Increased herbicidal activity of triazine herbicides by piperonyl butoxide

Piperonyl butoxide (PB) is a known Synergist which enhances the activity of insecticides by inhibiting their biotransformation to less active products. We have evaluated the possible use of PB as a herbicide synergist using triazine herbicides in sensitive, tolerant, and resistant plants. The effects of PB, triazine herbicides, and their combinations were examined in whole plants as well as in chloroplasts isolated from triazine-sensitive (S) and -resistant (R) weed biotypes. PB itself, applied postemergence (0.1–0.5%, v/v), was slightly toxic to the plants tested. However, foliar application of PB combined with atrazine, terbutryn or prometryn to maize seedlings significantly increased the phytotoxicity of the herbicides. Low rates of atrazine, prometryn, and terbutryn in a tank-mixture with PB, effectively controlled Solatium nigrum L. and Abutilon theophrasli Medik. PB enhanced atrazine efficacy in both S and R biotypes of Lolium rigidum Gaud. The synergistic effect of PB was evident also in vitro when atrazine and methabenzthiazuron were used to inhibit photosystem II electron transport in chloroplasts isolated from resistant weeds. These data demonstrate the potential of PB as a herbicide synergist and its possible utilization as an aid for improving the activity of triazine herbicides in sensitive, tolerant and resistant plants.     

An analogue of piperonyl butoxide facilitates the characterisation of metabolic resistance

BACKGROUND: Previous work has demonstrated that piperonyl butoxide (PBO) not only inhibits microsomal oxidases but also resistance‐associated esterases. The ability to inhibit both major metabolic resistance enzymes makes it an ideal synergist to enhance xenobiotics but negates the ability to differentiate which enzyme group is responsible for conferring resistance. RESULTS: This study examines an analogue that retains the ability to inhibit esterases but is restricted in its ability to act on microsomal oxidases, thus allowing an informed decision on resistance enzymes to be made when used in conjunction with the parent molecule. CONCLUSION: Using examples of resistant insects with well‐characterised resistance mechanisms, a combination of PBO and analogue allows identification of the metabolic mechanism responsible for conferring resistance. The relative potency of PBO as both an esterase inhibitor and an oxidase inhibitor is also discussed. Copyright © 2008 Society of Chemical Industry     

Effects of the synergist piperonyl butoxide on metabolism of pesticides in green sunfish

The effects of piperonyl butoxide on metabolism of ¹⁴C-labeled methoxychlor, aldrin, and trifluralin were investigated in green sunfish, Lepomis cyanellus. Piperonyl butoxide inhibited epoxidation of aldrin to dieldrin, O-dealkylation of methoxychlor, and N-dealkylation of trifluralin, resulting in higher levels of total radioactivity in animals exposed to the combination compared to those exposed to pesticide alone. Where piperonyl butoxide was present a greater proportion of the total radioactivity in the fish extract occurred as parent compound compared to metabolites than in fish exposed to pesticide alone. After 16 days of exposure piperonyl butoxide increased the proportion of parent compound eight times for methoxychlor, 17 times for aldrin, and 15 times for trifluralin.     

Temporal synergism by microencapsulation of piperonyl butoxide and alpha-cypermethrin overcomes insecticide resistance in crop pests

A microencapsulated formulation that gives a burst release of piperonyl butoxide (PBO) several hours before a burst release of a conventional pyrethroid can effectively overcome metabolic resistance in Bemisia tabaci Gennadius, Helicoverpa armigera (Hübner), Aphis gossypii Glover and Myzus persicae Sulzer. This increase in efficacy against resistant pests was reflected in a field trial against B. tabaci on cotton, eliminating the need for two treatments. The ratio between the active insecticide and the synergist was found to be crucial in reducing resistance factors.     

Cockroach control in sewers in Singapore using bioresmethrin and piperonyl butoxide as a thermal fog

Cockroaches have considerable importance as vectors of disease. In tropical areas, large populations of Periplaneta americana may be found in sewers and the refuse chutes of large apartment blocks. These cockroach populations are not accessible to residual insecticide treatment with sprays but may be controlled with thermal fogs of pyrethroids. An experiment on the use of bioresmethrin (5-benzyI-3-furyimethyl-(+)-trans chrysanthemate) as 0.15% and 0.25% w/v solutions with equal amounts of synergist in kerosene discharged from a TIFA fog generator was made at Toa Payoh in Singapore. Effective control was obtained with 0.15% bioresmethrin plus 0.55% piperonyl butoxide in kerosene blown into the sewers and waste chutes initially, at four weeks, at eight weeks later and then followed by treatment every two months.     

Simultaneous estimation of bioresmethrin and piperonyl butoxide by gas-liquid chromatography with chemical-ionisation mass spectrometry

A technique using gas-liquid chromatography combined with chemical-ionisation mass spectrometry is described for the simultaneous quantitative measurement of bioresmethrin and piperonyl butoxide. It is sensitive to 0.2 ng bioresmethrin and 2 ng piperonyl butoxide. The amounts of these compounds, in extracts of 50-g samples of laboratory-fortified wheat, were determined.     

The use of piperonyl butoxide and MGK-264 to improve the efficacy of some plant-derived molluscicides

Synergism of an oil of Azadirachta indica, a powdered extract of Allium sativum bulbs and an oleoresin of Zingiber officinale rhizomes by piperonyl butoxide and MGK-264 was studied against the snails Lymnaea acuminata and Indoplanorbis exustus. The active components of these plant-derived molluscicides, respectively azadirachtin, allicin and [6]gingerol, were also combined with these synergists. Both piperonyl butoxide and MGK-264 enhanced the toxicity of all of the test compounds. The response of snails to the synergised mixtures was both time- and dose-dependent. © 1998 Society of Chemical Industry     

Cumene hydroperoxide-generated spectral interactions of piperonyl butoxide and other synergists with microsomes from mammals and insects

Piperonyl butoxide-dependent formation of type III difference spectra and the resulting inhibition of carbon monoxide binding by microsomal cytochrome P-450 were investigated using a cumene hydroperoxide-supplemented reaction medium. Cumene hydroperoxide is capable of supporting the formation of type III spectra with piperonyl butoxide and microsomes from several different species. NADPH is not required in the presence of cumene hydroperoxide. Similarities and differences between NADPH- and cumene hydroperoxide-mediated reactions were noted. Comparative studies indicated that, as in mammals, insect microsomal cytochrome P-450 also possesses peroxidase activity. In addition to piperonyl butoxide, other methylenedioxyphenyl compounds such as sulfoxide, n-propyl isome, and sesamol also give rise to a similar spectral response in either NADPH- or cumene hydroperoxide-supplemented reaction media. The significance of the cumene hydroperoxide-dependent reaction in elucidating the mechanism of synergistic action of methylenedioxyphenyl compounds is discussed.     

Effects of piperonyl butoxide and DEF on the metabolism of methoprene by the imported fire ant,Solenopsis invicta Buren

Studies are presented on the effects of two synergists, piperonyl butoxide and S,S,S-tributyl phosphorotrithioate, on the metabolism of methoprene [isopropyl (2E,4E)-11-methoxy-3,7,11-trimethyldodeca-2,4-dienoate], an insect growth regulator, by the castes of the imported fire ant, Solenopsis invicta Buren. In adults, but not in larvae, pharate pupae, and pupae, piperonyl butoxide, a microsomal enzyme inhibitor, reduced methoprene metabolism by blocking O-demethylation. S,S,S-Tributyl phosphorotrithioate, an esterase and microsomal oxidase inhibitor, was most effective in reducing methoprene metabolism in larvae. In toxicity studies, against pharate pupae, the O-demethylated methoprene metabolite (alcohol-ester) was shown to be more toxic than methoprene. Synergists may be useful in bait formulations used for imported fire ant control to extend the effectiveness of methoprene.     

Effect of binary combination of some plant-derived molluscicides with MGK-264 or piperonyl butoxide on the reproduction of the snail Lymnaea acuminata

The effects of sub-lethal treatments (20 and 60% of 24-h LC(50)) with plant-derived molluscicides Annona squamosa, acetogenins, Argemone mexicana seed and protopine, in combination (1 + 5) with MGK-264 (ENT 8184) or piperonyl butoxide on the reproduction of Lymnaea acuminata has been studied. The plant-derived molluscicides and their active molluscicidal components, protopine and acetogenins, in combination with ENT 8184 or piperonyl butoxide caused a significant reduction in the fecundity, hatchability and survival of young snails. Combination of A squamosa seed powder with piperonyl butoxide was very effective as it caused a complete arrest of snail fecundity within 24 h of treatment. Removal of the snails to fresh water after the 96-h treatments caused a significant recovery in the fecundity of L acuminata.     

Selective inhibition of the metabolism of diazinon and diazoxon in vitro by piperonyl butoxide,NIA 16824, and 1-(2-isopropylphenyl)imidazole

Several pesticide synergists known to be mixed-function oxidase inhibitors were found to inhibit the in vitro metabolism of diazinon by mouse liver microsomes. Piperonyl butoxide and NIA 16824 (O-isobutyl-O-propargyl phenylphosphonate) inhibit all oxidative reactions of diazinon to the same extent. In contrast, 1-(2-isopropylphenyl)imidazole selectively inhibits oxidative dearylation and thiophosphate to phosphate conversion without significant effect on ring side chain hydroxylation. This selectivity suggests that two different mechanisms of oxidative detoxification may be operating, mechanisms which may involve either two cytochrome P-450s or two different binding sites on the same cytochrome.     

The response of pyriproxyfen-resistant and susceptible Bemisia tabaci Genn (Homoptera: Aleyrodidae) to pyriproxyfen and fenoxycarb alone and in combination with piperonyl butoxide

Pyriproxyfen was effective against susceptible Bemisia tabaci eggs at a LC₅₀ of 0.003 mg litre⁻¹ and against nymphs at 0.02 mg litre⁻¹. In comparison, eggs of a laboratory selected, pyriproxyfen-resistant B tabaci strain, originating in an Israeli greenhouse, exhibited 6500-fold resistance and nymphs exhibited 1100-fold resistance. Eggs and nymphs of a strain from an Israeli sunflower field exhibited 450 and 210-fold resistance in comparison to the susceptible standard. Fenoxycarb was generally less effective than pyriproxyfen against B tabaci eggs and nymphs but was unaffected by pyriproxyfen resistance. Piperonyl butoxide (PB) was antagonistic to pyriproxyfen, and this increased with increasing pyriproxyfen resistance. PB had no effect on the toxicity of fenoxycarb. Collectively, these data imply that the modes of action of pyriproxyfen and fenoxycarb are distinct, despite the structural similarities of these molecules. Possible reasons for the antagonism of PB against pyriproxyfen are discussed. © 1999 Society of Chemical Industry     

The effect of a piperonyl butoxide/tau-fluvalinate mixture on pollen beetle (Meligethes aeneus) and honey bees (Apis mellifera)

BACKGROUND: Previous work has characterised pyrethroid resistance in pollen beetle (Meligethes aeneus F.) as principally an oxidative mechanism. Piperonyl butoxide (PBO) can synergise this resistance in the field, but its effects on the honey bee are thought to be unacceptable. RESULTS: A field trial in Poland was conducted to show that a mixture of PBO and tau‐fluvalinate at the registered rate gave increased and longer‐lasting control of resistant pollen beetle. Four days after spraying with tau‐fluvalinate, only 20% of pollen beetles were controlled, compared with 70% if the tau‐fluvalinate/PBO mixture was used. No detriment to honey bee health was observed using the same mixture. CONCLUSIONS: PBO, if used in conjunction with a pyrethroid of relatively low bee toxicity, can successfully overcome pyrethroid resistance in pollen beetle without incurring an increased loss of honey bees, even if they are present at the time of spraying. Copyright © 2012 Society of Chemical Industry     

Involvement of esterases in diazinon resistance and biphasic effects of piperonyl butoxide on diazinon toxicity to Haematobia irritans irritans (Diptera: Muscidae)

Resistance to insecticides remains a major problem for the successful control of the horn fly, Haematobia irritans irritans (L.), one of the most important pests of cattle in many countries including the United States. The organophosphate (OP) insecticide diazinon has been used to control pyrethroid-resistant populations of the horn fly. There are only a few reported cases of horn fly resistance to diazinon in the United States and Mexico. Piperonyl butoxide (PBO) has been used successfully as a synergist of pyrethroid insecticides to control horn flies. PBO-synergized diazinon products are also available for horn fly control in the United States, although PBO is known to inhibit the bio-activation of certain OP insecticides including diazinon. A study was conducted to evaluate the effect of PBO on diazinon toxicity to horn flies using a filter paper bioassay technique. These bioassays in both the susceptible and diazinon-resistant horn fly strains revealed a biphasic effect of PBO on diazinon toxicity to horn flies. PBO inhibited diazinon toxicity when the PBO concentration used was high (5%), and no effect was observed when PBO concentration was intermediate (2%). However, at low concentrations (1% and lower), PBO significantly synergized diazinon toxicity. We demonstrated that enhanced esterase activity was associated with survivability of horn flies exposed to diazinon alone. PBO has been shown to inhibit esterase activity in other insect species. However, results of biochemical assays with esterases from this study suggest that PBO did not have significant effect on the overall esterase activity in the horn fly. The observed synergistic effect of PBO at lower concentrations on diazinon toxicity to horn flies could not be explained by reduced esterase activity due to PBO inhibition. It is likely that PBO synergized diazinon toxicity at lower concentrations by facilitating penetration of diazinon through the cuticle and/or inhibiting the oxidative detoxification of diazinon, and reduced diazinon toxicity at high PBO concentration by inhibiting the bio-activation of diazinon.     

Effect of pretreatment with piperonyl butoxide on pyrethroid efficacy against insecticide-resistant Helicoverpa armigera (Lepidoptera: Noctuidae) and Bemisia tabaci (Sternorrhyncha: Aleyrodidae)

Pyrethroid resistance in B-type Bemisia tabaci Gennadius and Australian Helicoverpa armigera Hübner field populations is primarily conferred by esterase isoenzymes which metabolise and sequester pyrethroid insecticides. It has been shown previously that pyrethroid resistance-associated esterases in H. armigera are inhibited by the insecticide synergist piperonyl butoxide (PBO) over a 22-h period. It is demonstrated here that similar inhibition can be obtained against B-type B. tabaci. Small-scale field trials showed excellent levels of pyrethroid control when insects were pretreated with PBO and then dosed with pyrethroid during the time of maximum esterase inhibition. These results demonstrate that PBO can restore pyrethroid efficacy in the field against both B-type B. tabaci and resistant H. armigera.     

The interactions between piperonyl butoxide and E4, a resistance‐associated esterase from the peach‐potato aphid,Myzus persicae Sulzer (Hemiptera: Aphididae)

BACKGROUND: It has been reported previously that piperonyl butoxide (PBO) can inhibit both P450 and esterase activity. Although the method by which PBO combines with cytochrome P450 has been identified, the way in which it acts as an esterase inhibitor has not been established. This paper characterises the interactions between PBO and the resistance‐associated esterase in Myzus persicae, E4. RESULTS: After incubation with PBO/analogues, hydrolysis of 1‐naphthyl acetate by E4 is increased, but sequestration of azamethiphos is reduced. Rudimentary in silico modelling suggests PBO docks at the lip of the aromatic gorge. CONCLUSIONS: PBO binds with E4 to accelerate small substrates to the active‐site triad, while acting as a blockade to larger, insecticidal molecules. Structure–activity studies with analogues of PBO also reveal the essential chemical moieties present in the molecule. © 2012 Society of Chemical Industry