Effects of anti-ecdysteroid azole analogues of metyrapone on the larval development of the fleshfly,Neobellieria bullata

Based on our previous finding that PIM (phenyl-imidazolyl-metyra-pon; 2-(1-imidazolyl)-2-methyl-1-phenylpropan-1-one, 1) is a strong inhibitor of ecdysone 20-monooxygenase (IC₅₀ = 7.89 × 10^?7 M) from the fleshfly, Neobellieria bullata (Parker) and has also a good toxic action in vivo against this insect, 17 imidazole and 1,2,4-triazole analogues of metyrapone were synthesized and evaluated for their action against N. bullata larvae in terms of toxicity, length of larval development, weight of the puparium as well as special symptoms, i.e. malformations of the anterior and posterior spiracles, and of the mandibles. The introduction of p-methoxy (LC₅₀ = 49 mg kg^?1 in diet) or p-chloro (LC₅₀ = 97 mg kg^?1) substituents on the benzene ring of PIM resulted in a significant increase in toxicity compared to that of metyrapone (LC₅₀ = 561 mg kg^?1) and PIM (LC₅₀ = 148 mg kg^?1). The hybridization state of the carbon atom adjacent to the benzene ring was not an important factor for toxicity because the acetoxy derivative ( 13 ) was almost as toxic as PIM. At least one methyl group was required on the carbon atom adjacent to the azole ring to maintain activity, while an ethyl group ( 4 ) enhanced the toxic effect. At the applied doses some compounds including metyrapone itself, extended the duration of the larval development. Only metyrapone and PIM decreased the puparium weight. Several derivatives induced lethal malformations of mandibles as well as the anterior and posterior spiracles.     

Determination of baseline susceptibility of European populations of Tuta absoluta (Meyrick) to indoxacarb and chlorantraniliprole using a novel dip bioassay method

BACKGROUND: Tuta absoluta(Meyrick) is one of the most serious pests of tomato recently introduced in the Mediterranean region. A novel bioassay method designed for the accurate determination of insecticide toxicity on T. absoluta (IRAC method No. 022) was validated by three different laboratories [Greece (NAGREF), Italy (UC) and Spain (UPCT)] on European populations. RESULTS: The insecticides indoxacarb and chlorantraniliprole were used as reference products. The IRAC leaf dip method is easy to perform, producing repeatable, homogeneous responses. LC₅₀ values for indoxacarb ranged between 1.8 and 17.9 mg L^?1 (NAGREF), 0.93 and 10.8 mg L^?1 (UC) and 0.20 and 0.70 mg L^?1 (UPCT), resulting in a tenfold, 12‐fold and fourfold difference between the least and most susceptible populations at each laboratory respectively. For chlorantraniliprole, LC₅₀ values ranged between 0.10 and 0.56 mg L^?1 (NAGREF), 0.23 and 1.34 mg L^?1 (UC) and 0.04 and 0.24 mg L^?1 (UPCT), resulting in a sixfold difference in all three cases. Overall, UPCT reported lower mean LC₅₀ to indoxacarb, while UC reported higher LC₅₀ to chlorantraniliprole. CONCLUSIONS: The new bioassay is reliable, providing a useful tool in the design of IRM strategies. Within each country/lab, the variability observed in the results for both indoxacarb and chlorantraniliprole can be attributed to natural variation. Future research is necessary to determine the extent to which it is possible to compare results among laboratories. Copyright © 2012 Society of Chemical Industry     

Monitoring for imidacloprid resistance in the tobacco‐adapted form of the green peach aphid,Myzus persicae (Sulzer) (Hemiptera: Aphididae), in the eastern United States

BACKGROUND: Imidacloprid is the primary insecticide for controlling the tobacco‐adapted form of the green peach aphid (TGPA), Myzus persicae (Sulzer), a major pest of tobacco worldwide. This study used leaf‐dip bioassays to assess TGPA resistance to imidacloprid in the eastern United States from 2004 through 2007. RESULTS: When combined over the 4 year study, 18, 14 and 3% of the TGPA had imidacloprid resistance ratios (RRs) of 10–20‐fold, 20–30‐fold and 30–90‐fold, respectively, compared with the most susceptible colony tested. This indicates that some colonies have developed moderate levels of resistance to imidacloprid. A colony collected near Clayton, North Carolina, had the highest RR of 91 (LC₅₀ value = 31 mg L^?1). This resistance declined for six tests over a 3 year period in the laboratory culture from >130‐fold RR (LC₅₀ = 48 mg L^?1) to 40‐fold RR (LC₅₀ = 15 mg L^?1). Over the same period, the most susceptible colony and a standard colony not exposed to imidacloprid for over 7 years had consistently low LC₅₀ values. CONCLUSION: Moderate levels of resistance to imidacloprid are noticed among TGPA colonies from the eastern United States. The variation in resistance indicates that the factors responsible are present in the populations at low frequencies and are just not enough to cause field failures yet. Copyright © 2010 Society of Chemical Industry     

Disposition kinetics,cytotoxicity and residues of fenvalerate in tissues following oral administration to goats

Disposition kinetics in goats of fenvalerate [(RS)-α-cyano-3-phenoxybenzyl (RS)-2-(4-chlorophenyl)-3-methylbutyrate] were studied after oral administration at 5 mg kg^?1. The insecticide persisted in blood for up to 48 h. The V_d(area), t_1/2(β), and t_1/2(Ka), of fenvalerate were 12.14 (±0.39) litre kg^?1, 12.25 (±0.25) h and 0.63 (±0.11)h, while the AUC and Cl_B values were respectively 7.35 (±0.39) μg h ml^?1 and 0.68 (±0.04) litre kg^?1 h^?1. The residues in tissues reached a peak four days after insecticide administration and then started to decline. Maximum residue was found in the adrenal gland, followed by liver, kidney and intestine. Both GOT and GPT activities in kidney tissue, but only GPT activities in liver tissue had decreased significantly 4, 8 and 22 days post-administration. The fenvalerate did not produce any significant effects on serum acetylcholinesterase, cholesterol or protein levels in goats. Histopathological examination showed fatty changes in the periphery of lobule, congestion in sinusoid, haemolysis in central vein, necrosis and periportal fibrosis around the central vein of liver, and necrosis in kidney of fenvalerate-treated goats.     

Acute toxicity of the bird repellent,methyl anthranilate,to fry of Salmo salar,Oncorhynus mykiss,Ictalurus punctatus and Lepomis macrochirus

Several laboratory and field studies have shown methyl anthranilate to be an effective, non-toxic and non-lethal bird repellent, with application potential for protecting crops, seeds, turf and fish stocks from bird damage. Furthermore, methyl anthranilate can be added to liquids for the purposes of protecting migratory birds, e.g. addition to waste water associated with mining and to standing water pools at airports. Mammalian toxicity data are favorable. Methyl anthranilate is used as a fragrance and food flavoring and is GRAS listed by the US Food and Drug Administration. Despite the favorable outlook for methyl anthranilate's use as a safe repellent, no data exist on its environmental fate and effects. We have tested the acute toxicity of methyl anthranilate in a static system against the fry of four species of fish. The LC₅₀ at 24 h for Atlantic salmon (Salmo salar L.) was 32.3 mg liter^?1, with the no observable effect limit at 6 mg liter^?1. The LC₅₀ at 24 h for rainbow trout (Oncorhynus mykiss Richardson) was 23.5 mg liter^?1, with the no observable effect limit at 5 mg liter^?1. The LC₅₀ at 24 h for channel catfish (Ictalurus punctatus Raf.) was estimated to be 20.1 mg liter^?1, with the no observable effect limit at 7 mg liter^?1. The LC₅₀ at 24 h for bluegill sunfish (Lepomis macrochirus Raf.) was estimated to be 19.8 mg liter^?1, with the no observable effect limit at 7 mg liter^?1..     

The role of GABA and glutamate receptors in susceptibility and resistance to chloride channel blocker insecticides

Despite a point mutation in the pore-forming segment of the Rdl GABA receptor subunit that is widespread and persistent in insect populations and confers high levels of resistance to dieldrin and other polychlorocycloalkane (PCCA) insecticides, the phenylpyrazole insecticide fipronil, which binds at same site, has proven to be effective in controlling many insects, including dieldrin-resistant populations. Fipronil and its major sulfone metabolite are unique among chloride channel blocking insecticides in that they also potently block GluCls. We present here a patch clamp study of the action of fipronil sulfone on native GABA receptors and GluCl receptors from susceptible and dieldrin-resistant German cockroaches, to provide a better understanding of the effect of the Rdl mutation on the function and insecticide sensitivity of these two targets, and its role in resistance. Dieldrin blocked GABA currents with an IC₅₀ of 3 nM in wild-type cockroaches, and 383 nM in resistant insects, yielding a resistance ratio of 128. Fipronil sulfone blocked GABA currents with an IC₅₀ of 0.8 nM in susceptible insects and 12.1 nM, or 15-fold higher, in resistant insects. While both GluClD (desensitizing) and GluClN (non-desensitizing) receptors were found in German cockroach neurons, GluClN receptors were rare and could not be included in this study. GluClD receptors from resistant insects had reduced sensitivity to glutamate and a lower rate of desensitization than those from susceptible insects, but their sensitivity to block by fipronil sulfone was not significantly changed, with an IC₅₀ of 38.5 ± 2.4 nM (n = 8) in the susceptible strain and 40.3 ± 1.0 nM (n = 7) in the resistant strain. Fipronil sulfone also slowed the decay time course of GluClD currents. These results suggest that GluClD receptors contain the Rdl subunit, but their sensitivity to fipronil sulfone is not altered in resistant insects.     

Use of natural pyrethrum to control the red swamp crayfish Procambarus clarkii in a rural district of Italy

BACKGROUND: The crayfish Procambarus clarkii inflicts severe ecological and economic damages in Europe. To develop an efficient method for its control, four experiments were carried out to assess the impact of natural pyrethrum (i.e. Pyblast) on crayfish: (1) the 24 h LC₁₀₀ and LC₅₀ were quantified on crayfish; (2) the breakdown time of the 24 h LC₁₀₀ was assessed using Daphnia magna as a bioindicator; the effects of 24 h LC₁₀₀ on crayfish were investigated by applying the biocide into burrows (3) and in a drainage channel (4). RESULTS: Pyblast concentrations of 0.05 and 0.02 mg L^?1 corresponded to 24 h LC₁₀₀ and LC₅₀ respectively. The concentration of 0.05 mg L^?1 broke down after 72 h, whereas 0.02 mg L^?1 did not cause any significant mortality in D. magna after 24 h. However, 0.05 mg L^?1 had no effect on crayfish when introduced into the burrows, but led to a mortality of 95% when applied in the water. CONCLUSION: Experimental evidence is provided for the efficacy of Pyblast to control invasive crayfish. Obviously, before its use on a large scale, further studies are needed to find a concentration that will achieve the target 100% mortality with the shortest recovery time of the environment. Copyright © 2012 Society of Chemical Industry     

Evaluation of semiochemical toxicity to houseflies and stable flies (Diptera: Muscidae)

BACKGROUND: The housefly, Musca domestica L., and stable fly, Stomoxys calcitrans (L.) are cosmopolitan pests of both farm and home environments. Houseflies have been shown to be resistant to a variety of insecticides, and new chemistries are slow to emerge on the market. Toxicities of selected semiochemicals with molecular structures indicative of insecticidal activity were determined against adults from an insecticide‐susceptible laboratory strain of houseflies. The three most active semiochemicals were also evaluated against recently colonized housefly and stable fly strains. RESULTS: Nineteen semiochemicals classified as aliphatic alcohols, terpenoids, ketones and carboxylic esters showed toxicity to houseflies and stable flies. Rosalva (LC₅₀ = 25.98 µg cm^?2) followed by geranyl acetone and citronellol (LC₅₀ = 49.97 and 50.02 µg cm^?2) were identified as the most toxic compounds to houseflies. Permethrin was up to 144‐fold more toxic than rosalva on the susceptible strain. However, it was only 35‐fold more toxic to the insecticide‐tolerant field strain. The compounds generated high toxicity to stable flies, with LC₅₀ values ranging from 16.30 to 40.41 µg cm^?2. CONCLUSION: Quantification of LC₅₀ values of rosalva, citronellol and geranyl acetone against susceptible housefly and field‐collected housefly and stable fly strains showed that semiochemicals could serve as potent insecticides for fly control programs. Copyright © 2010 Society of Chemical Industry     

Residual toxicity and sublethal effects of chlorantraniliprole on Plutella xylostella (lepidoptera: plutellidae)

BACKGROUND: The diamondback moth (DBM), Plutella xylostella (L.), is the most important pest of cruciferous vegetables in the world. Chlorantraniliprole is a novel anthranilic diamide insecticide registered for the control of lepidopteran pests. The dose response, residual toxicity and sublethal effects of chlorantraniliprole applied for 48 h at LC₁₀ (0.02 mg L^?1) and LC₂₅ (0.06 mg L^?1) on P. xylostella were investigated. RESULTS: Leaf‐dip bioassays showed that chlorantraniliprole had a high level of toxicity against larvae of P. xylostella, and the 48 h LC₅₀ values were 0.23 and 0.25 mg L^?1 for a susceptible and field strain respectively. Chlorantraniliprole also had a long‐lasting effect when the larvae were exposed to chlorantraniliprole field sprayed on radish seedlings. Sublethal effects of chlorantraniliprole were indicated by reduced pupation, pupal weight and adult emergence rates. There was also an increase in the duration of female preoviposition period, decreased fecundity and egg hatch and decreased survival rates of the offspring. The mean values of the net reproductive rate (R₀), intrinsic rate of increase (r_m), finite rate of increase (λ) were significantly lower in the treatment than in control groups. CONCLUSIONS: These results indicate that chlorantraniliprole is effective against P. xylostella. The sublethal concentrations of chlorantraniliprole may reduce the population growth of P. xylostella by decreasing its survival and reproduction, and by delaying its development. Copyright © 2012 Society of Chemical Industry     

Lethal and sublethal effects of the neem insecticide formulation, ‘Margosan-O’, on the pea aphid

The effects of ‘Margosan-O’ (MO) on the pea aphid, Acyrthosiphon pisum (Harris), were determined. MO significantly reduced population increase of A. pisum in a concentration-dependent manner. At a concentration equivalent to 100 mg litre^?1 of azadirachtin, population increase was c. 3.5 times lower than the control. In more detailed studies, MO significantly reduced the number of molts, longevity, and fecundity of A. pisum that had been reared on treated broad bean. Viciafaba L., plants. MO also reduced the longevity and fecundity of young adult A. pisum exposed to MO-treated broad bean. MO was slow-acting against A. pisum. Mortality caused by MO stabilised seven days after newborn A. pisum were exposed to treated broad bean and 10 days for adults. The seven day LC₅₀ for individuals exposed from birth was 27.50 mg azadirachtin liter^?1 while the 10 day LC₅₀ for adults was 53.32 mg liter^?1. Contrary to previous studies suggesting that neem insecticides are not contact toxicants, we found that MO applied topically to adult A. pisum caused effects similar to those found in individuals that fed upon treated plants. However, MO was slower-acting when applied topically. Mortality in adult A. pisum caused by topically applied MO stabilised 17 days after treatment with a resultant LD₅₀of 2.91 μg azadirachtin g^?1.     

The dietary toxicity of flocoumafen to hens: Elimination and accumulation following repeated oral administration

In a dietary toxicity study, laying hens received a diet containing the rodenticide flocoumafen at concentrations of 1.5, 5, 10 and 50 mg kg^?1 for five consecutive days. The LC₅₀ at termination following a 28-day observation period was 16.4 mg kg^?1. Livers of birds which received doses of flocoumafen between 5 and 50 mg kg^?1 had concentrations of flocoumafen (1.5 nmol g^?1) that were independent of dose. The data indicate the presence in hen liver of a saturable high-affinity flocoumafen binding site with similar characteristics and capacity to that of the quail and rat. Residues of flocoumafen in samples of breast and leg muscle were low in all exposure groups. Higher, dose-related residues were found in samples of abdominal fat and skin-associated fat and there was a clear demonstration of the transfer of dose-related residues into eggs. In a separate study in which hens were dosed with [¹⁴C]flocoumafen for five consecutive days at a daily rate of 1 and 4 mg kg^?1 body weight, the majority (68 %) of the daily radioactive dose was eliminated over the following 24 hours via excreta. Residues in liver at death or when killed accounted for < 1 % of the cumulative administered radioactivity. Residues in eggs were located primarily in the yolk with maximum concentrations 1.0 mg kg^?1 or 0.18% of the low dose; 2.1 mg kg^?1 or 0.06% of the high dose as [¹⁴C]flocoumafen equivalents were observed at 10 days after start of dosing. Some 40 % of the total activity in the yolk was unchanged flocoumafen.     

Acaricidal activities of Santolina africana and Hertia cheirifolia essential oils against the two-spotted spider mite (Tetranychus urticae)

BACKGROUND: Many plant essential oils show a broad spectrum of activity against pests. This study investigated the effects of two essential oils on Tetranychus urticae, one of the most serious pests in the world. RESULTS: The chemical composition of the two oils was characterised by GC‐MS. The most abundant component in the Santolina africana (Jord. & Fourr) oil was terpinen‐4‐ol (54.96%), while thymol (61%) was prevalent in the Hertia cheirifolia (L.) oil. Mortality and fecundity were measured upon treatment with oil concentrations ranging from 0.07 to 6.75 mg L^?1 with a Potter spray tower. Mite mortality increased with oil concentration, with LC₅₀ values of 2.35 mg L^?1 for S. africana and 3.43 mg L^?1 for H. cheirifolia respectively. For both oils, a reduction in fecundity was observed at concentrations of 0.07, 0.09 and 0.29 mg L^?1. Artificial blends of constituents of oils were also prepared and tested with individual constituents missing from the mixture. The results showed that the presence of all constituents was necessary to equal the toxicity of the two natural oils. CONCLUSION: S. africana and H. cheirifolia oils can provide valuable acaricide activity with significantly lower LC₅₀ values. Thus, these oils cause important mortality and reduce the number of eggs laid by females. Copyright © 2012 Society of Chemical Industry     

Organosilane insecticides. Part I: Biological and physical effects of isosteric replacement of silicon for carbon in etofenprox and MTI-800

Substitution of silicon for carbon was explored in etofenprox and MTI-800, primarily to establish the suitability of silicon for pesticide construction and to probe steric effects. It was shown that silicon is an effective building block for insecticides with subtle qualitative and quantitative differences relative to the carbon analogs. The silanes were slightly less toxic to insects than the carbon analogs (relative potency of 0.2-0.6) but the silane analog of MTI-800 was considerably less toxic to fish (0% mortality at ≥50 mg liter^?1) than MTI-800 itself (LC₅₀ = 3 mg liter^?1). The mode of action of both carbon and silicon compounds was similar in the intact, electrode-implanted cockroach and involved repetitive firing of a sensory nerve; potency measurements were also made using an in-vitro nerve assay. The possible metabolic and physicochemical contributions to the observed insecticide potencies were explored using synergism studies, physical chemistry measurements and quantum mechanical calculations.     

Quantitative autoradiography of GABA receptors in locust (Schistocerca americana) brain

Conventional film autoradiography was used at the light microscopic level for the localization and quantization of 4-aminobutyric acid (GABA) receptors in the locust brain (Schistocerca americana). Localization of the receptor site was achieved via binding with the receptor-ligand probe [³ H]muscimol. Frozen sections were cut and subsequently incubated either in 40 nM [³H]muscimol or by coincubating sections with [³H]muscimol and one of the following: GABA (50 μM)], a receptor specific agonist [muscimol (1 μM) or isoguvacine (1 μM)], an uptake inhibitor [nipecotic acid (50 μM)], or a noncompetitive channel modulator [avermectin B_1a, (1 μM) or aldrin (50 μM)]. Through computer image enhancement and densitometric analysis of the optical density of [³H]muscimol binding sites, the interaction of the above compounds with the putative GABA receptor was determined for various anatomical regions of the locust brain. By comparing the differently treated, but adjacent sections, GABA receptor distribution was quantitated and mapped. Receptor sites were found distributed in the antennal lobes, central body, β-lobe and β-lobe of the corpus pedunculatum, protocerebral bridge, and calyx as well as the optic lobe regions.     

Being exposed to low concentrations of pirimiphos-methyl and chlorfenapyr has detrimental effects on the mobility of Trogoderma granarium

BACKGROUND

Sublethal effects of insecticides may negatively affect several biological and behavioral traits of insects. The lethal effects of pirimiphos-methyl and chlorfenapyr have been previously showed on Trogoderma granarium, but little knowledge is available about their sublethal effects at low concentrations on both sexes. Herein, the sublethal effects of pirimiphos-methyl and chlorfenapyr on the mobility of T. granarium males and females were investigated.

RESULTS

Lethal concentration (LC) values of pirimiphos-methyl and chlorfenapyr were lower for T. granarium females than males. LC values on males were LC₁₀ = 0.000788 and 0.00139 mg active ingredient (a.i.) cm⁻², LC₃₀ = 0.00350 and 0.00535 mg a.i. cm⁻², and LC₅₀ = 0.00986 and 0.0136 mg a.i. cm⁻² for pirimiphos-methyl and chlorfenapyr respectively. LC on females were LC₁₀ = 0.000704 and 0.00110 mg a.i. cm⁻², LC₃₀ = 0.00323 and 0.00428 mg a.i. cm⁻², and LC₅₀ = 0.00925 and 0.0110 mg a.i. cm⁻² for pirimiphos-methyl and chlorfenapyr respectively. The walking duration of beetles exposed to LC₃₀ of pirimiphos-methyl was significantly lower than the individuals exposed to LC₁₀ and LC₃₀ of both insecticides and control ones. Pirimiphos-methyl LC₃₀-exposed males remained more time on their back (101.7 s) than females (46.9 s), while the latter stayed immobile longer than males (381.7 s versus 371.9 s). The highest speed was recorded for control beetles (14.17 mm s⁻¹ females vs. 12.44 mm s⁻¹ males), while the lowest speed was observed in pirimiphos-methyl LC₃₀-treated males (8.36 mm s⁻¹) and females (9.66 mm s⁻¹).

CONCLUSIONS

Overall, males and females exposed to low concentrations of pirimiphos-methyl and chlorfenapyr showed reduced motility. This knowledge can be exploited further to unlock behavioral effects of insecticides for effective pest management programs in warehouses. © 2023 Society of Chemical Industry.     

新型喜树碱类药性分子的合成与杀螨活性

应用三组分“一锅法”合成了一系列新型喜树碱类药性分子 4a~4n、5a~5n 和 7a~7f ,所有目标化合物均经核磁共振氢谱和质谱确证。室内杀螨活性测定结果表明,所有化合物对朱砂叶螨Tetranychus cinnabarinus均有不同程度的杀螨活性,其中化合物 4l （LC₅₀:25.93 mg/L）和 7d （LC₅₀:28.16 mg/L）的杀螨活性与喜树碱（LC₅₀:24.55 mg/L）的相当。该研究为进一步开展喜树碱作为先导的新农药设计与研究提供了基础。     

The toxicity of brodifacoum wheat bait to the field rodents Microtus guentheri and Meriones tristrami

The toxicity of the anticoagulant brodifacoum to the field rodent species Microtus guentheri (Danford & Alston) and Meriones tristrami Thomas was tested in the laboratory. Brodifacoum 0.05 g kg^?1 whole-wheat bait was offered to the animals without additional food. The LD₅₀ calculated for M. guentheri was 2.28 mg kg^?1 body weight. Brodifacoum was found to be more toxic to M. tristrami; the LD₅₀ was c. 0.8–0.9 mg kg^?1 body weight. The toxicity data served to plan the doses of bait to be broadcast in the field.     

Mode of action of the plant-derived silphinenes on insect and mammalian GABAA receptor/chloride channel complex

The silphinenes are tricyclic sesquiterpenes that have antifeedant and toxic effects in insects and structural similarity to the known GABA antagonist, picrotoxinin. In murine synaptoneurosomes, silphinenes block GABA-stimulated influx of ³⁶Cl⁻ with EC₅₀s in the range of 10-30 μM. In insects, silphinenes were tested in neurophysiological recordings of central neurons from third instar Drosophila melanogaster larvae. Silphinenes reversed the blockage of neuronal firing induced by GABA, but had little effect below 100 μM. The structure-activity profile observed in the murine chloride flux assay was also observed in the larval neurophysiological assay, indicating little selectivity for the silphinenes. A reference silphinene was equally active on nerve preparations from the rdl strain of D. melanogaster, which is resistant to channel-blocking antagonists via an altered GABA receptor. This latter finding suggests that silphinenes interact with the insect GABA receptor in a manner somewhat different from PTX, and that rdl resistance in the field may have little effect on silphinene efficacy.     

Binding Sites for Ca2+-Channel Effectors and Ryanodine in Periplaneta americana—Possible Targets for New Insecticides

The calcium channel and the ‘calcium release channel’ of muscle membrane of the cockroach Periplaneta americana have been characterized. Biological assays with calcium channel blockers and ryanodine on different insects and acari revealed pronounced insecticidal effects with ryanodine, but not with calcium channel blockers, at concentrations between 0·1 and 300 μg ml⁻¹. Skeletal muscle membranes derived either from the tubular network or from the sarcoplasmatic reticulum of P. americana were characterized with respect to the binding of the dihydropyridine (DHP) [³H]isradipine (PN 200-110), the phenyl-alkylamine [³H]verapamil and the alkaloid [³H]ryanodine. Preliminary binding studies with the benzothiazepine [³H]diltiazem suggest a low-affinity binding site with a IC₅₀ value of 3·3 μM . All binding sites tested were sensitive to treatment with proteinase K. Optimal conditions for binding of the radioligand ryanodine revealed the highest specific binding at pH 8 and at calcium chloride concentrations between 100 and 500 μM . EGTA at 10 μM abolished 95% of the ryanodine binding. Binding studies with calcium channel binding sites revealed a pronounced effect of low Ca²⁺ concentrations on specific isradipine binding, whereas verapamil and diltiazem binding were only reduced by the presence of 200 μM EGTA. With respect to high Ca²⁺ concentrations, specific binding of diltiazem, isradipine and verapamil was reduced by 73, 40 and 20%, respectively, at 5 mM Ca²⁺. Radioligand binding experiments showed high-affinity binding sites for ryanodine and isradipine. K_D values of 0·95 nM (B_max=550 fmol mg⁻¹ protein) and 0·75 nM (B_max=213 fmol mg⁻¹ protein) were determined respectively. A lower-affinity binding site was identified in binding studies with verapamil (K_D=7·4 nM and B_max=27 fmol mg⁻¹ protein). [³H]isradipine displacement studies with several dihydropyridines revealed the following ranking of affinity: nitrendipine>isradipine>Bay K8664≪nicardipine. Displacement of [³H]verapamil binding by effectors of the phenylalkylamine binding site showed that bepridil and S(-)verapamil had the highest affinities of the compounds tested followed by (±)verapamil, nor-methylverapamil and R(+)verapamil.     

Disposition kinetics of cypermethrin and fenvalerate in black bengal lactating goats

Disposition kinetics of cypermethrin and fenvalerate were investigated in lactating black Bengal goats following single dose intravenous administration at 57 and 45 mg kg^?1 respectively. The maximum and minimum blood concentrations of cypermethrin were 18.49 (±3.17) and 0.06 (±0.002) μg ml^?1, while the corresponding values for fenvalerate were 14.58 (±2.37) and 0.04 (±0.005) μg ml^?1 respectively. Both cypermethrin and fenvalerate remained present in blood for 36 h. The mean t1/2β) and Vd_area values were 5.56 (±0.28) h and 10.38 (±2.20) litre kg^?1 for cypermethrin and 5.66 (±0.35) h and 11.31 (±2.20) litre kg^?1 respectively for fenvalerate. Both cypermethrin and fenvalerate persisted in goat milk for 36 h. The t1/2β) and AUC values of fenvalerate were 7.37 (±1.84) h and 122.38 (±11.65) μg h ml^?1 whilst the corresponding values for cypermethrin were 6.66 (±1.54) h and 99.48 (±7.81) μg h ml^?1 in milk respectively.