Biorational substitution of piperonyl butoxide in organic production: effectiveness of vegetable oils as synergists for pyrethrums.

Piperonyl butoxide is a semi-synthetic synergist for natural pyrethrum and synthetic pyrethroid insecticides in phytochemicals and biocides. As such it is used in large quantities for crop treatments, stored grain protection, disinfestation of grain storage facilities and indoor uses. Piperonyl butoxide is consequently a regular contaminant in stored grains, and subsequently in corresponding cereal food products and meat via feed uses. Therefore it is regularly monitored and its MRL is ongoing a reassessment. It is also considered as a possible human carcinogen and a suspected endocrine disruptor. For all these reasons and considerations most of the countries have already banned its use in Organic Farming as France in 2017. Thus, ecological substitution of with biorational and sustainable solutions is required. Vegetable oils have been described as exhibiting similar potency and synergistic effects. We have reviewed the literature and have proceeded to ecotoxicological efficacy tests in order to determine the best and most durable substitution candidates. Sesame and rape seed oil were determined to be the most efficient.

The interactions of piperonyl butoxide and analogues with the metabolic enzymes FE4 and CYP6CY3 of the green peach aphid Myzus persicae (Hemiptera: Aphididae).

BACKGROUND: Piperonyl butoxide (PBO) is a well-known insecticide synergist capable of interacting with phase 1 metabolic enzymes, specifically esterases and cytochrome P450s. In this study, structure-activity relationship analyses were used to characterise the interaction of around 30 analogues of PBO with the esterase FE4 and the P450 CYP6CY3 from insecticide-resistant Myzus persicae (Sulzer), in order to predict the synthesis of more potent inhibitors. RESULTS: Enzyme inhibition studies were performed against esterase and oxidase activities and, together with in silico modelling, key activity determinants of the analogues were identified and optimised. Novel analogues were then designed and synthesised, some of which showed greater inhibition against both enzymatic systems: specifically, dihydrobenzofuran moieties containing an alkynyl side chain and a butyl side chain against FE4, and benzodioxole derivatives with a propyl/butyl side chain and an alkynyl ether moiety for CYP6CY3. CONCLUSIONS: In vitro assays identified potential candidate synergists with high inhibitory potency. The in vivo confirmation of such results will allow consideration for a possible use in agriculture. © 2016 Society of Chemical Industry.

Effects of relative humidity and substrate on the spatial association between glyphosate and ethoxylated seed oil adjuvants in the dried deposits of sessile droplets.

BACKGROUND: In recent years, several studies have shown the impact of adjuvants on the characteristics of herbicide deposits on leaf surfaces. Until now, most studies have addressed the distribution of active ingredients (AIs), whereas few experiments have focused on the location of the adjuvants. The objective of this study was a systematic examination of the particle distribution profile of both the AI (glyphosate, Gly) and the adjuvants after the application of sessile microdroplets on hydrophobic (Teflon) and hydrophilic (glass and aluminium) model surfaces. RESULTS: The association degree (AD) was surface dependent and specific for the tested adjuvants. In general, the rather hydrophobic adjuvant RSO 5 showed decreasing AD with Gly at increasing relative humidity (RH) levels. The rather hydrophilic RSO 60 adjuvant displayed higher AD between the compounds at a higher RH. A high concentration of the adjuvant reduced the AD for both of the RSO adjuvants evaluated. CONCLUSION: The combination of surface properties, the type of adjuvant and the relative humidity determines the degree of association between Gly and the adjuvants. The present results suggest that the interaction between the AI and an adjuvant determines whether spatial separation occurs, whereas physical processes (e.g. capillary particle movement, inward and outward Marangoni flows and the evaporation rate) are decisive for the extent of the separation. Coffee-ring structures were formed exclusively with the adjuvant+Gly mixtures, whereas Gly alone formed either one big deposit or several small islands distributed within the droplet footprint.

[Antimitotic activity of new 2,6-dinitroaniline derivatives and their synergistic activity in compositions with graminicides].

Shown antimicrotrubules activity of new 2,6-dinitroaniline compounds. Investigated their ability on apoptotic processes in a plant cell when used as a composition with inhibitors of acetyl-CoA carboxylase.

Synthesis of novel vanillin derivatives containing isothiazole moieties and its synergistic effect in mixtures with insecticides.

Reaction between 4-formyl-2-methoxyphenyl 4,5-dichloroisothiazole-3-carboxylate with various aromatic amines led to azomethins 2-7 formation. By treatment of azomethins 2-7 with sodium triacetoxyborohydride corresponding amines 8-11 were obtained. During the bioassays of new vanillin derivatives in mixtures with insecticides remarkable synergetic effect was discovered.

Manduca sexta (Lepidoptera: Sphingidae) cadherin fragments function as synergists for Cry1A and Cry1C Bacillus thuringiensis toxins against noctuid moths Helicoverpa zea, Agrotis ipsilon and Spodoptera exigua.

BACKGROUND: Specific Bacillus thuringiensis Berliner (Bt) toxins are effective against a narrow spectrum of species. While specificity is an advantage for limiting adverse effects on non-target organisms, it is also the primary drawback of Bt's application for controlling multiple pest species in agriculture, forestry and other areas. Recently, it was reported that a small toxin-binding fragment of Manduca sexta (Joh.) cadherin acts as a synergist of Bt toxins to M. sexta, Heliothis virescens F. and Helicoverpa zea (Boddie). These insects are quite susceptible to the Cry1A toxins. The first aim of the present study was to determine if longer-sized fragments of M. sexta cadherin differed in the level of toxin enhancement. The second aim was to examine enhancement of Bt toxins against relatively Bt-tolerant insects Agrotis ipsilon (Hufn.) and Spodoptera exigua (Hübner). RESULTS: Cadherin fragments longer than previously reported had improved synergistic properties. Significant enhancement of Bt Cry1A toxins against A. ipsilon and S. exigua was found. A cadherin fragment also increased Cry1C toxicity to S. exigua. CONCLUSIONS: The commercial development of this synergist has the potential to widen the spectrum of Bt toxicity to other important agricultural lepidopteran insect pests and thus increase its usefulness in agriculture.

Carbamates synergize the toxicity of acrinathrin in resistant western flower thrips (Thysanoptera: Thripidae).

The insecticidal efficacy of mixtures of acrinathrin (pyrethroid) with carbamate fungicides (propamocarb, carbendazim, iprovalicarb, and diethofencarb) and insecticides (carbaryl, thiodicarb, pirimicarb, and oxamyl) was studied in a field strain of Frankliniella occidentalis (Pergande). The fungicide propamocarb and the insecticides pirimicarb and oxamyl were selected for further studies of their synergism action with more detailed bioassays. The method consisted of combining increasing concentrations of acrinathrin with a constant sublethal rate of the carbamate as synergist. These three carbamates did not show synergism to acrinathrin in a laboratory insecticide-susceptible strain, but they did in two field strains, with higher acrinathrin resistance corresponding to higher synergism. Carbamates such as pirimicarb, oxamyl, and propamocarb could be practical candidates for field use as synergists, even against other pests with metabolic resistance.

The influence of the extensional viscosity of very low concentrations of high molecular mass water-soluble polymers on atomisation and droplet impact.

BACKGROUND: Water-soluble polymers are increasingly added to herbicide and pesticide formulations at very low concentrations (100-1000 mg L(-1)) in order to control the spray characteristics, notably to reduce spray drift and influence droplet bounce. The incorporation of polymeric adjuvants improves the efficacy of the spray solutions, thus enabling crop growers to maximise the performance of agrochemical sprays at lower dose rates of active ingredient. It is important to establish a fundamental understanding of how polymers influence the processes involved in droplet deposition. RESULTS: The shear and extensional viscosities of a series of high molecular mass (M(w)) poly(acrylamides) (M(w) approximately 10(6)-10(7)) have been determined at very low concentrations (100-1000 mg L(-1)). The polymer solutions demonstrated typical shear thinning characteristics under shear, and strain hardening behaviour under extension above a critical strain rate. The presence of the polymers was shown to increase the size of droplets produced in atomisation using an agricultural spray nozzle, as measured by laser diffraction. This was attributed to the increase in the extensional viscosity at the strain rates generated under pressure in the spray nozzle and was a function of both polymer concentration and M(w). In addition, the presence of polymer was found to have a significant influence on droplet bounce. CONCLUSIONS: The presence of very low concentrations of high molecular mass poly(acrylamides) significantly influences the size of droplets formed on atomisation and subsequent bounce characteristics. Large extensional viscosities generated above a critical strain rate are responsible for both processes.

Ethoxylated rapeseed oil derivatives as non-ionic adjuvants for glyphosate.

In a study aimed at finding environmentally benign adjuvants for glyphosate, ethoxylates of rapeseed oil and of methylated rapeseed oil were synthesized, with ethylene oxide (EO) content up to 40 and 8 respectively. They had less influence on spray retention by barley shoots than ethoxylated (15 EO) tallow amine (ETA). At 10 g L(-1), ethoxylated rapeseed oil with 30 or 40 EO and ethoxylated methylated rapeseed oil with 6 or 8 EO promoted glyphosate uptake by barley leaves to a greater extent than ETA at the same concentration. However, uptake rates were similar when the concentration was lowered to 2.8 and 3.1 g L(-1) for rapeseed oil derivatives and ETA respectively. In the case of ethoxylated methylated rapeseed oil with 8 EO (MeOil-8), glyphosate uptake increased when MeOil-8 concentration was raised from 5 to 10 g L(-1). In bioassays under controlled conditions, ethoxylated rapeseed oil with 40 EO (Oil-40) and MeOil-8 were slightly less effective than ETA in favouring the efficacy of glyphosate on barley. The same was found on ryegrass. However, both rapeseed oil derivatives compared well with glyphosate formulants such as ethoxylated diethylamine and alkyl ethoxy phosphate. In one field experiment, the efficacy of glyphosate in the presence of Oil-40, MeOil-8 or ETA was comparable with that of a commercial formulation. In another trial, MeOil-8 was as effective as ETA, but Oil-40 performed less well. It is concluded that ethoxylates of rapeseed oil and of methylated rapeseed oil are a promising chemistry for glyphosate adjuvants, provided that their ethylene oxide content is high.

Linear alcohol ethoxylates: insecticidal and synergistic effects on German cockroaches (Blattodea: Blattellidae) and other insects.

Sixteen linear ethoxylated alcohol surfactants (AEOs) were studied to determine their contact insecticidal activity to adult German cockroaches, Blattella germanica (L.) (Blattodea: Blattellidae). Within groups of AEOs of equal carbon chain length, insecticidal activity, measured as LT50 values (in minutes) and 24-h mortality after treatment, was inversely related to the amount of ethoxylation. There was a highly significant negative relationship between the hydrophile-lipophile balance (HLB) value of the AEO and contact toxicity. The AEO with the lowest HLB value, Tomadol 23-1 (HLB = 3.7), produced the greatest 24-h cockroach mortality. The contact activity of Tomadol 23-1 was evaluated against a wide range of other insect species. Most species were killed within 24 h by direct exposure (1-4 microl of a 50% ethanol solution) to Tomadol 23-1 or by spray exposure to an aqueous solution. Tomadol 23-1, at a sublethal concentration, was tested in combination with representative members of the carbamate, nicotinoid, organophosphate, pyrethrum, pyrethroid, and pyrrole insecticide classes. Significant synergism was demonstrated in combinations of Tomadol 23-1 and chlorfenapyr, clothianidin, imidacloprid, thiamethoxam, and pyrethrum. Tomadol 23-1 significantly reduced the insecticidal activity of propoxur, suggesting antagonism. The insecticidal activity of Tomadol 23-1 was synergized by coapplication with a sublethal amount of piperonyl butoxide, indicating the involvement of cytochrome P450 microsomal monooxygenases in insect metabolism of AEO surfactants.

Mode of action of Bacillus thuringiensis Cry and Cyt toxins and their potential for insect control.

Bacillus thuringiensis Crystal (Cry) and Cytolitic (Cyt) protein families are a diverse group of proteins with activity against insects of different orders--Lepidoptera, Coleoptera, Diptera and also against other invertebrates such as nematodes. Their primary action is to lyse midgut epithelial cells by inserting into the target membrane and forming pores. Among this group of proteins, members of the 3-Domain Cry family are used worldwide for insect control, and their mode of action has been characterized in some detail. Phylogenetic analyses established that the diversity of the 3-Domain Cry family evolved by the independent evolution of the three domains and by swapping of domain III among toxins. Like other pore-forming toxins (PFT) that affect mammals, Cry toxins interact with specific receptors located on the host cell surface and are activated by host proteases following receptor binding resulting in the formation of a pre-pore oligomeric structure that is insertion competent. In contrast, Cyt toxins directly interact with membrane lipids and insert into the membrane. Recent evidence suggests that Cyt synergize or overcome resistance to mosquitocidal-Cry proteins by functioning as a Cry-membrane bound receptor. In this review we summarize recent findings on the mode of action of Cry and Cyt toxins, and compare them to the mode of action of other bacterial PFT. Also, we discuss their use in the control of agricultural insect pests and insect vectors of human diseases.

Pyrethrins and piperonyl butoxide adsorption to soil organic matter.

The adsorption and mobility of pyrethrins (Pys), the major insecticidal components obtained from the pyrethrum daisy Tanacetum cinerariifolium, and piperonyl butoxide (PBO), a pyrethrum synergist, were determined in soil using batch-equilibrium and reverse-phase thin-layer chromatographic techniques. Two soil management practices were used, soil mixed with yard waste compost (COM) at 50 t acre(-1) on dry weight basis and no-mulch (NM) bare soil. Adsorption isotherm experiments were carried out using known concentrations of Pys (Py-I and Py-II) and PBO mixed with known amounts of COM or NM soil at constant temperature and pressure until equilibrium was attained. Pys and PBO in soil extracts were purified and concentrated using solid-phase extraction cartridges containing C18-octadecyl bonded silica. Pys and PBO residues were quantified using a high-performance liquid chromatograph equipped with a UV detector. Adsorption studies showed that compost amended soil adsorbed more Pys and PBO than native (NM) soil. Py-I adsorption was greater than Py-II and PBO. Adsorption of Pys and PBO to humic and fulvic acids was also studied by reverse-phase thin layer chromatography (RPTLC). Results indicated that humic acid, a significant component of organic matter, reduced Pys and PBO mobility. Pys and PBO mobility decreased as the concentration of humic acid in the mobile phase increased.

Influence of suspended solids on acute toxicity of carbofuran to Daphnia magna: I. Interactive effects.

This study explored the effects on Daphnia magna from exposure to the pesticide carbofuran in combination with stress from suspended solids exposure. Our objective was to assess whether suspended solids affects the toxicodynamic response of D. magna to carbofuran. A series of laboratory experiments was performed where animals were exposed to carbofuran concentrations ranging from 0 to 160 microg/l in combination with suspended solids concentrations ranging from 0 to 10000 mg/l. In the absence of suspended solids, effects of carbofuran were dose dependent and resulted in an EC(50) of 92 microg/l. Exposure to suspended solids, up to extreme levels that may be encountered in the environment and in the absence of carbofuran, showed no measurable toxicity. When D. magna were exposed to a constant carbofuran concentration, the numbers of affected organisms increased with increasing suspended solids concentrations. At a suspended solids concentration of 1000 mg/l, the EC(50) for carbofuran was reduced by half to 45 microg/l. The relationship between the toxicity of carbofuran (microg/l) and the concentration of suspended solids (mg/l) can be described with the following equation: carbofuran EC(50)=72 exp(-0.00014 [suspended solids]). An analysis of the data indicates that this relationship is consistent with a potentiated toxicity mechanism rather than an additive model.

Modulators of membrane drug transporters potentiate the activity of the DMI fungicide oxpoconazole against Botrytis cinerea.

Modulators known to reduce multidrug resistance in tumour cells were tested for their potency to synergize the fungitoxic activity of the fungicide oxpoconazole, a sterol demethylation inhibitor (DMI), against Botrytis cinerea Pers. Chlorpromazine, a phenothiazine compound known as a calmodulin antagonist, appeared the most potent compound. Tacrolimus, a macrolide compound with immunosuppressive activity, was also active. The synergism of chlorpromazine negatively correlated with the sensitivity of the parent strain and mutants of B. cinerea. The synergism was highest in a mutant that overexpressed the ATP-binding cassette transporter BcatrD, known to transport DMI fungicides such as oxpoconazole. The synergism of chlorpromazine positively correlated with its potency to enhance the accumulation of oxpoconazole in BcatrD mutants. These results indicate that chlorpromazine is a modulator of BcatrD activity in B. cinerea and suggest that mixtures of DMI fungicides with modulators may represent a perspective for the development of new resistance management strategies.

Ethoxylated rapeseed oil derivatives as novel adjuvants for herbicides.

Ethoxylates of rapeseed oil and of methylated rapeseed oil were synthesized and tested as adjuvants for 2,4-D and phenmedipham. Provided they had less than 6 units of ethylene oxide (EO), 1.0 to 10 g litre(-1) ethoxylates in water induced droplet spreading on barley leaves. In an acetone-based medium all derivatives strongly promoted the foliar uptake of 2,4-D, with no clear influence of the ethoxylation degree. In the same medium there was a negative influence of ethoxylate chain length on the foliar uptake of phenmedipham. In a water-based medium, phenmedipham applied with rapeseed oil emulsified with ethoxylated (20 EO) rapeseed oil displayed uptake rates close to a commercial preparation. The same was true for phenmedipham applied with ethoxylated (2 EO) methylated rapeseed oil. In bioassays, phenmedipham prepared with methylated rapeseed oil emulsified with ethoxylated (20 EO) rapeseed oil was as efficacious on barley as a commercial formulation. The same was true for phenmedipham prepared with ethoxylated (2 EO) methylated rapeseed oil. However, neither rapeseed oil nor methylated rapeseed oil emulsified with ethoxylated (2 EO) methylated rapeseed oil conferred good efficacy to phenmedipham. Hence, ethoxylated rapeseed oil derivatives are promising adjuvants or formulants for herbicides.

On the mechanism of selectivity of the corn herbicide BAS 662H: a combination of the novel auxin transport inhibitor diflufenzopyr and the auxin herbicide dicamba.

BAS 662H, a 1:2.5 combination of the semicarbazone-type auxin transport inhibitor diflufenzopyr and the auxin herbicide dicamba, is used as a post-emergence herbicide in corn. The combination has been observed to provide more effective broadleaf weed control and improved tolerance in corn than typical rates of dicamba used alone. In order to analyze this phenomenon, the uptake, translocation, metabolism and action of both compounds, applied alone and in combination, were investigated in Amaranthus retroflexus L, Galium aparine L and corn (Zea mays L). When plants at the third-leaf stage were foliarly treated with diflufenzopyr and dicamba equivalent to field rates of 100 and 250 gha-1, respectively, diflufenzopyr synergistically increased dicamba-induced 1-aminocyclopropane-1-carboxylic acid (ACC) synthase activity and ethylene formation in G aparine and even more in A retroflexus, followed by accumulations of (+)-abscisic acid (ABA) in the shoot tissue within 20 h. This correlated with subsequent growth inhibition, hydrogen peroxide overproduction and progressive tissue damage. Diflufenzopyr also enhanced the activity of other auxin herbicides, such as quinclorac and picloram, and of the synthetic auxin, 1-naphthaleneacetic acid. After foliar and root application of [14C]diflufenzopyr, alone or as BAS 662H, considerably lower tissue concentrations and systemic translocation of radioactivity beyond treated plant parts were found in corn, compared to G aparine and particularly A retroflexus. Furthermore, diflufenzopyr decreased foliar uptake of [14C]dicamba by c 50% selectively in corn, compared to the treatment alone. Metabolism of [14C]diflufenzopyr was more rapid in corn than in the weed species. In combination, the two compounds had no mutual effect on their metabolic degradation. In BAS 662H, diflufenzopyr synergizes the herbicidal activity of dicamba in sensitive weed species. In corn this effect is prevented by a more rapid metabolism of diflufenzopyr, coupled with lower uptake and translocation. Selectivity of BAS 662H is additionally favoured by a higher crop tolerance to dicamba because of reduced foliar uptake of this herbicide in corn under the influence of diflufenzopyr.

Developments in adjuvant use for agrochemicals.

Adjuvants can improve the targeting of pesticides and nutrients. During the last thirty years, the use of adjuvants has become a useful tool for optimising the efficacy of pesticides. In the USA volumes of approximately 110 ML oil and 20 ML surfactant are used per year. For several reasons, the yearly volume for oils and surfactants in Europe is much lower, being approximately 10 ML per year for oils and a similar amount for surfactants. The red line in the developments is a fine-tuning between composition of adjuvants and their function plus effect in a certain application. This means that knowledge-based development of adjuvants more than the "spray and pray" approach will gain importance. This paper describes in a nutshell the different chemistries and possible functions of adjuvants. Recent developments are presented regarding adjuvants for glyphosate, waxes, alkoxylated triglycerides, calcium nitrate and adjuvant influence on drift.

The effect of adjuvants on atomisation of pesticides.

Four surfactants Tween 20, Agral 90, Silwet L77 and Break Thru, commonly used in the formulations of agricultural products, were evaluated on their spray performance and dynamic surface tension. In a spray test the Dv 50 (micron) or the Volume Median Diameter and the percentage of droplets with diameter below 100 microns (drift sensitive droplets), were measured for different kind of nozzles varying from the classical flat fan up to the low drift nozzles. The spectra changed considerably when different kind of nozzles and different kind of surfactants were used, the concentration effect was less important. The dynamic tension of the different surfactant solutions could not always explain the changes in droplet spectrum.

Comparative evaluation of new synergists containing a butynyl-type synergophore group and piperonyl butoxide derivatives.

Cross-substituted derivatives of piperonyl butoxide (PBO) and MB-599 (proposed common name: verbutin) were synthesized and investigated as carbofuran and permethrin synergists against housefly, Musca domestica L. The majority of PBO and MB-599 derivatives were significantly more potent synergists for carbofuran than for permethrin. PBO, the most important representative of this series was not the most potent synergist for carbofuran or for permethrin. Cleavage of the methylenedioxy ring of methylenedioxyphenyl (MDP) polyether compounds resulted in complete loss of synergistic activity with both insecticides, but it could be restored or even improved by incorporating an alkynyl ether moiety into the molecule. The improved synergistic activity was found to be closely associated with the 2-butynyloxymethyl side-chain, suggesting that this can be regarded as a characteristic synergophore group. MB-599, one of the most promising compounds bearing this group showed considerably higher activity with carbofuran (synergist ratio, SR = 37.8) than with PBO (SR = 6.4). There was no significant difference between synergistic activities of MB-599 (SR = 4.6) and PBO (SR = 4) for permethrin.