Effects of monoterpenoid insecticides on [H]-TBOB binding in house fly GABA receptor and Cl uptake in American cockroach ventral nerve cord

Monoterpenoids and their derivatives from plant essential oils showed good insecticidal activities in previous studies, but the mechanisms of their action as natural insecticides are not known yet. In the present work, we evaluated the pharmacological action of five monoterpenoids (α-terpineol, carvacrol, linalool, pulegone, and thymol) on native insect GABA receptors from house flies and American cockroaches using radiotracer methods. In the [³H]-TBOB binding assay, carvacrol, pulegone, and thymol all enhanced the [³H]-TBOB binding to membrane preparation of house fly heads with EC₅₀ values of 48 μM, 432 μM, and 6 mM, respectively. Moreover, these three monoterpenoids at concentrations of 500 μM and 1 mM also significantly increased the ³⁶Cl⁻ uptake induced by GABA in membrane microsacs prepared from American cockroach ventral nerve cords. These results revealed that carvacrol, pulegone, and thymol are all positive allosteric modulators at insect GABA receptors. The other two monoterpenoids that were tested, α-terpineol and linalool, showed little or no effect in both the [³H]-TBOB binding and ³⁶Cl⁻ uptake assays.     

Effects of topical and bath applications of the insecticide deltamethrin on electrical activity in a leg mechanoreceptor of the cockroach,Periplaneta americana

Two different methods were used to analyze the effects of topical and bath applications of low concentrations of deltamethrin. The first method enabled the analysis of the receptor potential as well as that of the spike activity generated by mechanical or electrical stimulation of the mechano-receptor. The second method enabled recording of the conducted spike activity originating from a mechanical stimulation of the receptor and propagated along the sensory nerve. Topical application of small amounts of deltamethrin (10⁻⁹ to 10⁻⁷ g) had little effect on the receptor potential induced by mechanical stimulation of the sensory hair but blocked the action potentials within a few minutes. Electrical stimulation of the receptor cell revealed that conduction in the dendrite was affected first by the insecticide. The effects of topical application on conducted activity were compared with those of bath applications (2 × 10⁻⁸ to 2 × 10⁻⁷ M) and no significant difference was found, suggesting a rapid penetration of the insecticide through the cuticle. These effects were not reversible and this absence of reversibility was not correlated with the integrity of the barrier which protects the receptor cell from rapid changes in the ionic composition of the hemolymph. Deltamethrin was never found to induce bursts of activity in the mechanoreceptor cell under investigation either at rest or following mechanical or electrical stimulation. There are, however, some indications that other receptor cells may respond differently to this insecticide.     

Effects of the pyrethroids bioallethrin,deltamethrin and RU-15525 on the electrical activity of a cuticular mechanoreceptor of the cockroach Periplaneta americana

A study has been made of the effects of bioallethrin, RU-15525 [5-benzyl-3-furylmethyl (1R)-cis-2,2-dimethyl-3-(tetrahydro-2-oxo-3-thienylidenemethyl)-cyclopropanecarboxylate, ‘Kadethrin’], and deltamethrin on the electrical activity, measured in vivo, of a cuticular mechanoreceptor of Periplaneta americana. The modifications induced by these pyrethroids on the membrane excitability can be classified into two groups: Type I effects (bioallethrin) are characterised by a substantial increase in the number of action potentials triggered at the initiation site by a given mechanical stimulation, by an electrical activity persisting after mechanical stimulus has been stopped (repetitive activity), and possibly, by an inhibition of excitability of the cell membrane. Type II effects (RU-15525 and deltamethrin), are characterised by an inhibition of the excitability of the initiation site. In the case of RU-15525, there was a transient spontaneous electrical activity. Both types of effects have been linked to an action on the sodium channel, particularly at the initiation site. The preparation studied, which possessed no synapses, was shown to be more sensitive to deltamethrin (which is also the most insecticidal of the three pyrethroids) than to either allethrin or RU-15525. These results suggest that it is unnecessary to envisage a main target (sodium channel) that is different for the two types of pyrethroid.     

Identification of a high-affinity binding site for dinotefuran in the nerve cord of the American cockroach

The binding of the neonicotinoid insecticide dinotefuran to insect nicotinic acetylcholine receptors (nAChRs) was examined by a centrifugation method using the nerve cord membranes of American cockroaches and [3H]dinotefuran (78 Ci mmol-1). The Kd and Bmax values of [3H]dinotefuran binding were estimated to be 13.7 nM and 14.8 fmol 40 microg-1 protein respectively by Scatchard analysis. Epibatidine, an nAChR agonist, showed a rather lower affinity to the dinotefuran binding site (IC50=991 nM) than dinotefuran (IC50=5.02 nM). Imidacloprid and nereistoxin displayed lower potencies than dinotefuran but higher potencies than epibatidine. The potencies of five dinotefuran analogues in inhibiting the specific binding of [3H]dinotefuran to nerve cord membranes were determined. A good correlation (r2=0.970) was observed between the -log IC50 values of the tested compounds and their piperonyl butoxide-synergised insecticidal activities (-log LD50 values) against German cockroaches. The results indicate that a high-affinity binding site for dinotefuran is present in the nerve cord of the American cockroach and that the binding of ligands to the site leads to the manifestation of insecticidal activity.     

Effect of abamectin on electrophysiological activity in the ventral nerve cord of Periplaneta americana L.: Correlation with symptoms of poisoning and levels of toxicant in vivo

Twenty-four hours after injection of adult male Periplaneta americana with 36 ng [5-³H]abamectin, when symptoms of poisoning were apparent in most individuals, similar levels of radioactivity were found in tissue samples from the ventral nerve cord, metathoracic muscle, fat body and testis of randomly-selected insects. When insects injected with [5-³H]abamectin (36 ng) were separated after 24 h into three groups showing varying symptoms, the level of radioactivity in the ventral nerve cord was found to be significantly greater in partially-paralysed and paralysed groups (4- and 7-fold respectively) than in a treated but non- paralysed group. The mean levels of abamectin in the nerve cords of unaffected, ‘partially-paralysed’ and ‘paralysed’ insects were estimated to be 4, 23 and 37 nM respectively. Extracellular studies of the in-vitro action of abamectin (10 nM and 1 μM) on the spontaneous activity of a picrotoxin-sensitive, partially desheathed, ventral nerve cord preparation of adult male P. americana found the mean response time to be relatively slow (77 and 38 min respectively). In sheathed nerve cords, the mean response time to abamectin (1 μM) was 117 min. In all cases, treatment with abamectin increased the stimulus voltage required to evoke a response. Spontaneous activity was found to be progressively reduced in ventral nerve cord preparations from ‘partially-paralysed’ and ‘paralysed’ insects compared with ‘non-paralysed’ and untreated insects following dissection 24 h after injection of P. americana with unlabelled or labelled abamectin (36 ng), while the stimulus required to evoke activity in the ventral nerve cord showed the reverse trend. These differences in electrophysiological activity could be correlated directly with varying levels of abamectin in the nerve cords of ‘paralysed’ and ‘partially-paralysed’ insects.     

Comparative activity of tralomethrin and deltamethrin on Periplaneta americana

Tralomethrin, a tetrabromopyrethroid pesticide, is sometimes considered as owing its activity only to its degradation into deltamethrin. This work provides new results showing the activity of tralomethrin itself on Periplaneta americana. Behavioral study during tarsal contact shows that at low doses, tralomethrin is more potent than deltamethrin. Residue analysis shows that after topical application, the observed activity cannot be explained by the residues of deltamethrin present with tralomethrin. We also show that under our conditions, there is no degradation of tralomethrin on the insects' cuticle and the toxic effect cannot be explained by the quantities of deltamethrin found inside the intoxicated insects.     

Cartap activity on the cockroach nervous and neuromuscular transmission

By employing intracellular electrodes on the 6th abdominal ganglion, Cartap hydrochloride 10^?5M caused in all experiments a block of the provoked stimulus transmission and a decrease of the cell membrane resting potential; the giant fiber conduction was not affected. In the experiments with extracellular electrodes Cartap 10^?5M provoked a marked increase of the spontaneous activity followed by block which partially disappeared after washing. The same effects were obtained on spontaneous activity when Cartap 10^?5M was used on the denervated 6th abdominal ganglion and in experiments conducted at 0 Ca²⁺ or at 20 mM Mg²⁺. Cartap 10^?5M did not affect the response to direct or indirect stimulation of cockroach neuromuscular preparation. These results tend to confirm that Cartap affects the postsynaptic region of the ganglionic nervous junction. The possible cause of the resting potential decrease is also discussed.     

Effects of deltamethrin on hematological parameters and enzymatic activity in Ancistrus multispinis (Pisces, Teleostei)

Deltamethrin (DM) is a pyrethroid insecticide widely used in Brazilian crops and in pest-control programs because of its low environmental persistence and toxicity. It has been shown to exert a wide range of effects on non-targeted organisms including fishes. The aim of this study to evaluate the effects of deltamethrin through the hematological and biochemical parameters using Ancistrus multispinis as animal model. First, blood of A. multispinis was collected by cardiac puncture in order to evaluate the basal values of the total cell counts, hemoglobin and hematocrit rates. A. multispinis showed low number leukocytes, red blood cells and hemoglobin compared to other species. The intoxication with DM (0.1 or 0.3 mg kg⁻¹) induced leukocytosis and increases the number of erythrocytes and hemoglobin levels 96 h after the injection when compared to vehicle-injected animals. The injection of lipopolysaccharide (LPS) also induced a significant leukocytosis and increased the erythrocytes number 4 h after the injection. The combination of the higher dose of DM with LPS showed an additional effect in the number of leukocytes and erythrocytes. The GST and EROD activities were also evaluated in the gills and liver, respectively, 96 h after intoxication with both doses of DM. The GST activity decreased after DM intoxication in both doses while EROD activity was not significantly different. These results suggest that A. multispinis is a valuable model for ecotoxicological studies. Also, DM can affect the metabolizing system (GST) and immunologic system of A. multispinis, a condition that can be worsened in the presence of inflammation or infection.     

溴氰菊酯对南方小花蝽捕食番茄潜叶蛾能力的影响

为探究溴氰菊酯对南方小花蝽Orius similis捕食番茄潜叶蛾 Tuta absoluta能力的影响,本研究以溴氰菊酯对南方小花蝽的致死中浓度为处理浓度,采用药膜法处理南方小花蝽成虫,然后让存活的南方小花蝽取食番茄潜叶蛾卵及1龄幼虫,分析溴氰菊酯对其捕食功能反应及捕食行为的影响。结果表明,经致死中浓度的溴氰菊酯处理后,南方小花蝽捕食番茄潜叶蛾的能力及行为均受到影响,功能反应模型仍符合Holling Ⅱ模型,但南方小花蝽处理猎物的时间延长,控害效能降低,搜寻效应下降, 成虫对卵和1龄幼虫的日最大捕食量分别下降了47.37粒/皿、9.47头/皿;而处理1粒番茄潜叶卵和1头1龄幼虫所用的时间分别延长了777.6 s和3 456.0 s,同时南方小花蝽搜寻、行走、捕食番茄潜叶蛾卵的行为时间分别缩短了444.2、750.2、919.6 s,静止和梳理时间则分别延长了1 677.6、403 s,对番茄潜叶蛾卵和1龄幼虫的捕食量分别降低了4头和1头。因此,溴氰菊酯对南方小花蝽捕食能力产生了抑制作用,在田间防控番茄潜叶蛾时应延长溴氰菊酯与南方小花蝽使用的间隔时间,更好地协调化学与生物防治。     

Effects of DDT on the cockroach nervous system at three temperatures

Some effects of DDT on the cockroach nervous system have been correlated with poisoning symptoms, using free-walking cockroaches with implanted electrodes. Experiments at 16.5°C and 32°C used LD₉₅ doses and at 25°C, an estimated LD₉₅. DDT had excitant actions on each nerve studied; cercal afferent and efferent neurones, and abdominal interneurones. The effects on the central nervous system became more marked as temperature was reduced, despite the smaller quantity of DDT employed, but the excitant actions on the peripheral nervous system were not quantified. It is suggested that the effects of DDT on the cockroach nervous system could account for the negative temperature coefficient of toxicity of DDT.     

Action of cismethrin and deltamethrin on functional attributes of isolated presynaptic nerve terminals from rat brain

Isolated presynaptic nerve terminals (synaptosomes) prepared from rat brain were used to evaluate the actions of a tremor (T)-syndrome (cismethrin) and a choreoathetosis-salivation (CS)-syndrome (deltamethrin) pyrethroid on the functional attributes of synaptosomes by measuring calcium influx and endogenous neurotransmitter (l-glutamate) release with fluorescent assays. Both cismethrin and deltamethrin stimulated calcium influx, however, only deltamethrin enhanced Ca²⁺-dependent neurotransmitter release and its action was stereospecific, concentration-dependent, stimulated by depolarization, unaltered by tetrodotoxin, and blocked by ω-conotoxin GVIA. Our results delineate a separate action of deltamethrin on presynaptic nerve terminals from that elicited by cismethrin and implicate Ca_v2.2 calcium channels as target sites for deltamethrin that is consistent with the observed in vivo release of neurotransmitter at the onset of convulsive symptom caused by CS-syndrome pyrethroids. This information will allow a more complete understanding of the molecular and cellular nature of pyrethroid-induced neurotoxicity and expands our knowledge of the structure–activity relationships of pyrethroids in regards to their action on voltage-sensitive calcium channels.     

Circadian dynamics of locomotor activity and deltamethrin susceptibility in the pine weevil,Hylobius abietis

Rhythmic locomotor activity and daily susceptibility to deltamethrin were tested in the pine weevil,Hylobius abietis (L.) (Coleoptera, Curculionidae), a pest of young conifer plants. In constant darkness, beetles revealed a free-running circadian pattern of locomotor activity (average period 22h : 20min). Under long photoperiod, L:D 18:6, entrainment of motor activity was observed. In the entrained population of the weevils, a peak of locomotor activity occurred at about the beginning of the dark phase, and the minimum occurred in the middle of the light phase. Fluctuations of susceptibility to a standard dose of deltamethrin (0.5 μg/g body weight) varied across the day, and were inversely correlated to the changes in locomotor activity. The importance of considering the daily organization of insect biology in studying insect resistance to pesticides is re-emphasized. 3 www.csa.com. The following databases were screened: Animal Behaviour Abstracts, AGRICOLA, Aquatic Science and Fishery Abstracts, Biological Sciences, Ecology Abstracts, Entomology Abstracts, Environmental Science and Pollution Abstracts, Health and Safety Science Abstracts, Pollution Abstracts, Water Resource Abstracts, Toxicology Abstracts, TOXLINE.     

Inactivation of deltamethrin on stored wheat

Residues of deltamethrin on wheat grain of 12% moisture content, stored in the laboratory at 25°C, remained constant within experimental error over a 15-month interval. However, the biological activity of the residues against Sitophilus oryzae (L.) declined to 78% of the initial value at 3 months, and to 65% at 15 months after application. Inactivation of a proportion of the intact residues is indicated.     

Effect of thiamethoxam on cockroach locomotor activity is associated with its metabolite clothianidin

BACKROUND: In the present study, the effect of thiamethoxam and clothianidin on the locomotor activity of American cockroach, Periplaneta americana (L.), was evaluated. Because it has been proposed that thiamethoxam is metabolised to clothianidin, high‐performance liquid chromatography coupled with mass spectrometry was used to evaluate the amount of clothianidin on thiamethoxam‐treated cockroaches. RESULTS: One hour after neonicotinoid treatment, the time spent in the open‐field‐like apparatus significantly increased, suggesting a decrease in locomotor activity. The percentage of cockroaches displaying locomotor activity was significantly reduced 1 h after haemolymph application of 1 nmol g^?1 neonicotinoid, while no significant effect was found after topical and oral administration. However, at 24 and 48 h, all neonicotinoids were able to reduce locomotor activity, depending on their concentrations and the way they were applied. Interestingly, it was found that thiamethoxam was converted to clothianidin 1 h after application, but the amount of clothianidin did not rise proportionately to thiamethoxam, especially after oral administration. CONCLUSION: The data suggest that the effect of thiamethoxam on cockroach locomotor activity is due in part to clothianidin action because (1) thiamethoxam levels remained persistent 48 h after application and (2) the amount of clothianidin in cockroach tissues was consistent with the toxicity of thiamethoxam. Copyright © 2010 Society of Chemical Industry     

Cholinergic properties of pinched-off synaptic nerve endings from the central nervous system of the cockroach Periplaneta americana

The preparation and cholinergic properties of a subcellular fraction, enriched in pinched-off nerve-endings (synaptosomes) from the central nervous system of the cockroach Periplaneta americana, are described. The endings retained their cytoplasmic components, as shown by the presence of marker enzymes and by ultrastructural examination. A carrier-mediated, high-affinity uptake of [³H] choline into the synaptosomes was demonstrated, and this uptake was saturable, depended on a Na⁺-gradient, and was inhibited by hemicholinium-3. It had an apparent K_m value of 0.6 (±0.1) μM, and a V_max of 20.5 (±2.5) pmol min^?1 per mg of protein. The high-affinity [³H]choline uptake was associated with the synthesis of [³H]phosphocholine and [³H]O-acetylcholine. The rate of [³H]choline uptake in synaptosomes was increased by DDT [1,1,1-trichloro-2,2-bis(4-chlorophenyl) ethane] at 100 nM concentration, and this increase was inhibited by tetrodotoxin, while neostigmine appeared to be a potent inhibitor (I₅₀ = 10 pM) of the DDT-activated uptake of [³H]choline. The site of action of the insecticides was specifically on the pre-synaptic nerve terminals because the synaptosomes preparation did not retain the post-synaptic membrane of the original nerve-endings. Cockroach synaptosomes provided a useful in-vitro preparation for studying the effects of insecticides on the pre-synaptic nerve endings.     

Interaction of dinotefuran and its analogues with nicotinic acetylcholine receptors of cockroach nerve cords

To investigate the action of dinotefuran (MTI-446, 1-methyl-2-nitro-3-(tetrahydro-3-furylmethyl)guanidine), a recently developed insecticide, on insect nicotinic acetylcholine receptors (nAChRs), we determined the potencies of the compound and 15 analogues in inhibiting the specific binding of [3H]epibatidine (EPI), a nAChR agonist, and [3H]alpha-bungarotoxin (alpha-BGT), a competitive nAChR antagonist, to the nerve cord membranes of American cockroaches (Periplaneta americana). Racemic dinotefuran inhibited [3H]EPI binding with an IC50 of 890 nM and [3H]alpha-BGT binding with an IC50 of 36.1 microM. Scatchard analysis indicated that the dinotefuran inhibition of [3H]EPI binding was a competitive one. Slight structural modification caused a drastic reduction in potency; only four analogues were found to be equipotent to or more potent than dinotefuran. Chloropyridinyl and chlorothiazolyl neonicotinoid insecticides displayed two or three orders of magnitude higher potency than dinotefuran. There was a good correlation between the IC50 values of tested compounds obtained with [3H]EPI and those obtained with [3H]alpha-BGT. A better correlation was observed between 3-h knockdown activities (KD50) against German cockroaches (Blattella germanica) and IC50 values obtained from [3H]EPI assays than between 24-h lethal activities (LD50) and IC50 values. While the results indicate that dinotefuran and its analogues interact with the ACh-binding site in cockroach nAChRs, it remains to be elucidated why they displayed lower potencies than those expected based on their insecticidal activities.     

Symptoms of mirex,dieldrin, and DDT poisoning in the field cricket,Gryllus pennsylvanicus burmeister,and effect on activity of the central nerve cord

In the field cricket, Gryllus pennsylvanicus, the characteristic feature of mirex poisoning was the long latent period of at least 72 hr followed by hyperactivity, ataxia, and convulsions and paralysis. Dieldrin poisoning showed a short latent period followed directly by ataxia and convulsions and paralysis. The stages of DDT poisoning were locomotor instability, ataxia and convulsions and paralysis followed by death.Increased spontaneous activity of the central nerve cord in the initial stages of poisoning was characteristic for all three insecticides. DDT poisoned crickets showed DDT-type trains or groups of spikes in the central nerve cord during ataxia and early convulsions, but no synaptic after-discharges were observed at any stage of poisoning. Dieldrin and mirex poisoned crickets did not show DDT-type trains but a prolonged synaptic after-discharge was evident in the early stages of poisoning. In mirex poisoned crickets the increased spontaneous activity and the synaptic after-discharge was more acute than for dieldrin.     

Evidence for different mechanisms of action of the three pyrethroids,deltamethrin, cypermethrin,and fenvalerate,on the excitation threshold of myelinated nerve

The effects of three α-cyano pyrethroids (deltamethrin, fenvalerate, and cypermethrin) on the electrophysiological function of single myelinated nerve fibers from Rana esculenta were investigated. The time course of pyrethroid-induced changes on the threshold interval, V_s − V_m (V_s: threshold voltage; V_m: membrane potential), as well as stationary membrane parameters determining this interval was measured on the same nerve preparation (membrane potential V_m, stationary transition voltage V_Tr, stationary sodium conductance). The results suggest that the mechanisms of changing the threshold interval are different for the three pyrethroids. Deltamethrin and cypermethrin increase this interval until inexcitability, deltamethrin by increasing the stationary sodium conductance and cypermethrin by blocking the sodium conductance. Fenvalerate, however, insignificantly affects the threshold interval because both V_m and V_s are shifted parallel by about the same amount in the same direction (depolarization). These qualitatively different effects of chemically related substances differentiate the pyrethroids from other classes of substances which are effective on the nerve function and suggests that the molecular mechanisms underlying the pyrethroid effects might have a unique quality.     

Field assessment of the effects of deltamethrin on polyphagous predators in winter wheat

In the south-west of England, cereal aphids can spread barley yellow dwarf virus and reproduce during winter. Ground-living polyphagous predators may be important in controlling these active cereal aphids. This 2-year study investigated the effect of deltamethrin on predator numbers, using pitfall traps. A randomised block design was used in an area of winter wheat (cv. Aquilla) in which deltamethrin-treated and control plots were surrounded by polyethylene barriers. Pitfall catches of polyphagous predators were reduced by about 30% in the treated plots compared with the control plots.     

亚致死剂量溴氰菊酯对亚洲玉米螟雄蛾性信息素通讯行为的影响

用亚致死剂量溴氰菊酯处理亚洲玉米螟雄蛾后,存活雄蛾对信息素定向行为反应受到较大的影响。雄蛾的起飞潜伏期延长,不应率增加,到达诱芯率大幅度下降。反应下降程度与剂量的相关性显著。以雄蛾的行为反应率机率值(Z)对药剂处理剂量对数(X)和处理天数(Y)进行二元回归分析,回归方程分别为:起飞:Z=6.979-6.559X 0.162Y;定向:Z=5.258-2.611X-0.039Y;逆飞:Z=4.982-2.457X-0.061Y;到达:Z=3.399-1.011X 0.168Y。