tobacco budworm, and to a less extreme degree of H. zea and Spodoptera sunia, have made even 20 insecticide applications a season quite worthless, and indeed there is less damage to the cotton if no chemicals are applied at all. The only materials that can be relied upon to kill these multiresistant H. viresoens are the dichlorovinyl pyrethroid NRDC-143 and the Heliothis nuclear polyhedrosis virus. 

The pest mosquito Aedes nigromacul Ls of the vast San Joaquin valley of California went resistant to organochlorines by 1951, to parathion by 1960, to fenthion by 1965, and to chlorpyrifos (Dursban) by 1970. At present reliance is placed on larvicidal oils, the juvenile-hormone mimic methoprene (Altosid) and the insect growth regulator diflubenzuron (Dimilin), — and on better management of surplus irrigation water. Residual sprays for housefly control, at first so spectacular with the organochlorines, had to move into the OP compounds, which were then knocked out in... 

The ability to cleave off the leaving group by a process presumably hydrolytic has been detected in a number of OP-resistant species (Table X). In the tobacco budworm clear evidence for OP-resistance being associated with oxidative cleavage was obtained from the action of microsomes on the phosphorothionate chlorpyrifos... 

Overproduction of OP-detoxifying esterases in mosquitoes was also demonstrated by an immunoblot method. Esterase Bi of C. qulnquefasclatus was shown to be overproduced by a factor of at least 500x, approximating the level of resistance to the OP insecticide chlorpyrifos (ca. 800x) as determined by bioassay (.22). ... 

The cotton bollworm, Helicoverpa armigera, in Australia is of great economic importance and is cross-resistant to parathion-methyl and profenofos, but not to chlorpyrifos. It has an acetylcholinesterase with low sensitivity to paraoxon-methyl and profenofos, but the sensitivity to chlorpyrifos is unaltered. As Table 9.3 shows, the enzyme of the resistant insects is a little less efficient by having a slightly higher Km. (Km is the substrate concentration at which an enzyme-catalyzed reaction proceeds at one-half its maximum velocity.) This indicates a somewhat less efficient enzyme, but the difference is so slight that it does not cause any reduced fitness for the insects. The amount of and activity of acetylcholinesterase are almost always much higher than strictly necessary. 

Lanning, C, Fine, R., Sachs, C., Rao, U., Corcoran, J., and Abou-Donia, M. (1996). Chlorpyrifos oxon interacts with the mammalian multidrug resistance protein, p-glycoprotein. J. ToxiccA. Environ, Health 47, 395-407. 

Ceil tv pes cultured 13 days on opposite surfaces of collagen-coated semipermeable membrane inserts (astrocytes preseeded on underside) chlorpyrifos (0.1 mVf-lO m,-)/) added to BMEC side in serum-free medium for 24 hr electrical resistance, morphology, and esterase activities measured. 

Studies examining the resistance of Culex pipiens quin-quefasciaius to propoxur, tcmcpho.s, and chlorpyrifos in Martinique (Yebakima et ai, 2004) and studies examining resistance of the same vector to malathion, chlorpyrifos, and other non-OP/CM insecticides in Alabama and Florida (Liu et al.. 2004) have revealed important but not unanticipated results. In all ca,ses, resistance and even cross-resistance to OP and CM insecticides and non-OP/CM insecticides were recorded in all species. 

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