Absence of enhanced detoxication of permethrin in pyrethroid-resistant house flies

The mechanisms of resistance to pyrethroids were studied in a permethrin-selected (147-R) strain of the house fly, Musca domestica L. Approximately 12-fold synergism was obtained with a mixture of (1R)-trans-permethrin:piperonyl butoxide (1:5) so that the resistance decreased from 97-fold to 22-fold. Tests with the esterase inhibitor S,S,S-tributyl phosphorotrithioate produced very little synergism in either the resistant (R) strain (1.6-fold) or the susceptible (S) strain (1.9-fold). An investigation of the microsomal components revealed that compared to the S strain, the R strain demonstrated twice as much cytochrome P-450 and cytochrome b₅ and double the rate of NADPH-cytochrome c reductase activity. In addition, the rate of p-nitroanisole O-demethylation was found to be six times greater in the R strain. An in vivo accumulation study showed that the R strain displayed a decreased rate of penetration of trans-[¹⁴C]permethrin. When treated at equitoxic doses the R strain was found to tolerate 50-fold more internal permethrin than the S strain. An in vitro metabolism study indicated that there was no difference between strains in the overall rate of metabolism of trans-[¹⁴C]permethrin. The evidence obtained supports the conclusion that several resistance factors are involved but that decreased sensitivity of the nervous system to the action of pyrethroids is the principal mechanism of resistance in the 147-R strain.     

Cross-resistance spectrum in pyrethroid-resistant Culex quinquefasciatus

Strains of Culex quinquefasciatus Say, selected with biopermethrin [(1R)-trans-permethrin] or with (1R)-cis-permethrin, were examined in the larval stage for crossresistance to 30 pyrethroids, DDT, dieldrin, temephos, propoxur, and two organotin compounds. The (1R)-trans-Permethrin-R strain [resistance factor (RF) = 4100-fold] and the (1R)-cis-Permethrin-R strain (RF= 450-fold) of C. quinquefasciutus were cross-resistant to all pyrethroids tested [RF= 12-fold for an allethrin isomer to about 6000-fold for (RS,RS)-fenvalerate] as well as to DDT (RF= about 2000-fold). However, they were not significantly Cross-resistant to dieldrin, temephos, propoxur, and the two organotin compounds. Changes in the alcohol moiety, structural isomerism, and susceptibility of the cyclopropane C-3 side chain to oxidative attack are important factors in determining the level of cross-resistance to various pyrethroids. Limited synergism of the pyrethroids by S,S,S-tributyl phosphorotrithioate and piperonyl butoxide (PB), and of DDT by chlorfenethol and PB, suggested that some non-metabolic mechanism, such as kdr, may be an important component of resistance to pyrethroids as well as to DDT in this mosquito.     

Pesticide interactions: Effects of organophosphorus pesticides on the metabolism,toxicity, and persistence of selected pyrethroid insecticides

The organophosphorus pesticides profenofos, sulprofos, O-ethyl O-(4-nitrophenyl) phenylphosphonothioate (EPN), and S,S,S,-tributyl phosphorotrithioate (DEF) administered intraperitoneally to mice at 0.5 to 5 mg/kg strongly inhibit the liver microsomal esterase(s) hydrolyzing trans-permethrin. Profenofos, EPN, and DEF at 25 mg/kg increase the intraperitoneal toxicity of fenvalerate > 25-fold and of malathion > 100-fold. Topically applied profenofos, sulprofos, and DEF significantly synergize the toxicity of cis-cypermethrin to cabbage looper larvae and house fly adults but these phosphorus compounds are much less effective in synergizing the toxicity of trans-permethrin. The magnitude of synergism appears to depend on the species, organophosphorus compound, and pyrethroid involved. Profenofos, sulprofos, and EPN do not significantly alter the persistence of trans-permethrin on bean foliage.     

Penetration and metabolism of topically applied permethrin and cypermethrin in pyrethroid-tolerant Wiseana cervinata larvae

The penetration, excretion, and metabolism of topically applied [¹⁴C]permethrin and [¹⁴C]cypermethrin have been examined in larvae of the porina moth Wiseana cervinata to determine the factors which affect body levels of unchanged pyrethroids. Metabolism was by hydrolysis and to a lesser extent oxidation and the primary metabolites were quickly conjugated to water-soluble products. Little excretion occurred and body levels of unchanged pyrethroids were dependent on the interaction of penetration and metabolism. cis-Cypermethrin was more resistant to metabolism than trans-cypermethrin and cis- and trans-permethrin. trans-Permethrin most readily penetrated into larvae. The body levels of unchanged permethrin were enhanced by pretreatment of larvae with the metabolic inhibitors carbaryl or piperonyl butoxide. Tolerance of the pasture pest porina to the synthetic pyrethroids is discussed in relation to these findings.     

Quantitative structure-activity studies of substituted benzyl chrysanthemates: 4. Physicochemical properties and the rate of progress of the knockdown symptom induced in house flies

A procedure to evaluate the knockdown activity of pyrethroids against house flies in which metabolic factors could be eliminated as far as possible was established. With piperonyl butoxide and NIA 16388 as the inhibitors of oxidative and hydrolytic metabolism, respectively, the “intrinsic” knockdown potencies of 22 substituted benzyl (1R)-trans-chrysanthemates and related compounds were determined 2.5–3 hr after topical application to house flies. From the intrinsic knockdown potency and the rate of progress of the knockdown symptom from the earliest stage of intoxication, a “penetration” rate constant was estimated by first-order kinetics using a two-compartment model. The rate constant was correlated quantitatively with the hydrophobic parameter of the molecule. The lower the hydrophobicity, the higher the rate constant within the range of compounds used in this study.     

Neurophysiological activity and toxicity of pyrethroids derived by addition of methylene,sulfur or oxygen to the chrysanthemate 2-methyl-1-propenyl substituent

Conversion of chrysanthemates to their cyclopropane, episulfide, and epoxide derivatives by addition of methylene, sulfur, or oxygen, respectively, to the 2-methyl-1-propenyl double bond yields products generally of reduced toxicity but enhanced neurophysiological activity and photostability. The reduced toxicity is established with cis-cyphenothrin derivatives administered intracerebrally to mice and topically to house flies and with cis-phenothrin derivatives applied topically to American cockroaches and house flies, even in the presence of piperonyl butoxide for the house flies. In contrast, cyclopropane, episulfide, and epoxide derivatives of phenothrin are more potent than the parent compound in eliciting repetitive firing following stimulation of a cercal sensory nerve of the American cockroach in vitro. The individual 1′R and 1′S isomers of epoxides derived from (1R,cis,αS)cyphenothrin, (1R,cis)phenothrin, and (1R,trans)tetramethrin differ in potency by up to 20-fold for insecticidal activity, >30-fold for intracerebral toxicity to mice, and ～100,000-fold in the cercal sensory nerve assay. In each case the epoxide isomer of higher R_f is more potent than that of lower R_f when derived from a trans-chrysanthemate and vice versa from a cis-chrysanthemate.     

Synthetic pyrethroids: Toxicity and synergism on dietary exposure of Tribolium castaneum (Herbst) larvae

The potency of six dietary pyrethroids, as toxicants and inhibitors of weight gain in first- and fourth-instar Tribolium castaneum (Herbst) larvae, decreased in the order of cis-cypermethrin and deltamethrin > trans-cypermethrin and cis-permethrin > fenvalerate and trans-permethrin. Dosages that reduced larval weight also delayed pupation and emergence, probably due to their antifeeding activity. Three oxidase inhibitors (piperonyl butoxide, O, O-diethyl O-phenyl phosphorothioate, and O-isobutyl O-prop-2-ynyl phenylphosphonate), at a dietary concentration of 100 mg kg^?1, had little or no effect on the toxicity of trans-permethrin, but strongly synergised the toxicity of cis-cypermethrin by about 3-, 3- and 10-fold, respectively. Piperonyl butoxide also synergised the toxicity of cis-permethrin, trans-cypermethrin and deltamethrin, but not that of fenvalerate. On the other hand, an esterase inhibitor, profenofos, did not enhance the potency of any of the α-cyano-3-phenoxybenzyl pyrethroids. Oxidases appear to be more important than esterases in pyrethroid detoxification by T. castaneum larvae.     

Synthetic pyrethroids containing a C–C triple bond

The three commercial synthetic pyrethroids containing a carbon–carbon triple bond, α-ethynyl-2-methylpent-2-enyl (1R)-trans-chrysanthemate, (S)-2-methyl-4-oxo-3-(2-propynyl)cyclopent-2-enyl (1R)-trans,cis-chrysanthemate and [2,5-dioxo-3-(2-propynyl)-1-imidazolidinyl]methyl (1R)-trans-chrysanthemate are reviewed with emphasis on their inventive histories. Their chemistry and efficacy are described briefly. The relationship between stereochemistry and the biological activity is also discussed. © 1998 SCI.     

Independent and joint biological activity of isomeric forms of synthetic pyrethroids

Various isomeric mixtures of pyrethroids were examined in topical application tests against houseflies, Musca domestica. On the basis of the activities of the separate isomers of 5-benzyl-3-furylmethyl (±)-cis,trans-chrysanthemate, it was shown that when combined in pairs to give the (±)-trans or (±)-cis or (+)-cis,trans mixtures the observed mortalities did not differ from those expected by simple additive action calculated by the harmonic mean. In contrast the (±)-cis,trans mixture showed considerable antagonism with a mortality only 60% of that expected. Similar evaluations using the separate and combined isomers of bioallethrin [(R,S)-3-allyl-2-methyl-4-oxocyclopent-2-enyl (allethronyl) ( + )-trans-[(1R,3R)-chrysanthemate] and the corresponding (+)-cis-(1R,3S)-chrysanthemate indicate antagonism calculated to be correlated with the content of the (R)-isomer of the alcoholic moiety. Hence the activity of the most active isomer of the “allethrin” series, (S)-3-allyl-2-methyl-4-oxocyclopent-2-enyl ( + )-trans-(1R,3R)-chrysanthemate, (S)-bioallethrin, is not fully realised unless it is present in pure form and a substantial part of the value of bioresmethrin (5-benzyl-3-furylmethyl ( + )-trans-chrysanthemate] as a killing agent is lost when the racemic form is used. In racemic mixtures there is mutual antagonism between pairs of isomers so that considerable masking of activity occurs.     

Selective inhibition of separate esterases in rat and mouse liver microsomes hydrolyzing malathion,trans-permethrin,and cis-permethrin

Separate esterase activities of rat and mouse liver microsomes hydrolyzing malathion, trans-permethrin, and cis-permethrin were differentiated on the basis of their sensitivities to inhibition by paraoxon and α-naphthyl N-propylcarbamate (NPC). In rat liver microsomes, the malathionhydrolyzing activity was more sensitive to both inhibitors and showed a different time course of NPC inhibition than the activities hydrolyzing the permethrin isomers. Paraoxon completely inhibited trans-permethrin hydrolysis, but only partially inhibited that of cis-permethrin. The paraoxonsensitive trans- and cis-permethrin-hydrolyzing activities were not differentially inhibited, but separate inhibition curves were obtained for the inhibition of trans- and cis-permethrin hydrolysis by NPC. The mouse liver esterase activity hydrolyzing trans-permethrin showed a similar paraoxon sensitivity to that of rat liver, but that the paraoxon-sensitive portion of the cis-permethrinhydrolyzing activity was 5.5-fold less sensitive to paraoxon than the corresponding rat liver activity and was clearly differentiated from the mouse liver trans-permethrin-hydrolyzing activity. The mouse liver malathion-hydrolyzing activity was 100-fold less sensitive to paraoxon and 14-fold less sensitive to NPC than the corresponding rat liver activity. Rat and mouse liver esterase activities hydrolyzed trans- and cis-permethrin at similar rates under standard assay conditions, but mouse liver esterases were 10-fold less active in hydrolyzing malathion. The higher specific activity of rat liver malathion-hydrolyzing esterases resulted from the greater apparent affinity and maximum velocity for malathion hydrolysis. These results demonstrate that the hydrolysis of malathion, trans-permethrin, and cis-permethrin by rat and mouse liver microsomal preparations involves several esterases with differing substrate specificities and inhibitor sensitivities.     

Indoxacarb resistance in the house fly, Musca domestica

Indoxacarb (DPX-MP062) is a recently introduced oxadiazine insecticide with activity against a wide range of pests, including house flies. It is metabolically decarbomethoxylated to DCJW. Selection of field collected house flies with indoxacarb produced a New York indoxacarb-resistant (NYINDR) strain with >118-fold resistance after three generations. Resistance in NYINDR could be partially overcome with the P450 inhibitor piperonyl butoxide (PBO), but the synergists diethyl maleate and S,S,S-tributyl phosphorothioate did not alter expression of the resistance, suggesting P450 monooxygenases, but not esterases or glutathione S-transferases are involved in the indoxacarb resistance. Conversely, the NYINDR strain showed only 3.2-fold resistance to DCJW, and this resistance could be suppressed with PBO. Only limited levels of cross-resistance were detected to pyrethroid, organophosphate, carbamate or chlorinated hydrocarbon insecticides in NYINDR. Indoxacarb resistance in the NYINDR strain was inherited primarily as a completely recessive trait. Analysis of the phenotypes vs. mortality data revealed that the major factor for indoxacarb resistance is located on autosome 4 with a minor factor on autosome 3. It appears these genes have not previously been associated with insecticide resistance.     

Stability of cypermethrin and cyfluthrin on wheat in storage

Cypermethrin and cyfluthrin were applied to wheat, which was stored for 52 weeks at 25 or 35°C, and either 12 or 15% moisture content. Total residues and the proportions of the four pairs of enantiomers, cis I [(αR),(1R)-cis + (αS),(1S)-cis], cis II [(αR),(1S)-cis + (αS),(1R)-cis], trans III [(αR),(1R)-trans + (αS),(1S)-trans], and trans IV [(αR),(1S)-trans + (αS),(1R)-trans] for each pyrethroid were determined at five intervals during storage. For all storage conditions, the cis I isomers were the most stable, and the trans IV isomers were the least stable. Calculated half-lives (weeks) for the pairs of enantiomers at 25°C (12% moisture) and 35°C (15% moisture) were: cypermethrin, cis I, 252, 62 and trans IV 66, 27; cyfluthrin, cis I, 114, 52 and trans IV 42, 23. The results suggested that one of the enantiomers of the cypermethrin trans IV pair was degraded faster than the other.     

DDT and pyrethroids: Receptor binding in relation to knockdown resistance (kdr) in the house fly

The nature of target site or knockdown resistance (kdr) to DDT and pyrethroids was studied by investigating specific binding of [14_C] DDT and [14_C] cis-permethrin to the previously established membrane receptors from the heads of susceptible (sbo) and resistant (kdr) strains of the house fly, Musca domestica L. In vivo studies showed the heads from sbo flies bound two to three times more DDT than those from kdr flies at all doses tested. Reduced binding was also observed in kdr flies in in vitro [14_C] DDT binding assays. Scatchard analysis indicated that kdr flies have the same affinity but fewer receptors per milligram protein in the CNS than sbo flies. Assays with [14_C] cis-permethrin also showed binding was much reduced in kdr flies in comparison with sbo flies. Based on these results, the nature of the target site insensitivity of kdr flies may relate to their having a reduced number of receptors for the insecticides.     

Potentiation of Super-kdr resistance to deltamethrin and other pyrethroids by an intensifier (factor 161) on autosome 2 in the housefly (Musca domestica L.)

An intensifier (factor 161) identified on the second autosome in a pyrethroid-resistant strain of houseflies (Musca domestica L.) was isolated and introduced into a strain with super-kdr. Unlike E_0.39, which on its own also confers very weak (< × 3) resistance to pyrethroids, factor 161 very strongly intensified super-kdr resistance to pyrethroids. Together, factor 161 and super-kdr conferred immunity to deltamethrin in female houseflies (LD₅₀ > 20 μg fly^?1) but produced much less intensification of resistance to WL 48281, the (1R)cis (αS) isomer of cypermethrin, which differs from deltamethrin only in having chlorine instead of bromine substituents in the acid side-chain. Intensification was strongly decreased by piperonyl butoxide and propyl prop-2-ynylphenylphosphonate (NIA) but was unaffected by S,S,S-tributyl phosphorotrithioate (DEF). This synergism suggests involvement of oxidative rather than esteratic metabolism in the intensification of super-kdr by factor 161.     

Separation and characterization of the pyrethroid-hydrolyzing esterases of the cattle tick, Boophilus microplus

The principal esterases present in homogenates of cattle tick larvae have been separated by gel filtration and preparative isoelectric focusing. Substrate specificities have been determined using trans-permethrin, trans-cypermethrin, p-nitrophenyl butyrate, and the pyrethroid analog, p-nitrophenyl-(1R,S)-3-(2,2-dichlorovinyl)-2,2-dimethylcyclopropanecarboxylate (t-NPDC). One of the esterases, with pI = 4.6, and molecular weight ～67,000, hydrolyzed the α-cyano-substituted pyrethroid, trans-cypermethrin, but not permethrin. The major esterase activity was found in the pI 5.6–5.8 region, and corresponded to a molecular weight of ～89,000. Small differences in substrate specificity and differences in the banding pattern after isoelectric focusing were detected between esterases of ticks of a pyrethroid-resistant strain (Malchi) and a pyrethroid-susceptible strain (Yeerongpilly). Rate constants were determined for the inhibition of the different esterases by the organophosphate coroxon and by naphthyl N-propylcarbamate, using p-nitrophenyl butyrate and t-NPDC as substrates.     

Actions of pyrethroid insecticides on insect axonal sodium channels

The actions of pyrethroid insecticides were tested on isolated giant axons of the cockroach Periplaneta americana, using oil-gap, single-fibre recording techniques. Current-clamp and voltage-clamp experiments were used to determine the actions of pyrethroids on axonal membrane potentials and ionic currents. Treatment with deltamethrin at micromolar concentrations caused gradual depolarisation of the axon accompanied by a reduction in amplitude of the action potential. This depolarisation was enhanced by an increase in stimulation frequency. Other synthetic pyrethroids: 3,4,5,6-tetrahydrophthalimidomethyl (1RS)-cis-3-[(RS)-2,2-dimethylcyclopropyl]-2,2-dimethylcyclopropanecarboxylate, biopermethrin and its (1S)-enantiomer, (1R)-tetramethrin, S-bioallethrin, bioresmethrin and its (1S)-enantiomer, cismethrin, and 5-benzyl-3-furylmethyl (E)-(1R)-cis-2,2-dimethyl-3-(2-oxothiolan-3-ylidenemethyl)cyclopropanecarboxylate (RU-15525, ‘Kadethrin’) were investigated. The (1S)-enantiomers were inactive, but all the other pyrethroids tested, apart from deltamethrin, induced prolonged negative (depolarising) after-potentials. All the treatments with the active pyrethroids resulted in the appearance of a voltage and time-dependent ‘maintained’ sodium conductance. The duration of this ‘slow’ conductance varied considerably depending on the pyrethroid under test. Clearly, the effectiveness of pyrethroids on whole insects is not determined only by the degree to which they directly modify the properties of sodium channels. Nevertheless, voltage-clamp experiments on isolated axons readily permit direct comparison of the actions of different pyrethroids on the sodium channels of insect neurones.     

Toxicity of some pyrethroids to the adult desert locust,Schistocerca gregaria forsk

The toxicity of a number of topically applied pyrethroids has been tested against adult male desert locusts, Schistocerca gregaria: the most potent proved to be 5-benzyl-3-furylmethyl (+)-trans-chrysanthemate (bioresmethrin) with a weighted mean LD₅₀ of 4.0 μg/g. The remaining compounds may be ranked in order of toxicity as follows: 5-benzyl-3-furylmethyl (±)-cis-trans-chrysanthemate (resmethrin) > 4-allyl-2,6-dimethyl-benzyl(+)-trans-chrysanthemate > 4-allylbenzyl (+)-trans-chrysanthemate > 2,4,6-trimethylbenzyl (+)-cis-trans-chrysanthemate > 2,3,4-trimethylbenzyl (+)-cis-trans-chrysanthemate > 2,4-dimethylbenzyl (±)-cis-trans-chrysanthemate; 2-methylbenzyl (±)-cis-trans-chrysanthemate. A small factor of synergism (4.2) was obtained with bioresmethrin following pre-treatment with sesamex, but with resmethrin the synergistic ratio (1.6) was of little practical significance.     

Pyrethroid toxicology in the frog

Adult Rana pipiens pipiens (Shreber) are highly sensitive to insecticidal α-cyano-3-phenoxybenzyl esters administered subcutaneously, i.e., LD₅₀ 0.13–0.35 mg/kg for deltamethrin and the most potent isomer of each of cis-cypermethrin, fenpropathrin, and fenvalerate and 0.65 mg/kg for (1R,αS)-trans-cypermethrin. Pyrethroids lacking the α-cyano substituent [pyrethrins, S-bioallethrin, kadethrin, and the Cis- and trans-isomers of (1R)-tetramethrin, (1RS)-resmethrin, (1R)-phenothrin, and (1R)-permethrin] vary greatly in their toxicity (LD₅₀ 0.14 to > 60 mg/kg) and the trans isomers are much less toxic than the corresponding cis isomers. The trans/cis specificity is due in large part to relative detoxification rates based on synergism studies with the resmethrin and permèthrin isomers and liver pyrethroid esterase assays with the permethrin and cypermethrin isomers. Poisoning by the noncyano compounds involves hyperactivity and tremors whereas by the cyanophenoxybenzyl esters involves tonic seizures and choreoathetosis, i.e., types I and II syndromes, respectively. Picrotoxinin, t-butylbicyclophosphate, and five other small cage compounds give a third type of syndrome with clonic seizures. Diazepam and its 2′-fluoro-4-methyl-4,5-dihydro analog (RO 5-3636) are more effective than 23 other compounds tested in protecting against deltamethrin toxicity. Diazepam is most effective in alleviating the Type II syndrome, intermediate with the type I syndrome, and is not active with picrotoxinin.     

Carboxylesterases from Boophilus microplus hydrolyze trans-permethrin

An esterase which hydrolyzes the ester bond of trans-permethrin has been partially purified from homogenates of larvae of the cattle tick. The final (gel filtration) step showed two distinct peaks of p-nitrophenylbutyrate-hydrolyzing activity. The trans-permethrin-hydrolyzing activity of the lower-molecular-weight enzyme cochromatographed with the p-nitrophenylbutyrate-hydrolyzing activity of that enzyme. Little trans-permethrin hydrolysis was observed in the high-molecular-weight peak. The yield of the low-molecular-weight enzyme increased on extraction of the homogenates with Triton X-100. Inhibition studies using the low-molecular-weight enzyme and trans-permethrin as substrate indicated that hydrolysis was due largely to a carboxylesterase (EC 3.1.1.1).     

Developmental changes in trans-permethrin and α-naphthyl acetate ester hydrolysis during the last larval instar of Pseudoplusia includens

The hydrolysis of trans-permethrin and α-naphthyl acatate by midgut, fat body, and cuticle homogenates from Pseudoplusia includens (Walker) was monitored during the development of the last instar. The midgut homogenates appeared to have two pH optima (7.6 and 8.6) for the hydrolysis of trans-permethrin, the fat body homogenates had one optimum (7.4–7.8), and the cuticle homogenates had a major optimum at 6.6. Hydrolysis of both substrates peaked during the late feeding stages for midgut and cuticle homogenates, although relative changes were not the same. Hydrolysis of trans-permethrin peaked during the late feeding stage in fat body homogenates, while hydrolysis of α-naphthyl acetate continually increased through the prepupal stage. Thus, the hydrolysis of α-naphthyl acetate is not necessarily associated with the hydrolysis of trans-permethrin. The LD₅₀ values for trans-permethrin on the different stages appeared to reflect the influence of hydrolysis.