Ergosterol Biosynthesis-inhibiting Fungicides Research Articles

Evaluation of cytotoxic and genotoxic activity of fungicide formulation Tango® Super in bovine lymphocytes

Tango® Super is a two-compound fungicide formulation widely employed in grain protection. However, details of Tango® Super effects on cell cultures have not been fully investigated. In this study, bovine lymphocytes were exposed to a concentration range 0.5; 1.5; 3; 6; and 15 μg mL−1 for 4 h to assess the cytotoxicity and genotoxicity of the fungicide. Our experiments revealed that this fungicide treatment reduced cell viability, decreased cell proliferation and provoked apoptotic cell death. Cell cycle analysis showed predominant accumulation of cells in the G0/G1 phase of the cell cycle. The fungicide was able to induce mitochondrial superoxide production accompanied by elevated levels of carbonylated proteins and changes in the lipid membrane composition. The fungicide did not induce micronuclei production, but stimulated both DNA double-strand breaks and the formation of p53 binding protein, which is accumulated during the DNA repair process at the site of double-strand breaks. Based on the obtained data we suppose that the fungicide-induced DNA damage is the result of oxidative stress, which may contribute to higher occurrence of apoptotic cell death. Because ergosterol biosynthesis-inhibiting fungicides are widely used in agriculture to ensure higher crop yields and may cause health impairment of animals and humans, there is a need for further testing to elucidate their potential genotoxic effects using in vivo and/or in vitro systems.

TOXICITY OF SOME INSECTICIDES AND THEIR MIXTURES WITH ERGISTROL BIOSYNTHESIS INHIBITING FUNGICIDES AGAINST THE 2ND INSTAR LARVAE OF SPODOPTERA LITTORALIS (BOISD)

The toxicity of organophosphorus insecticide (profenofos), pyrethroid insecticide (esfenvalirate), insect growth regulators, (flufenoxuron) and biocide as natural products (spinosad) increased when mixed with the butylated hydroxyanisol (BHA) and ergosterol biosynthesis inhibiting (EBI) fungicides to 2nd instar larvae of Spodoptera littoralis. Present study was carried out by feeding 2nd instar larvae on castor bean leaves treated with different concentrations of profenofos, esfenvalirate, flufenoxuron and spinosad either alone or in mixtures with BHA, EBI fungicide or IGR. Interestingly, these BHA and EBI did not kill the larvae at concentration up to 100 ppm, moreover 20 ppm of each BHA or EBI fungicide with concentrations of the insecticides increased the toxicity of these insecticides. Also, all data indicated that the calculated LC50 of the insecticides alone were higher than the insecticides and BHA, EBI fungicides or IGR. For instance, the LC50 of profenofos alone was 1.90 ppm, decreased to 0.08, 0.20, 0.24 and 0.22 ppm when mixed with BHA, difenoconazol, penconazol and flufenoxuron respectivily. Also, the insecticidal action increased by 23.75, 9.5, 7.91 and 8.63 folds. The LC50 values decreased when esfenvalirate mixed with BHA, difenoconazol, penconazol and flufenoxuron reached 0.32, 0.21, 0.28 and 0.33 ppm compared with 1.58 ppm when esfenvalirate used alone. Also, the insecticidal action increased by 4.93, 7.52, 5.64 and 4.78 folds when mixed with the mentioned BHA, EBI fungicides or the IGR respectively. Concerning flufenoxuron LC50 values alone was 1.83 decreased to 0.12, 0.19 and 0.22 ppm when mixed with BHA, difenoconazol, penconazol and flufenoxuron respectively, insecticidal action increased by 15.25, 9.63 and 8.31 folds respectively. LC50 values of spinosad was 1.44 ppm when used alone, decreased to 0.21, 0.21, 0.25 and 0.20 ppm when was mixed with BHA, difenoconazol, penconazol and flufenoxuron respectively, insecticidal action was increased by 6.85, 6.85, 5.76 and 7.2 folds respectively. These results suggested that the antioxidant butylated hydroxyanisol (BHA), ergosterol biosynthesis inhibiting (EBI) fungicides and the IGRs enhanced the insecticidal activity of profenofos, esfenvalirate and spinosad against 2nd instar S.littoralis.

살균제 살포횟수 감소를 위한 딸기 탄저병 방제프로그램

The effect of various fungicides on anthracnose of strawberry, caused by Colletotrichum gloeosporioides, was determined in vitro, and in greenhouse and field trials. The values of benomyl were clearly different between two sensitive and resistant groups of isolates. Iminoctadine tris had lower values than mancozeb and propineb as protective fungicides and the response of mancozeb, propineb and azoxystrobin was variable depending on the isolate. In the greenhouse, pre- and post- inoculation fungicide applications significantly reduced disease compared to the non-treated control. Propineb, mancozeb and azoxystrobin were effective in controlling the disease when applied prior to inoculation. Metconazole and prochloraz-Mn treatments as ergosterol biosynthesis-inhibiting fungicides had the lowest incidence of anthracnose. In the nursery field trials in 2009 and 2010, the reduced fungicide spray program provided similar levels of disease control compared to the calendar-based applications with captan. A reduced spray program based on efficacious fungicides such as prochloraz-Mn will be useful for strawberry growers and provide more options for controlling anthracnose in Korea.

Pesticide cocktails can interact synergistically on aquatic crustaceans

The ergosterol biosynthesis-inhibiting (EBI) fungicide prochloraz can enhance the effect of other pesticides in a range of animal species. Approximately 50% of the fungicides used in Denmark are EBI fungicides. Hence, if they all have synergising potential, a risk assessment of pesticide mixtures based on additivity might not suffice. This study investigates the synergising potential of six different EBI fungicides representing the imidazoles (prochloraz), the triazoles (epoxiconazole, propiconazole and tebuconazole), the piperidines (fenpropidin) and the morpholines (fenpropimorph) together with the pyrethroid insecticide alpha-cypermethrin. Tests were made on the aquatic crustacean Daphnia magna. Mixtures of each of the fungicides were tested together with the insecticide both at a 50:50% effect mixture ratio and, subsequently, in a ray design including five mixture ratios. The results were tested against the concentration addition reference model using dose-response surface analyses. The results of the binary dose-response surface studies showed that mixtures with prochloraz increased toxicity up to 12-fold compared with what was expected using the reference model concentration addition (CA). Epoxiconazole and propiconazole enhanced toxicity up to six and sevenfold, respectively. Fenpropimorph showed antagonism, whilst mixtures with tebuconazole and fenpropidin did not deviate statistically from CA. Hence, it can be concluded that both imidazoles and some, but not all, triazoles can enhance the effect of a pyrethroid insecticide towards D. magna substantially. Epoxiconazole and propiconazole are often sprayed out together with pyrethroids in tank mixtures. The extent to which this might create unforeseen ecological problems is discussed.

SYNERGISM AMONG SOME INSECTICIDES AND ERGOSTEROL BIOSYNTHESIS INHIBITING FUNGICIDES AGAINST PECTINOPHORA GOSSYPIELLA (SAUND.)

The toxicity of organophosphorus insecticide chlorpyrifos, pyrethroid insecticide cypermethrin, insect growth regulators, chlorfluazuron and biocide as a natural products spinosad increased when mixed with the ergosterol biosynthesis inhibiting (EBI) fungicides to newly hatched larvae of Pectinophora gossypiella. This study was carried out by feeding newly hatched larvae on artificial diet treated with different concentrations of the tested compounds either alone or in mixtures with EBI fungicide or IGR. Interestingly, these fungicides did not kill the larvae up to 100 ppm, moreover 20 ppm of each EBI fungicide with concentrations of the insecticides increased the toxicity of these insecticides. Also, all data indicated that the calculated LC50 of the insecticides alone were higher than the insecticides and fungicides or IGR. For instance, chlorpyrephos at 6.25 ppm caused 90.0 % larval mortality and 100.0 % larval mortality when mixed with 20 ppm of each fungicides or 3 ppm when mixed with IGR. The LC50 of chlorpyrifos alone were higher than that of chlorpyrifos when mixed with EBI fungicides and chlorfluazuron as IGR. For example, chlorpyrifos had LC50 equal 2.89 ppm, but 0.88, 0.48, 0.26, 0.26, and 0.13 ppm when mixed with difenoconazol, tetraconazol, imazalil, fenarimol and chlorfluazuron respectively. Also, the insecticidal action increased by 3.2, 6.02, 14.45, 11.11, 22.23 folds when mixed with the latter fungicides or the insect growth regulators. Cypermethrin at 25 and 12.5 ppm resulted in 81.66 and 78.33 % larval mortality when used alone, while these concentrations caused 100.0% larval mortality when 20 ppm of each fungicide or 3 ppm of IGR added to these concentrations. The LC50 values decreased when cypermethrin mixed with EBI fungicides or IGR, the LC50 were 1.95, 0.85, 1.01, 0.65 and 1.5 ppm when mixed with difenoconazol, tetraconazol, imazalil, fenarimol and chlorfluazuron compared with 3.01 ppm when cypermethrin used alone. Also, the insecticidal action increased by 1.54, 3.45, 2.98, 4.63, and 2.01 folds when mixed with the mentioned fungicides or the IGR respectively. Chlorfluazuron at 6.5 ppm caused 86.66 % larval mortality after 72 hr post treatment but the same concentration caused 100 % larval mortality after 48 hr from treatments when mixed with the latter EBI fungicides. LC50 values were 0.61, 0.11, 0.36 and 0.29 ppm respectively, compared with 1.01 ppm when used alone, insecticidal action increased by 6.01, 9.18, 2.85 and 3.48 folds respectively. Spinosad at 7.5 ppm caused 85.0 % larval mortality but the same concentration induced 100.0 % larval mortality when mixed with imazalil and fenarimol as EBI fungicides or chlorfluazuron as IGR and caused 95.08 and 98.33 when mixed with both difenoconazol and tetraconazol as EBI fungicides. LC50 values were decreased to 0.51, 0.41, 0.76, 0.61 and 0.56 ppm when was mixed with difenoconazol, tetraconazol, imazalil, fenarimol and chlorfluazuron respectively, compared with 1.54 ppm when used alone, insecticidal action was increased by 3.08, 3.21, 1.97, 2.56, and 2.75 folds respectively. These results suggested that EBI fungicides and the IGRs enhanced the insecticidal activity of chlorpyrifos, cypermethrin and spinosad against the pink bollworm P. gossypiella.

다양한 작물로부터 분리한 탄저병균(Colletotrichum spp.)의 살균제에 대한 반응

This study has been conducted to investigate the responses of various isolates of four Colletotrichum species such as C. gloeosporioides, C acutatum, C. coccodes, and C. dematium isolated from infected tissues of several crops to fungicides such as carbendazim, carbendazim+diethofencarb, four protective fungicides, and three ergosterol biosynthesis-inhibiting (EBI) fungicides. All the isolates of C. acutatum showed values in a range of 0.001-3.040 against carbandazim, a benzimidazole fungicide. As for the response to carbendazim, the isolates of C. gloeosporioides obtained from pepper, apple, and strawberry were clearly divided into two groups, resistant or sensitive isolates. All the resistant isolates showed values above 1000 , whereas the sensitive isolates had lower values than 0.550 . The isolates of C. gloeosporioides exhibited a negative cross resistance between carbendazim and diethofencarb (a N-phenylcarbamate fungicide), but isolates of C. acutatum did not. Toward carbendazim, C. coccodes and C. dematium isolates showed a similar response to C. acutatum isolates and the sensitive isolates of C. gioeosporioides, respectively. As for response of Protective fungicides, all the isolates of C. acutatum showed a more resistant reaction than all the isolates of C. gloeosporioides. However, there was no difference among 4 species of Colletotrichum against EBI fungicides.

보호용 살균제와 ergosterol 생합성 저해 살균제에 대한 고추 탄저병균의 약제 반응

전국의 고추 재배지에서 1999년과 2002년에 채집한 병든 고추로부터 각각 130개와 258개의 고추 탄저병균을 분리한 후, 4종의 보호용 살균제와 3종의 ergosterol생합성 저해 살균제에 대한 균사 생장 저해 정도를 측정함으로서 살균제들에 대한 저항성 모니터링을 실시하였다. 1999년에 분리한 균주는 세 가지 보호용 살균제, 즉 dithianon, chlorothalonil 및 propineb에 대해서는 2002년의 균주보다 더 저항성을 보였다. 이에 반하여 다른 보호용 살균제인 iminoctadine에 대해서는 오히려 2002년의 균주가 더 저항성인 것으로 나타났다. 세 개의 ergosterol 생합성 저해(EBI) 살균제, 즉 tebuconazole, hexaconazole 및 prochloraz에 대해서는 2002년의 균주가 1999년의 균주보다 더 저항성이 컸으며, 2002년도의 균주들의 <TEX>$EC_{50}$</TEX> 값은 1999년 균주들보다 1.2배 내지 4.4배가 높았다 위의 살균제들에 대한 탄저병균의 반응을 보면, 채집한 지역 간에 저항성을 차이가 크게 나타나고 있었다. 단기간내에 충북에서 분리한 균주들은 채집한 시기가 늦어질수록, 고추의 생육 초기에 주로 많이 사용되는 보호용 살균제들에 대한 <TEX>$EC_{50}$</TEX>값은 감소하였다. 그러나 ergosterol 생합성 저해 살균제에 대한 균주들의 반응은 정해진 생육 기간 중에는 변화가 거의 없었다. In 1999 and 2002, 130 and 258 isolates of Colletotrichum spp. causing red pepper anthracnose were obtained from infected red pepper fruits, respectively. Their responses to 4 protective and 3 ergosterol biosynthesis-inhibiting(EBI) fungicides were investigated by observing their mycelial growth on PDA incorporated with different concentrations of each fungicide. The Colletotrichum isolates obtained in 1999 showed higher <TEX>$EC_{50}$</TEX> values than those isolated in 2002 against three protective fungicides such as dithianon, chlorothalonil, and propineb, whereas the response was reversed toward other protective fungicide, iminoctadine. On the other hand, the isolates of year 1999 were more resistant against three EBI fungicides such as tebuconazole, hexaconazole, and prochloraz than those of year 2002; the <TEX>$EC_{50}$</TEX> values of the former were 1.2-4.4 times higher than those of the latter, The responses of the Colletotrichum isolates toward protective and EBI fungicides were fluctuated according to regions, where the infected fruits were collected. On the other hand, the resis tance of Colletotrichum isolates to protective fungicides increased during monitoring from July to September, However, their responses towards EBI fungicides were not changed.

Effect of Application Timing of Ergosterol Biosynthesis-inhibiting Fungicides on the Suppression of Disease and Latent Infection of Apple White Rot Caused by Botryosphaeria dothidea

To examine the duration of post-infectional activity of ergosterol biosynthesis-inhibiting fungicides (EBIs) against Botryosphaeria dothidea, the cause of apple white rot, a series of experiments was conducted for 3 years at different times during the apple-growing season using apples infected through artificial inoculation or natural infection. Disease incidence at harvest was gradually reduced as the time of chemical application was delayed until early or mid-August, regardless of the time of infection. Latent infections, detected after storing the fruit at 25°C for 4 weeks were also reduced by late season applications, but the reduction was less than that observed on the fruit at harvest. From these results, apple white rot can be effectively controlled by a single application of EBIs around mid-August, after which time, infections no longer occur in Korea.

Effects of two ergosterol-inhibiting fungicides on soil ergosterol and microbial biomass

The effects of two ergosterol biosynthesis-inhibiting fungicides, epoxiconazole and triadimefon (at 2 and 20 ×, and 1 and 10 × field rate, respectively), and of straw amendment on ergosterol and microbial biomass C in a sandy loam soil, were investigated. Initial soil ergosterol and microbial biomass C contents were about 1.6 μg g −1 and 330 μg g −1 soil, respectively. Both concentrations of the fungicides decreased soil ergosterol content by about 30% after 7 days incubation in unamended soil, following which contents were broadly similar to the control soil. Microbial biomass C remained largely unaffected in the unamended soil, except for a temporary inhibition of about 12% caused by triadimefon after 13 days incubation. After amendment of the soil with wheat straw, the inhibition of ergosterol biosynthesis reappeared, ranging from 4 to 34%, with epoxiconazole having a greater effect than triadimefon, both compared to ergosterol biosynthesis in soils given straw without the biocides. This inhibition was also transient, but was longer-lasting than in the unamended soil. A decrease in soil microbial biomass C, ranging from 5 to 12%, also occurred, in contrast to the unamended treatments. This indicates that the fungicides were more active against the newly synthesized microbial biomass than ainst the original population. Soil ergosterol content was a more sensitive measure of pesticide side-effects than microbial biomass C, and could be a useful method in this respect.

Fungicides and the induction of avian CYPs Induction, suppression and inhibition of multiple hepatic cytochromes P450 isozymes in the male rat and bobwhite Quail (Colinus virginianus) by ergos terol biosynthesis inhibiting fungicides (EBIFs) MJJ Ronis, M Ingleman-Sundberg and TM Badger Biochemical Pharmacology, 1994; 48: 1953-1965

Fungicides and the induction of avian CYPs Induction, suppression and inhibition of multiple hepatic cytochromes P450 isozymes in the male rat and bobwhite Quail (Colinus virginianus) by ergos terol biosynthesis inhibiting fungicides (EBIFs) MJJ Ronis, M Ingleman-Sundberg and TM Badger Biochemical Pharmacology, 1994; 48: 1953-1965

Toxic Interactions Between Fungicides That Inhibit Ergosterol Biosynthesis and Phosphorothioate Insecticides in the Male Rat and Bobwhite Quail (Colinus virginianus)

The potential for toxic interactions between ergosterol biosynthesis-inhibiting fungicides (EBIFs), used in U.S. agriculture or clinically, and phosphorothioate insecticides was assessed in adult male rats and adult male bobwhite quail (Colinus virginianus) by measuring inhibition of plasma butyryl cholinesterase (BChE) following fungicide and insecticide treatment. Male Sprague-Dawley rats (300 g) were administered corn oil or the following EBIFs: propiconazole (400 mg/kg/day), vinclozolin (400 mg/kg/day), clotrimazole (100 mg/kg/day), or ketoconazole (100 mg/kg/day) for 3 days by oral gavage. Forty-eight hours following the final dose, a single bolus of parathion (0.4 mg/kg in corn oil) or malathion (150 mg/kg in corn oil) or corn oil alone was given po. The rats were terminated 12 hr following parathion or 4 hr following malathion dosing. Significant (p < 0.05) inhibition of BChE was observed with parathion and malathion only following clotrimazole treatment. In contrast, when a similar experiment was performed in bobwhite quail dosed with 12 mg/kg malathion following EBIF treatment, significant BChE inhibition was observed following treatment with vinclozolin or ketoconazole, but not with propiconazole or clotrimazole. Induction of cytochrome P450 in rat and quail liver by EBIFs was accompanied by enhanced oxidative desulfuration of malathion, parathion, and diazinon to toxic oxon products. Increased detoxication via oxidative dearylation/esterolytic clevage also occurred. However, while enhanced acute in vivo insecticide toxicity was observed in both species with a number of EBIF-phosphorothioate combinations, EBIF-induced oxidative activation of phosphorothioates by liver microsomes in vitro was not a good predictor of this effect.

Mechanism of Synergism between the Pyrethroid Insecticide λ-Cyhalothrin and the Imidazole Fungicide Prochloraz, in the Honeybee ( Apis mellifera L.)

Ergosterol biosynthesis-inhibiting fungicides have been found to synergize the toxicity of pyrethroid insecticides to the honeybee ( Apis mellifera L.). The mechanism by which the fungicide prochloraz enhances the toxicity of the pyrethroid insecticide λ-cyhalothrin was investigated. In vitro incubations with honeybee midguts were used to study the metabolism of [ 14C]λ-cyhalothrin. The principal metabolite was identified as 4-hydroxy-3-phenoxybenzyl alcohol (4′-OH-3-PBAlc) with small amounts of 3-phenoxybenzoic acid (3-PBAc). Both are products of ester bond cleavage, but microsomal oxidation was implicated in the formation of 4′-OH-3-PBAlc. After treating midguts with prochloraz, metabolism was predominantly to 3-PBAc, with little formation of 4′-OH-3-PBAlc, strongly indicating an inhibition of microsomal monooxygenase activity. In vivo investigations showed the major metabolic products of [ 14C]λ-cyhalothrin extracted from frass of treated honeybees were 4′-OH-3-PBAlc, 2′-hydroxy-3-phenoxybenzyl alcohol, and 4′-hydroxy-3-phenoxybenzoic acid. However, when bees were simultaneously dosed with prochloraz, there was an absence of metabolites detected in the frass of bees for 16 hr post-treatment Thus, prochloraz delayed the metabolism, detoxication, and excretion of λ-cyhalothrin by inhibition of microsomal oxidation, effectively enhancing the toxicity of the pyrethroid to the honeybee.

Induction, suppression and inhibition of multiple hepatic cytochrome P450 isozymes in the male rat and bobwhite quail ( Colinus virginianus) by ergosterol biosynthesis inhibiting fungicides (EBIFs)

Ergosterol biosynthesis inhibiting fungicides (EBIFs) have complex effects on the hepatic microsomal monooxygenase systems of vertebrate species, having been described as mixed inducers and inhibitors of cytochrome P450. In the current study, we examined the effects of two EBIFs in clinical use, clotrimazole and ketoconazole, and two agricultural EBIFs, propiconazole and vinclozolin, on hepatic monooxygenase activities and P450 apoprotein expression in the male Sprague-Dawley rat and the male bobwhite quail. EBIFs produced Type II binding spectra with hepatic microsomes from both species and were effective inhibitors of methoxyresorufin O-demethylase, an activity selective for P450 isozymes in gene family 1. However, the EBIFs varied widely in their effectiveness as inducers of P450 isozymes in gene families 1, 2, 3 and 4, both within the same species and between species. In the rat, clotrimazole was the most effective inducer, increasing expression of CYP 3A isozymes over 450-fold, CYP 2B1/2 30-fold and CYP 1A1/2 12-fold and suppressing expression of CYP 2C11 nearly 70%. By contrast, in the quail, clotrimazole was the least effective inducer. In quail, vinclozolin and propiconazole elevated total P450 content 10- and 7-hold, respectively. The induction response also appeared to be mixed, but in this case consisted of a 5-fold induction of P450s in gene family 1A, a 3-fold induction of P450s in gene family 3A and 4A, and induction of protein(s) from gene family 2, cross-reactive with antisera against rat CYP 2C11 and CYP 2A1. A protein that was cross-reactive with antibodies raised against rat CYP 2B1 was decreased with EBIF treatment. In conclusion, EBIFs have complex patterns of induction, suppression and inhibition of cytochrome P450 isozymes in both mammals and birds, which vary according to both the fungicide and the species.

Interactive effects between EBI fungicides (prochloraz, propiconazole and penconazole) and OP insecticides (dimethoate, chlorpyrifos, diazinon and malathion) in the hybrid red-legged partridge

The toxicokinetic interactions between the ergosterol-biosynthesis-inhibiting (EBI) fungicides prochloraz, propicon-azole, and penconazole and the organophosphorus (OP) insecticides dimethoate, chlorpyrifos, and diazinon have been studied in the hybrid red-legged partridge. The inhibition of serum butyrylcholinesterase (BuChE) activity provided a useful biochemical indicator of the generation of the toxic oxon metabolites of these OP insecticides. Birds pretreated with 180 mg/kg prochloraz tended to show a greater inhibition of serum BuChE activity at 1, 4, and 24 h following oral exposure to either of the OPs dimethoate (3 mg/kg) or chlorpyrifos (9 mg/kg) compared to birds pretreated with corn oil. Prochloraz-pretreated birds also showed a tendency toward an increased inhibition at 24 h following dosing with the OP diazinon (4.3 mg/kg) compared to corn oil controls. In the case of dimethoate, the inhibition of serum BuChE activity was significantly greater in treated birds than controls at 24 h. Birds pretreated with the EBI fungicide propiconazole (200 mg/kg) showed a similar inhibition of serum BuChE activity to those pretreated with corn oil following administration of 167 mg/kg malathion. Pretreatment with the EBI fungicide penconazole (200 mg/kg) produced significantly greater depression of serum BuChE activity at 1, 4, and 24 h after dosing with malathion, when compared to corn oil controls. The tendency toward increased inhibition of serum BuChE activity by each of the OPs in prochloraz-pretreated birds was attributed to an increased activation of the compound to its active oxon form as a consequence of induction of microsomal monooxygenases by prochloraz.

Interactive effects of prochloraz and malathion in pigeon, starling and hybrid red‐legged partridge

AbstractRecent laboratory studies with hybrid red‐legged partridges have shown that the interaction of certain combinations of agricultural pesticides can lead to an enhancement of toxicity. In view of this finding, captive feral pigeons (Columba livia) and European starlings (Sturnus vulgaris), in addition to hybrid red‐legged partridges (Alectoris rufa cross), were used in a laboratory study to extend investigations of the enhancement of toxicity of the organophosphorus (OP) insecticide malathion in birds predosed with the ergosterol‐biosynthesis‐inhibiting (EBI) fungicide, prochloraz. Following pretreatment with either 90 or 180 mg/kg prochloraz, both pigeons and partridges showed significantly greater inhibition of serum butyrylcholinesterase (BuChE) activity (1.4‐ to 2.1‐fold increase for pigeons and 1.3‐ to 3.8‐fold increase for partridges) when dosed with malathion than control birds; this difference was evident at some or all of the blood‐sampling time points. On the other hand, starlings given either 180 or 300 mg/kg prochloraz showed no difference from controls in serum BuChE inhibition after dosing with malathion. The enhanced inhibition of serum BuChE in the pigeon and the partridge after malathion dosing was attributed to the increased activation of malathion to malaoxon following induction of the hepatic monooxygenase system by prochloraz. Serum BuChE inhibition may be useful in studying the interactive effects of OPs and EBI fungicides in the field.

Synergism between EBI fungicides and a pyrethroid insecticide in the honeybee (Apis mellifera)

AbstractThe synergistic effect of a range of ergosterol‐biosynthesis‐inhibiting (EBI) fungicides and a pyrethroid insecticide was studied in the honeybee (Apis mellifera L.). Various EBI fungicides were combined separately with the pyrethroid lambda‐cyhalothrin at ratios derived from their recommended application rates to represent tank‐mixing in the field. The mixture was then applied topically to the thorax of honeybees, and mortality assessed 24 h post‐treatment. All the fungicides tested increased the toxicity of lambda‐cyhalothrin to honeybees. The fungicide propiconazole was found to have the strongest synergistic effect, decreasing the LD50 of lambda‐cyalothrin from 68.0 ng bee−1 to 4.2 ng, thus having a synergistic ratio of 16.2. Hazard ratios were calculated for lambda‐cyhalothrin and fungicide mixtures using a recommended application rate of 7.5 g a.i. ha−1. The hazard ratio for lambda‐cyhalothrin alone was 110, but when mixed with fungicide synergists, the hazard ratio ranged from 366 with flutriafol to 1786 with propiconazole. A blank formulation of a fungicide (without the active ingredient prochloraz) had little effect on the toxicity of lambda‐cyhalothrin, indicating that it is primarily the fungicide active ingredient that is responsible for the synergistic effect. The results are discussed in terms of the potential hazard posed by pesticide synergism to honeybees in the field.

Effects of Postinfection Applications of Ergosterol Biosynthesis-Inhibiting Fungicides on Lesion Formation and Pseudothecial Development of Venturia inaequalis

Effects of Postinfection Applications of Ergosterol Biosynthesis-Inhibiting Fungicides on Lesion Formation and Pseudothecial Development of Venturia inaequalis