Ortho-aminoacetophenone,a non-lethal repellent: The effect of volatile cues vs. direct contact on avoidance behavior by rodents and birds

Taxonomic differences in responsiveness to chemosensory irritants are prevalent among avian and mammalian species and represent a major obstacle to the development of general vertebrate repellents. We evaluated the effect of ortho-aminoacetophenone (OAP), a potent avian repellent, on ingestive behavior of two rodent species, Prairie vole (Microtus ochrogaster), Deer Mouse (Peromyscus maniculatus Wagn.), and an avian species, European starling (Sturnus vulgarus L.) utilizing similar experimental conditions to facilitate interspecies comparisons. All three species avoided OAP-treated food. Apple consumption by voles was decreased from a baseline of theoretical zero% by OAP (0·01–10·0 ml liter⁻¹), P <0·000 01, while mice avoided all but the lowest concentration of OAP (0·01−10 ml liter⁻¹), P <0·000 01. A repellent should elicit avoidance behavior prior to the animal having physical contact with the commodity, ideally producing aversion via volatile cues rather than through direct contact. Therefore, we utilized two delivery methods for presentation of the test solutions to evaluate the repellency of OAP in the presence and absence of direct contact. Apple consumption by birds following exposure to OAP by either direct contact or volatile cues differed from a baseline of theoretical zero% consumption, P < 0·001. When birds had access to OAP through both direct and volatile exposures, reduction in apple consumption by European starlings was greater than observed following contact with the compounds volatile cues alone, P < 0·03. These findings argue against a major role for olfaction or nasotrigeminal chemoreception in avoidance of OAP-treated food. Instead, taste or oral trigeminal chemoreception appear to mediate responding.     

Comparative SAR Evaluations of Annonaceous Acetogenins for Pesticidal Activity

The activities of 44 Annonaceous acetogenins, which were originally isolated by monitoring plant fractionations with the brine shrimp lethality test (BST), were evaluated in the yellow fever mosquito larvae microtiter plate (YFM) assay. The results clearly demonstrate that most acetogenins have pesticidal properties. The structure–activity relationships indicate that the compounds bearing adjacent bis-THF (tetrahydrofuran) rings with three hydroxyl groups are the most potent. Bullatacin ( 1 ) and trilobin ( 7 ) gave the best activities against YFM with LC₅₀ values of 0·10 and 0·67 mg litre^-1, respectively. Compounds showing LC₅₀ values below 1·0 mg litre^-1 in this assay are usually considered significant as new lead candidates for pesticidal development. In the BST, the corresponding LC₅₀ values were 1·6×10^-3 ( 1 ) and 9·7×10^-3 ( 7 ) mg litre^-1. This is the first report of pesticidal structure–activity relationships for a series of Annonaceous acetogenins which are known to act, at least in part, as potent inhibitors of mitochondrial NADH: ubiquinone oxidoreductase. © of SCI.     

Pharmacokinetics of fenvalerate after intravenous administration to sheep

The pharmacokinetics of total radioactivity and of intact fenvalerate were determined in sheep treated intravenously with radiolabelled or non-radiolabelled fenvalerate. Mean residence times (MRT) of total radioactivity and intact fenvalerate in plasma were 910 (±75) and 39 (±3) min, while harmonic mean elimination-phase half-lives (TM_β) were 990 and 82 min, each respectively. Systemic clearance values (Cl_S) of total radioactivity and intact fenvalerate were 2·8 (±0·3) ml min⁻¹ kg⁻¹ and 51·3 (±5·9) ml min⁻¹ kg⁻¹, respectively. Volumes of distribution at steady state (V_SS) were each near 2500 ml kg⁻¹. Elimination of radioactivity occurred, in part (33·3 (±3·3)% of dose), by renal excretion, at a rate (0·9 (±0·1) ml min⁻¹ kg⁻¹), similar to that of glomerular filtration. These data are consistent with a disposition model according to which intact fenvalerate was rapidly distributed into a peripheral compartment, where metabolism occurred. In addition, since the elimination half-life of fenvalerate from plasma was less than 90 min after intravenous injection, ‘flip-flop’ kinetics should be considered when longer elimination half-lives are observed after oral or dermal exposures.     

Relationship between the Spray Droplet Density of Two Protectant Fungicides and the Germination of Mycosphaerella fijiensis Ascospores on Banana Leaf Surfaces

The effect of fungicide spray droplet density (droplet cm^-2), droplet size, and proximity of the spray droplet deposit to fungal spores was investigated with Mycosphaerella fijiensis ascospores on the banana (Musa AAA) leaf surface for two contact fungicides: chlorothalonil and mancozeb. When droplet size was maintained at a volume median diameter (VMD) of 250 μm while total spray volume per hectare changed, M. fijiensis ascospore germination on the leaf surface fell below 1% for both fungicides at a droplet deposit density of 30 droplet cm^-2. At a droplet deposit density of 50 droplet cm^-2, no ascospores germinated in either fungicide treatment. When both droplet size and droplet cm^-2 varied while spray volume was fixed at 20 litre ha^-1, ascospore germination reached 0% at 10 droplet cm^-2 (VMD=602 μm) for both fungicides. At lower droplet densities (2–5 droplet cm^-2 VMD=989 μm and 804 μm respectively), ascospore germination on the mancozeb-treated leaves was significantly lower than on the chlorothalonil-treated leaves. The zone of inhibition surrounding a fungicide droplet deposit (VMD=250 μm) on the leaf surface was estimated to extend 1·02 mm beyond the visible edge of the spray droplet deposit for chlorothalonil and 1·29 mm for mancozeb. The efficacy of fungicide spray droplet deposit densities which are lower than currently recommended for low-volume, aerial applications of protectant fungicides was confirmed in an analysis of leaf samples recovered after commercial applications in a banana plantation. Calibrating agricultural spray aircraft to deliver fungicide spray droplets with a mean droplet deposit density of 30 droplet cm^-2 and a VMD between 300 and 400 μm will probably reduce spray drift, increase deposition efficiency on crop foliage, and enhance disease control compared to aircraft calibrated to spray finer droplets. © 1997 SCI.     

The role of pendimethalin in the integrated management of propanil-resistant Echinochloa colona in Central America

Pre-emergence activity of pendimethalin on propanil-resistant jungle rice (Echinochloa colona) was demonstrated in glasshouse trials. Both susceptible and resistant populations, collected from Costa Rica, were controlled by 1·25 kg ha^-1, the usual application rate used in the field where Rottboellia cochinchinensis is also a problem. When applied post-emergence, propanil performance was improved by the addition of low doses of pendimethalin to the herbicide mixture. A propanil-resistant selection was controlled by 0·23 kg ha^-1 pendi-methalin+0·54 kg ha^-1 propanil at the one-to-two leaf stage, and 0·23 kg ha^-1 pendimethalin+1·08 kg propanil at the three-to-four leaf stage compared to 1·08 kg and 2·16 kg ha^-1 respectively when propanil was applied alone. This suggests that pendimethalin improves post-emergence control in the field compared to the standard propanil treatment and can provide residual pre-emergence control of late-germinating individuals, so reducing the propanil selection pressure. For effective jungle rice control, growers apply propanil (3·84 kg ha^-1) at 10 and 20 days after planting (DAP) followed by one application of fenoxaprop-P-ethyl (0·045 kg ha^-1) at 35 DAP. Field experiments, conducted in dry-seeded upland rice in southern Costa Rica, demonstrated that under high jungle-rice population pressure, one application of pendimethalin at 1·5 kg ha^-1 provided an effective replacement for propanil, resulting in reduced weed-control costs. ©1997 SCI     

Pharmacokinetics of Intravenous Fenvalerate in Cattle Treated Topically with a Low Dose of Piperonyl Butoxide

Experiments were conducted to identify pharmacokinetic interactions between topically applied piperonyl butoxide and intravenous fenvalerate in cattle (Angus steers). Intact fenvalerate in plasma was derivatized by condensation with acetone and measured by negative chemical ionization gas chromatography/mass spectrometry. Noncompartmental pharmacokinetic analyses indicated that the elimination-phase rate constant (β, 0·00069 (±0·00006) min^-1), mean residence time (172 (±14) min), systemic clearance (10·4 (±0·7) ml min^-1 kg^-1) or volume at steady state (1800 (±230) ml kg^-1) were not changed (P>0·05) after topical application of a low dose of piperonyl butoxide. These data indicate that topical application of a low dose of the metabolic synergist piperonyl butoxide would not be expected to modify the in-vivo disposition of fenvalerate in cattle. © of SCI.     

Synthesis and Evaluation of New Ethyl 2,3- Dihydro-3-oxoisothiazolo[5,4-b]pyridine- 2-alkanoate Derivatives as Potential Herbicides

Several ethyl 2,3-dihydro-3-oxoisothiazolo[5,4-b]pyridine-2-alkanoate derivatives were synthesized as herbicides. Only 5-methyl derivatives inhibited both hypocotyl and root growth in the lettuce (Lactuca sativa L.) seedling test at 100 mg litre^-1. Only ethyl propionate and valerate derivatives showed significant inhibition at 0·1 mg litre^-1, whereas ethyl acetate or butyrate derivatives were inactive. Contrary to unoxidized derivatives, the inhibitory effect of 1-oxide and 1,1-dioxide derivatives was strongly dependent on concentration; ethyl 2,3-dihydro-5-methyl-3-oxoisothiazolo[5,4-b]pyridine-2-propionate 1,1-dioxide inhibited 100% of germination at 100 mg litre^-1 and 45% of lettuce seedling growth at 0·1 mg litre^-1. Quantitative structure–inhibition of growth relationship analysis carried out by adaptive least-squares (ALS) method gave a good correlation with small and hydrophobic 5-substituents as well as with odd carbon-chain ethyl alkanoates in position 2. Active compounds did not show auxin-like activity from 0·1 to 100 mg litre^-1. © 1997 SCI.     

Insecticidal activity against Aedes aegypti of m-pentadecadienyl-phenol isolated from Myracrodruon urundeuva seeds

BACKGROUND: Myracrodruon urundeuva Fr. Allemao is a common tree in the Caatinga that has been widely used for various medical purposes. Previous studies showed that the ethanol seed extract of M. urundeuva has potent activity against the larval stage of the dengue vector Aedes aegypti. Given this potential insecticidal activity, bioguided separation steps were performed in order to isolate the active compound(s). RESULTS: The isolation process resulted in only one active chemical compound, identified by infrared spectroscopy and mass spectrometry as m-pentadecadienyl-phenol. This compound presented potent larvicidal and pupicidal activity (LC₅₀ 10.16 and 99.06 µg mL⁻¹ respectively) and great egg hatching inhibitory activity (IC₅₀ 49.79 µg mL⁻¹). The mode of action was investigated through observations of behavioural and morphological changes performed in third-instar larvae treated with m-pentadecadienyl-phenol solution after 1, 6, 12, 16 and 20 h of exposure. Some changes were observed as flooding of the tracheal system, alterations in siphonal valves and anal gills and lethargy, probably caused by the strong anticholinesterasic activity reported previously. CONCLUSION: The compound isolated from M. urundeuva seeds, m-pentadecadienyl-phenol, showed potent activity against immature stages of dengue vector, Ae. aegypti, being considered the main larvicidal principle. Copyright © 2012 Society of Chemical Industry     

Deposition of aerially applied tebufenozide (RH5992) on balsam fir (Abies balsamea) and its control of spruce budworm (Choristoneura fumiferana [Clem.])

A field trial was conducted in 1994 to determine the foliar deposit of tebufenozide (RH5992), applied aerially, and its efficacy against spruce budworm, Choristoneura fumiferana (Clem.). A commercial 240 g litre^-1 formulation of the insecticide (Mimic 240LV) was mixed with water, dyed with a tracer dye (Rhodamine WT) and sprayed with a light fixed-wing aircraft. Six application strategies were tested. Five used 70 g AI ha^-1 in a spray volume of 1 or 2 litre^-1 ha^-1 with single or double applications; the sixth was an unsprayed control. Results show that the spectra of the spray applications were, with one exception, fairly uniform. Volume and number median diameters ranged from 100 to 130 μm and 27 to 72 μm, respectively. Mean number of drops cm^-2 on Kromekote cards were <2·0 for strategies where either 1 or 2 litre ha^-1 were sprayed. Nevertheless no one strategy produced droplet densities that were significantly different (P<0·05) from the other strategies. Tebufenozide recovered from foliage averaged 2·5 to 5·9 μg g foliage^-1 when 1 litre ha^-1 was sprayed and 5·8 to 6·8 μg g foliage^-1 after 2 litre ha^-1 were sprayed. When a single application was the strategy used, the mean number of droplets cm^-2 and μg tebufenozide g foliage^-1 ranged from 1·2 to 1·4 and 2·5 to 5·9, respectively. With double applications, the same response parameters ranged from 0·3 to 1·9 and 2·5 to 6·8, respectively. Budworm population reductions (%) and the number of larvae that survived tebufenozide treatments were significantly different (P<0·05) from the controls. After strategies that used 1 litre spray ha^-1, mean percentage population reductions ranged from 61·4 to 93·6 whereas populations were reduced by 85·6 to 98·3% when 2 litre ha^-1 were sprayed. After double applications the mean percentage population reductions ranged from 93·6 to 98·3, but single application strategies resulted in mean reductions of 61 to 86%. Mean population reductions in the controls were 61%. The mean number of larvae per branch that survived spray strategies of 1 litre ha^-1 ranged from 1·3 to 7·4, and from 0·4 to 1·3 when 2 litre ha^-1 was the spray volume. In the controls an average of 10·2 larvae survived. With one exception, mean percentage defoliation in the treated areas was also significantly less (P<0·05) than that in the control. Mean defoliation in trees sprayed at 1 litre spray ha^-1 ranged from 40 to 62·8% whereas those treated at 2 litre ha^-1 had mean defoliation levels from 31·5 to 62·8%. In contrast, average defoliation in the controls was 92·1%. When a single application was the spray strategy, mean defoliation ranged from 31·5 to 62·8%. These data imply that a double application of tebufenozide at 70 g in 2 litre ha^-1 was the most efficacious strategy. However, analyses of the data also show that the primary influence on deposits and defoliation was interactions between number of applications and spray. Nevertheless the two independent variables acted without significant interactions when influencing percentage reductions of spruce budworm populations. © 1998 SCI     

Effect of ABT on the activity and rate of degradation of isoproturon in susceptible and resistant biotypes of Phalaris minor and in wheat

The effect of the monooxygenase inhibitor, 1-aminobenzotriazole (ABT) on isoproturon phytotoxicity and metabolism was studied in resistant (R) and susceptible (S) biotypes of Phalaris minor and in wheat (Triticum aestivum). Addition of ABT (2·5, 5 and 10 mg litre^-1) to isoproturon (0·25, 0·5, 1, 2 and 4 mg litre^-1) in the nutrient solution significantly enhanced the phytotoxicity of isoproturon against the R biotype. Isoproturon at 0·25 mg litre^-1 reduced the dry weight (DW) of the S biotype by 77%, whereas the R biotype required 4·0 mg litre^-1 for similar reduction. Addition of 10 mg litre^-1 of ABT to the 0·25 mg litre^-1 isoproturon caused 71 and 82% reduction in DW of R and S biotypes, respectively. Wheat was more sensitive to the mixture of isoproturon and ABT than the R biotype of P. minor. Reduced concentrations of ABT in the mixture from 10 to 2·5 mg litre^-1 increased the DW of the R biotype more than that of the S biotype. The R biotype metabolised [¹⁴C]isoproturon at a faster rate than the S biotype. ABT (5 mg litre^-1) inhibited the degradation of [¹⁴C]isoproturon in both biotypes of P. minor and in wheat. In the presence of ABT, about half of the applied [¹⁴C]isoproturon remained as parent herbicide in all the three species after two days. The metabolites were similar in the R and S biotypes and wheat as determined by co-chromatography with reference standards and mass spectroscopy (MS). ABT inhibited the appearance of the hydroxy and monomethyl metabolites and their conjugates in all the test plants. These results suggest that the activity of the enzymes responsible for the degradation of isoproturon is greater in the R than in the S biotype of P. minor, resulting in its rapid detoxification. Incorporation of the monooxygenase inhibitor ABT into the nutrient solution greatly inhibited the degradation of [¹⁴C]isoproturon in the R biotype and increased its phytotoxicity. Both hydroxylation and N-dealkylation reactions were found to be sensitive to ABT; inhibition of hydroxylation was greater than that of demethylation. Since ABT could not completely suppress isoproturon degradation, it is possible that more than one monooxygenase is involved. © 1998 SCI     

Effect of the ecdysone agonists,RH-2485 and tebufenozide,on the southwestern corn borer,Diatraea grandiosella

The effect of the ecdysone agonists RH-2485 (proposed name methoxyfenozide) and tebufenozide (RH-5992), was examined on eggs and larvae of the southwestern corn borer, Diatraea grandiosella Dyar. Both compounds exhibited a concentration-dependent ovicidal activity. More than 95% of eggs died when egg masses were dipped in solutions of 100 or 200 mg liter^-1 of either compound in acetone+distilled water (1+1 by volume). Although some eggs treated with 1 or 10 mg liter^-1 of the compounds hatched, the survival rate was low. Newly hatched larvae were fed for seven days on an artificial diet containing RH-2485 or tebufenozide. The LC₅₀ values were 0·049 mg kg^-1 for RH-2485 and 0·185 mg kg^-1 for tebufenozide, showing that RH-2485 was about four times more active than was tebufenozide. Although increasing the time of exposure to either compound decreased the LC₅₀ value significantly, the relative potency of RH-2485 versus tebufenozide was not changed. Newly ecdysed 4th-instar larvae fed with diets containing 0·125, 0·25 or 0·5 mg kg^-1 RH-2485 or tebufenozide ceased feeding approximately 8 h after exposure, indicating that larvae had prematurely entered a molting cycle. Larvae treated with RH-2485 ecdysed earlier and died more quickly than those treated with tebufenozide. Ingestion of sublethal concentrations of RH-2485 (0·005 and 0·01 mg kg^-1) or tebufenozide (0·03 and 0·06 mg kg^-1) retarded larval growth, and decreased pupal weight and adult emergence. Increasing exposure time to tebufenozide tended to increase the larval mortality, significantly retarded larval growth, and decreased the mean weights of male and female pupae and adult emergence. RH-2485 (0·125 and 0·25 mg kg^-1) and tebufenozide (0·25 and 0·5 mg kg^-1) were lethal to newly hatched larvae, even after diets containing these compounds were held for 20 days at 30°C under long days (16 h light: 8 h dark). Our results suggest that field trials to assess the potential of RH-2485 and tebufenozide to control D. grandiosella are warranted. © 1998 SCI     

Synthesis and Structure–Activity Relationships for the Fungicidal Activity of O,O-bisaryl sec-butylphosphonates

Sixteen O,O-bisaryl sec-butylphosphonates have been synthesised by condensing sec-butylphosphonyl dichloride with substituted phenols. The compounds were tested against two phytopathogenic fungi, Rhizoctonia bataticola and Helminthosporium oryzae. The most active compound against R. bataticola is O,O-bis(3-methylphenyl) sec-butylphosphonate (ED₅₀ 29·56 mg litre^-1) and against H. oryzae, O,O-bis(2-chlorophenyl) sec-butylphosphonate and its para-chloro analogue (ED₅₀ 0·14 and 0·13 mg litre^-1 respectively). Quantitative structure–activity relationships on the fungicidal activity have been analysed by means of multiple regression analysis using physicochemical substituent parameters. Electronic parameters viz., σ and F have expressed significant variability in fungitoxicity against both the fungi, viz. R. bataticola and H. oryzae. Hydrophobic and steric parameters are also found to be important in the correlation studies. © 1997 SCI.     

Ovicidal,larvicidal and juvenilizing activity of a picolinephenoxyanilide against Cydia pomonella

N‐(4‐phenoxyphenyl)‐2‐pyridinecarboxamide (1) was synthesized from commercially available materials and its ovicidal and larvicidal activity against Cydia pomonella (L) was tested. The compound showed a LC₅₀ of 0.98 mg ml⁻¹ when eggs less than 24 h were sprayed using a Potter Tower, but it had no effect when eggs older than this were sprayed. The compound did not have larvicidal activity when larvae were treated with 1200 µg g⁻¹. However, the larval head capsules were smaller than those in the controls when treated at this concentration. To assess its possible juvenile‐hormone‐like activity, the compound was topically applied to young pupae of Tribolium confusum duVal, where it produced clear juvenilization effects, which were dependent on the applied dose. © 2000 Society of Chemical Industry     

Leaching of Methyl Isothiocyanate in Plainfield Sand Chemigated with Metam-Sodium

Soil column studies were undertaken to investigate the influence of soil water content and irrigation on leaching, distribution and persistence of methyl isothiocyanate (MITC) in a sandy soil chemigated with the soil fumigant metam-sodium. No leaching was obtained from columns at low water content (0·042 or 0·074 cm³ cm⁻³). However, 8·4 (±2·8), 34·2 (±7·4) and 119·4 (±8·3) μg of MITC leached from columns at 0·105, 0·137 and 0·168 cm³ cm⁻³ water content, respectively. Increased leaching resulted from sprinkler application of 25-mm of water to columns at 0·137 cm³ cm⁻³ water content. Leaching of MITC constituted only a small fraction of the amount applied even in the worst case. Methyl isothiocyanate persisted in soil for 15 days at 2°C in varying amounts under the different water regimes. Relatively high amounts of MITC residues (8–12 mg kg⁻¹ soil) were detected in the top 25-cm layer of all the soil columns. Degradation was the major pathway of dissipation for the chemical despite the soil water regime.     

Bacterial pathogens of rice in the Kingdom of Cambodia and description of a new pathogen causing a serious sheath rot disease

A study of rice diseases in Cambodia from 2005 to 2007 showed widespread occurrence of diseases caused by Acidovorax avenae subsp. avenae, Burkholderia gladioli, B. cepacia and Pantoea ananatis. This is the first report of these pathogens in Cambodia. Additionally, a pseudomonad causing a widespread disease similar to sheath brown rot (caused by Pseudomonas fuscovaginae) was isolated. The studied strains were pathogenic to rice cvs Sen Pidau and IR 66, producing similar, though slightly less severe, symptoms to those observed in the field. Based on comparative 16S rDNA gene sequence analysis, combined with cell wall fatty acid analysis and metabolic profiles, the isolated strains were allocated to the genus Pseudomonas. The novel species were differentiated from Pseudomonas fuscovaginae and P. putida by their inability to metabolize d ‐fructose, d ‐galactose, d ‐galactonic acid lactone, d ‐galacturonic acid, d ‐glucosaminic acid, d ‐glucuronic acid, p‐hydroxy phenylacetic acid, d ‐saccharic acid and urocanic acid. The major fatty acids were C_16:0, summed feature 3 (C_16:1ω7c and C_16:1ω6c) and summed feature 8 (C_18:1ω7c), representing 80% of the total. Partial 16S rRNA gene sequences (1460 bp) were identical, except for two nucleotide changes amongst the six strains. Alignment of the causal strains within type‐culture databases revealed similarities of 99·7% with Pseudomonas parafulva AJ 2129^T, 99·2% with P. fulva IAM 1592^T, 98·9% with P. plecoglossicidia FPC 951^T, and 98·1% with P. fuscovaginae MAFF 301177^T. On the basis of data from this polyphasic study, it is proposed that the unknown strains isolated from rice represent a novel species of the genus Pseudomonas.     

Structural modifications increase the insecticidal activity of ryanodine

The toxicity of ryanodine ( 1 ) and 9,21-didehydroryanodine ( 2 ) (the principal active ingredients of the botanical insecticide ryania) to adult female house flies (Musca domestica L.) is attributable to binding to the ryanodine receptor (ryr) and thereby disrupting the Ca²⁺-release channel. These ryanoids, assayed in house flies with piperonyl butoxide (PBO) to suppress cytochrome P450-dependent detoxification, give injected KD₅₀ values of 0·07–0·11 μg g^-1, injected LD₅₀ values of 0·39–0·45 μg g^-1 and topical LD₅₀ values of 12– 50 μg g^-1. They inhibit the [³H]ryanodine binding site of house fly and rabbit muscle with IC₅₀ values of 3–10 nM . This study examines the effect of structure on potency, with 15 variants of the cyclohexane substituents, two 4,6-cyclic boron and two methylated derivatives, and four modifications of the isopropyl and ester substituents. The most effective compound examined was 10-deoxy- 2 ( 3 ) which was more potent than 2 by 2–4-fold on injection and 29-fold applied topically following PBO (LD₅₀ 0·41 μg g^-1). Additional high-potency compounds were 10-oxo- 1 and the cyclohexane variants with lactam, 21-nor-9-oxo and 21-nor-10-deoxy substituents. Other modifications usually reduced toxicity. The injected knockdown potency of the ester ryanoids was generally related to their effectiveness in competing with [³H]ryanodine at the ryr of rabbit skeletal muscle. Two non-ester ryanoids, ryanodol and 9,21-didehydroryanodol, were found to be more toxic than predicted from their potency at the ryr and may therefore act in a different manner such as at a K⁺ channel, as suggested by Usherwood and Vais. Clearly ryanoids are challenging prototypes for a potential new generation of insecticides. © 1997 SCI.     

Multiple Resistance in the Larger House Fly Musca domestica in Germany

Populations of the housefly Musca domestica isolated from farms in different German districts with strong resistance problems were compared to laboratory strains with varying resistance spectra. Resistance against pyrethroids, organophosphates and carbamates was tested using impregnated filter papers, and by topical application using a susceptible housefly strain (origin WHO) for comparison. The multi-resistant fly strains tested had a strong resistance against these insecticide groups, ranging from 37- to >10000-fold for organophosphates and 150- to >6600-fold for pyrethroids. The constituent enantiomer pairs of the α-cyano-pyrethroid cyfluthrin were tested, as was beta-cyfluthrin. With respect to multi-resistant fly strains, the isomers II and IV had the best activity, with LD₅₀ values of 0·012 and 0·014 μg per fly, respectively. In addition, different groups of insect growth regulators (juvenile hormone analogues, chitin synthesis inhibitors and one triazine derivative) were tested in a special larvicidal test. The chitin synthesis inhibitors were quite effective against multi-resistant M. domestica strains except for one strain with strong resistance against chitin synthesis inhibitors, developed after extensive treatments with benzoylphenylureas for several years. The fly strains tested were not resistant against cyromazine. Additionally, the insecticides were combined with the synergists piperonyl butoxide, tributylphosphorotrithioate (DEF) and Cibacron blue and tested against the fly strain with the strongest resistance spectrum (‘Grimm’) in comparison to the susceptible strain (‘WHO-N’). Piperonyl butoxide had the greatest effect on the efficacy of cyfluthrin followed by Cibacron blue and DEF. In a parallel investigation with susceptible and resistant house fly strains, different enzyme activities related with resistance mechanisms were tested, e.g. glutathione S-transferase (3·5-fold) and mixed-function oxidase (2·3-fold). Implications of these results for management of insecticide resistance in M. domestica are discussed.     

Polydisperse ethoxylated fatty alcohol surfactants as accelerators of cuticular penetration. 1. Effects of ethoxy chain length and the size of the penetrants

The effects of polydisperse ethoxylated fatty alcohol (EFA) surfactants on the penetration of six organic compounds varying in size (molar volumes, 107–282 cm³ mol^-1) and lipophilicity (log K_ow 0·8–6·5) were investigated using astomatous isolated cuticular membranes (CM) of Citrus and pear leaves. Mobilities of model compounds in CM were measured by unilateral desorption from the outer surface (UDOS). Rate constants (k*) obtained in these experiments are directly proportional to diffusion coefficients and, in the absence of EFA, k* values decreased by a factor of 52 when molar volumes increased only 2·64-fold. Under UDOS conditions using micellar surfactant solutions as desorption media, surfactants are sorbed in the CM and the volume fractions sorbed were found to decrease from approximately 0·062 to 0·018 when the average number of ethoxy groups (nE) increased from 5 to 17. In the presence of the EFA surfactants in the CM, solute mobilities increased markedly though this effect diminished with increasing nE. Surfactants with nE=17 affected solute mobilities only marginally. Surfactant effects on solute mobility increased with the size of the solutes leading to almost identical mobilities of the model compounds. With the current range of our model compounds, lipophilicity increased with increasing molar volumes, though evidence is presented showing that the mobilities of solutes depend on their molar volumes while lipophilicity has no effect. Effects of micellar aqueous solutions of polydisperse surfactants on solute mobilities followed the pattern observed with monodisperse ones. © 1997 SCI     

Presence of Muscarinic Acetylcholine Receptors in the Cattle Tick Boophilus microplus and in Epithelial Tissue Culture Cells of Chironomus tentans

A muscarinic acetylcholine receptor (mAChR) has been demonstrated and partially characterized in larvae of the cattle tick Boophilus microplus. Its properties are compared with mAChR from an epithelial cell line from the dipteran insect Chironomus tentans. Competition studies with cholinergic ligands of different specificity revealed the muscarinic nature of the cholinergic receptors investigated in both species. In homogenates from tick larvae, specific binding sites for [³H]quinuclidinyl benzilate (QNB) with high affinity (1·2±(0·13) nM ; B_max 22·5 pmol mg protein⁻¹) were detected that do not bind nicotinic compounds specifically. The estimated IC₅₀ values for nicotine, imidacloprid and α-bungarotoxin were all in the mM range. Additionally, with tick larvae, high-affinity nicotinic binding sites were detected with [³H]nicotine which could be displaced by high concentrations of imidacloprid or QNB. The estimated IC₅₀ values for nicotine, α-bungarotoxin, imidacloprid and QNB were 43(±8) nM , 0·8(±0·2) μM , 2·8(±0·6) μM and 78(±1·9) μM , respectively. With homogenates of the non-neuronal insect cell line from C. tentans, only high-affinity binding sites for [³H]QNB were found. Muscarinic antagonists selectively displaced [³H]quinuclidinyl benzilate (QNB) binding to tick larvae homogenates. The mAChR of B. microplus preferred pirenzepine (IC₅₀ 2·13(±1·02) μM ) among different subtype-specific mAChR antagonists (4-DAMP had IC₅₀ 49·9(±9·13) μM and methoctramine had IC₅₀ 121(±14·2) μM ) indicating a type of binding site similar to the vertebrate M1 mAChR subtype. The tick muscarinic receptor seems to be a G-protein-coupled receptor, as concluded from the 4·8-fold reduction in receptor affinity for binding of the muscarinic agonist oxotremorine M upon treatment with the non-hydrolysable GTP-analogue γ-S-GTP. Binding data for the agonists oxotremorine M (IC₅₀ 71·3(±19·6) μM ) and carbachol (IC₅₀ 253(±87·1) μM ) parallel the biological efficacy of these compounds, in that, while oxotremorine M showed some activity against ticks, carbachol was ineffective.     

Effect of chlorsulfuron on four graminicides for weed control and wheat yield

In field experiments with spring wheat (Triticum aestivum L., cv. Neepawa), the low rate (0·02 kg ha^-1) of chlorsulfuron significantly reduced wild oat control from individual applications of only barban and diclofop-methyl. The high rate (008 kg ha^-1) affected wild oat control by all four graminicides, including difenzoquat and flam-prop-methyl. In most cases, the graminicides did not affect the broad-leaved weed control of chlorsulfuran. Overall, a low rate of chlorsulfuron in mixture with graminicides did not reduce wheat yield, whereas a high rate of chlorsulfuron in the mixtures gave a significant yield reduction compared with individual graminicides applied alone. All herbicide treatments increased wheat yield over the control. In the glasshouse, reduction in wild oat control by diclofop-methyl was directly related to the rate of chlorsulfuron added to diclofop-methyl. The effect of 0·02 kg ha^-1 chlorsulfuron on control of wild oat was decreased when the rate of diclofop-methyl increased from 0·5 to 0·9 kg ha^-1 and was completely eliminated when diclofop-methyl reached 1·1 kg ha^-1. Conversely, diclofop-methyl (0·7 and 1·1 kg ha^-1) gave some reduction of wild mustard (Sinapis arvensis L.) and redroot pigweed (Amaranthus retrofiexus L.) control by chlorsulfuron (0·01 and 0·02 kg ha^-1), even though in some cases diclofop-methyl/chlorsul-furon gave better control of these broad-leaved weeds. In the laboratory, the absorption and translocation of [¹⁴C]-diclofop-nieihyl in wild oat seedlings were significantly reduced when chlorsulfuron was added, compared with [¹⁴C]-diclo-fop-methyl applied alone. Effet du chlorsulfuron sur l'efficacité et l'effet sur le rendement de quatre graminicides Dans des essais de plein champ sur blé de printemps (Triticuni aestivum L., cv. Neepawa), la faible dose (0, 02 kg ha^-1) de chlorsulfuron a réduit significativement l'efficacité d'une application séparée de barbane et de diclofop-methyl. La forte dose (0, 08 kg ha^-1) a contrarié la destruction de la folle avoine pour les quatre graminicides dont le difenzoquat et le flamprop-methyl. Dans la plupart des cas, les graminicides n'ont pas eu d'incidence sur la destruction des dicotylédones par le chlorsulfuron. Par ailleurs. une faible dose de chlorsulfuron en mélange avec les graminicides n'a pas réduit le rendement en blé, en revanche, une forte dose de chlorsulfuron en mélange a entrainé une baisse significative de rendement en comparaison des graminicides appliqués seuls. Tous les traitements herbicides ont entrainé un gain de rendement par rapport au témoin non traité. En serre, la réduction d'efficacité sur folle avoine du diclofop-methyl était directement correlée à la dose de chlorsulfuron ajouté. Les effets de 0, 02 kg ha^-1 sur la destruction de la folle avoine baissaient quand le niveau de diclofop-methyl augmentait de 0,5 à 0,9 kg ha^-1 et étaient complètement éliminés quand la dose de diclofop-methyl atteignait 1, 1 kg ha^-1. Par ailleurs, le diclofop-méthyl (0,7 et 1,1 kg ha^-1) a réduit l'efficacité du chlorsulfuron (0,01 et 0,02 kg ha^-1) sur la sanve (Sinapis arvensis L.) et l'amaranthe réflechie (Amaranthus retroflexus L.) même si dans certains cas l'association diclofop-mélhyl-chtorsulfuron a eu une meilleure efficacité sur ces mauvaises herbes. Au laboratoire, l'ab sorption et la translocation du diclofop-methyl C¹⁴ dans les plantules de folle avoine ont été réduites significativement par l'addition de chlor-sulfuron en comparaison du diciofop-méthyl C¹⁴ appliqué seul. Wirkung von Chlorsulfuron zusammen mil Vier Graminiziden auf die Unkrautbekämpfung und den Ertrag von Weizen In Freilandversuehen mit Sommerweizen (Triticum aesttotm L. ‘Neepawa’) verminderie Chlorsulfuron in niedriger Aufwandmenge (0,02 kg ha^-1) den Bekämpfungserfolg gegen Flug-Hafer nur bei Barban und Diclofop-menthyl. Die hohe Aufwandmenge (0,08 kg ha^-1)beeinträchtigte die Wirkung aller 4 Graminizide, einschliesslich Difenzoquat und Flamprop-methyl. Die Graminizide beeinfiussten die Wirkung von Chlorsulfuron gegen zweikeimblättrige Arten meistens nicht, Der Weizenertrag blieb bei der Mischung der niedrigen Aufwandmenge von Chlorsulfuron mit den Graminiziden unverändert, die hohe Aufwandmenge führte aber in den Mischungen zu einem signifikaten Abfall des Ertrags, vergli-chen mit dem bei Anwendung der Graminizide allein. Mit allen Herbizidbehandlungen wurden gegenüber Unbehandelt höhere Erträge erzielt. Im Gewächshaus war die Wirkung von Diclofopmethyl gegen Flug-Hafer direkt von der zugefügten Menge an Chlorsulfuron abhängig. Der Einfluss von 0,02 kg ha^-1 Chlorsulfuron aif die Bekämpfung von Fiug-Hafer nahm ab. wenn die Aufwundmenge von Diclofop-methyl von 0,5 auf 0,9 kg ha^-1 gesteigert wurde; bei 1, 1 kg ha^-1 Diclofop-methyl war er aufgehoben. Andererseits trat bei 0,7 und 1,1 kg ha^-1 Diclofop-methyl eine Minderung der Wirkung von Chlosulfuron (0,01 und 0,02 kg ha^-1) gegen Acker-Senf (Sina-psis arvensis L.) und Zurückgekrümmten Fuchsschwanz (Amarenthus retroflexus L.) ein, wenn auch dise Mischung in einigen Fällen gegen dise Arten starker wirkte. Im Labor wurde einc signifikant geringere Absorption und Trans-lokation von ¹⁴C-Diclofop-methyl in Keimpflan-zen des Flug-Hafers beobachtet, wenn Chlorsulfuron zugefügt worden war.