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PubMed2001

Toxicity and nicotinic acetylcholine receptor interaction of imidacloprid and its metabolites in Apis mellifera (Hymenoptera: Apidae).

Acute oral and contact toxicity tests of imidacloprid, an insecticide acting agonistically on nicotinic acetylcholine receptors (nAChR), to adult honeybees, Apis mellifera L var carnica, were carried out by seven different European research facilities. Results indicated that the 48-h oral LD50 of imidacloprid is between 41 and > 81 ng per bee, and the contact LD50 between 49 and 102 ng per bee. The ingested amount of imidacloprid-containing sucrose solution decreased with increasing imidacloprid concentrations and may be attributed to dose-related sub-lethal intoxication symptoms or to antifeedant responses. Some previously reported imidacloprid metabolites occurring at low levels in planta after seed dressing, i.e. olefine-, 5-OH- and 4,5-OH-imidacloprid, showed lower oral LD50 values (> 36, > 49 and 159 ng per bee, respectively) compared with the concurrently tested parent molecule (41 ng per bee). The urea metabolite and 6-chloronicotinic acid (6-CNA) exhibited LD50 values of > 99,500 and > 121,500 ng per bee, respectively. The pharmacological profile of the [3H]imidacloprid binding site in honeybee head membrane preparations is consistent with that anticipated for a nAChR. IC50 values for the displacement of [3H]imidacloprid by several metabolites such as olefine, 5-OH-, 4,5-OH-imidacloprid, urea and 6-CNA were 0.45, 24, 6600, > 100,000, and > 100,000 nM, respectively. Displacement of [3H]imidacloprid by imidacloprid revealed an IC50 value of 2.9 nM, thus correlating well with the observed acute oral toxicity of the compounds in honeybees. Neurons isolated from the antennal lobe of A mellifera and subjected to whole-cell voltage clamp electrophysiology responded to the application of 100 microM acetylcholine with a fast inward current of between 30 and 1600 pA at -70 mV clamp potential. Imidacloprid and two of the metabolites (olefine- and 5-OH-imidacloprid) acted agonistically on these neurons, whereas the others did not induce currents at test concentrations up to 3 mM. The electrophysiological data revealed Hill coefficients of approximately 1, indicating a single binding site responsible for an activation of the receptor and no direct cooperativity or allosteric interaction with a second binding site.

Animals↗
PubMed2001

Insecticidal and binding activities of N3-substituted imidacloprid derivatives against the housefly Musca domestica and the alpha-bungarotoxin binding sites of nicotinic acetylcholine receptors.

N3-substituted imidacloprid congeners containing C1-C6 alkyl groups or various analogous groups, and their corresponding nitromethylene analogues, were used in this study. Their insecticidal activity against the housefly, Musca domestica, and their binding activity toward the nicotinic acetylcholine receptor were determined. The insecticidal test was conducted using the synergists piperonyl butoxide and propargyl propyl phenylphosphonate. The binding assay was performed with housefly head membrane preparations using radio-labelled alpha-bungarotoxin. Both insecticidal and binding activities were drastically lowered by the introduction of alkyl/allyl groups at the imidazolidine NH sites of both nitroimino and nitromethylene compounds. The binding activity of N3-substituted nitromethylene analogues was much higher than that of the corresponding nitroimino analogues. However, the insecticidal activity of both series of compounds with a given substituent was nearly identical. The insecticidal activity correlated positively with the binding activity after taking into account the structural difference of the nitroimino and nitromethylene moieties and a structural feature of the N3-substituents.

Animals↗
PubMed2002

New developments in insecticide resistance in the glasshouse whitefly (Trialeurodes vaporariorum) and the two-spotted spider mite (Tetranychus urticae) in the UK.

A recent survey of insecticide resistance in two of the most problematic pests in UK glasshouses revealed some new developments. At least some individuals in all UK samples of Trialeurodes vaporariorum that were tested resisted the insect growth regulator (IGR) buprofezin. The most strongly resistant strains were unaffected by the field application rate of this compound, and even samples from populations that had never been exposed to buprofezin contained individuals that survived the highest concentration applied (10,000 mg litre-1). The field rate of buprofezin was shown to select for resistance through vapour action alone. The benzophenylurea teflubenzuron, an unrelated IGR, was cross-resisted by buprofezin-resistant individuals. There was no evidence of resistance to imidacloprid, but all T vaporariorum strains tested, regardless of origin, exhibited a high innate tolerance to nicotine, when compared with another whitefly species, Bemisia tabaci. Marked resistance to fenbutatin oxide and tebufenpyrad was found in single glasshouse populations of Tetranychus urticae, but these compounds and abamectin appeared to remain highly effective against all other strains collected.

Acari↗
PubMed2002

The relative toxicities of insecticides to earthworms of the Pheretima group (Oligochaeta).

An artificial soil test was used to determine the LC50 values of carbaryl, chlorpyrifos, imidacloprid, cyfluthrin and fipronil against earthworms of the Pheretima group. For a 24-h interval, carbaryl was the most toxic to earthworms (LC50 = 77 mg kg-1), followed by imidacloprid (155 mg kg-1), cyfluthrin (351 mg kg-1), chlorpyrifos (390 mg kg-1) and fipronil (> 8550 mg kg-1) as the least toxic. For the 48-h and 7-day intervals, imidacloprid was the most toxic to earthworms (LC50 = 5 mg kg-1 and 3 mg kg-1 respectively), followed by carbaryl (16 mg kg-1; 9 mg kg-1), cyfluthrin (128 mg kg-1; 110 mg kg-1), chlorpyrifos (330 mg kg-1; 180 mg kg-1) and the least toxic was fipronil (> 8550 mg kg-1 both intervals). The surface application rates required to achieve these values are compared with the rates recommended for the control of turfgrass pests.

Animals↗
PubMed2002

Nicotinic acetylcholine receptor binding of imidacloprid-related diaza compounds with various ring sizes and their insecticidal activity against Musca domestica.

Fifteen 5-substituted 1-(6-chloro-3-pyridylmethyl)-2-nitromethylene-1,3- diazacyclohexanes and three other related compounds having a five- or seven-membered ring were synthesized and their biological activities were measured in vivo and in vitro. The insecticidal (in vivo) activity was evaluated against houseflies Musca domestica L under synergistic conditions with propargyl propyl phenyl phosphonate and piperonyl butoxide. The binding activity of each compound to nicotinic acetylcholine receptor in vitro was measured using [125I] alpha-bungarotoxin. The insecticidal activities of the unsubstituted diazacyclohexane analogues were slightly higher than those of the imidazolidine analogues, but the enlargement of ring size to diazacycloheptane lowered the activity. Substitution of 1,3-diazacyclohexane or imidazolidine rings was not generally favourable for the activity, but the unsubstituted 1,3-diazacyclohexane analogue showed the highest binding activity. Ring substitutions and ring enlargement decreased the activity 100-30,000-fold.

Animals↗
PubMed2002

Structural effects of dinotefuran and analogues in insecticidal and neural activities.

The insecticidal potencies of dinotefuran and analogues against the adult male American cockroach, Periplaneta americana (L) were measured by injection with or without metabolic inhibitors. The potency of dinotefuran was close to those of clothianidin and imidacloprid under the conditions used. The nerve-excitatory and nerve-blocking activities were measured with central nerve cords of P americana. The nerve-excitatory activity of dinotefuran was lower than that of imidacloprid, but was comparable with that of clothianidin. The nerve-blocking activity of dinotefuran was comparable with that of imidacloprid and slightly higher than that of clothianidin. Quantitative analyses showed that variations in the insecticidal activity were better correlated with variations in the nerve-blocking activity than with those in the nerve-excitatory activity when the contribution of the hydrophobic factor was allowed for.

Animals↗
PubMed2002

Effects of formulation on the run-off of imidacloprid from turf.

Imidacloprid is a pesticide often used to control insect pests on residential lawns and golf courses. To investigate its potential to be transported into non-target aquatic systems by rainfall events, imidacloprid was applied as 5.0 g kg-1 GR and 750 g kg-1 WP to 12 plots planted with bermuda grass set on a 5% slope. The dimethylamine salt of the herbicide 2,4-D was applied simultaneously to the plots in order to normalize the results to prior trials conducted with other pesticides. At a rate of 2.5 cm h-1, 5-cm rainfall events were simulated at 24 and 48 h after application and 2.5-cm events were simulated at 96 and 192 h. After each event water was collected from each plot and analyzed by HPLC for residual insecticide or herbicide. Approximately 1.4% of the insecticide formulated as WP and 1.9% of that formulated as GR was lost from the plots after four run-off events. Of the total mass lost, 64% and 30% respectively occurred in the first and second run-off events for the WP formulation versus 75% and 20% for the GR formulation. These values compare with a total mass export of 2.6% for 2,4-D, of which 95% and 4% of the loss occurred respectively in the first and second run-off events. The maximum concentration of imidacloprid detected in run-off water was 0.49 mg litre-1 and occurred during the first run-off event.

2,4-Dichlorophenoxyacetic Acid↗
PubMed2003

Field relevance of a synergistic effect observed in the laboratory between an EBI fungicide and a chloronicotinyl insecticide in the honeybee (Apis mellifera L, Hymenoptera).

It had been found earlier that the chloronicotinyl insecticide thiacloprid (as the 480 g litre(-1) SC Calypso) poses a favourably low toxicity hazard to the honeybee, Apis mellifera L. As with pyrethroids, the metabolization of chloronicotinyl compounds involves monooxygenases, which are known to be inhibited by some ergosterol biosynthesis inhibitor (EBI) fungicides potentially co-applied with these insecticides. The potential synergistic enhancement of the toxicity of thiacloprid to honeybees when co-applied with such fungicides was therefore studied under laboratory and semi-field conditions. Fungicides of other chemical classes were also examined for synergistic potential to reveal other metabolic interactions. In the laboratory, only a slight synergistic effect was observed with the anilinopyrimidine fungicide examined, while a significant enhancement of thiacloprid toxicity to honeybees was found with EBI fungicides. In three tunnel tests conducted under different environmental conditions to simulate field exposure, no increased mortality was observed when honeybees were directly sprayed with thiacloprid (Calypso) alone or in combination with the EBI fungicide tebuconazole (250 g litre(-1) EW, Folicur). There was also no synergized reduction in the foraging intensity on the treated crop. In general, the foraging intensity decreased after thiacloprid treatment but was restored within 24-48 h. The hive vitality was not affected by either thiacloprid or its tank mix with tebuconazole. Our results suggest that, at the recommended use rates, thiacloprid poses a negligible lethal risk to honeybees when applied either alone or in tank mixes with fungicides of various chemical classes.

Animals↗
PubMed2003

Learning performances of honeybees (Apis mellifera L) are differentially affected by imidacloprid according to the season.

To establish the sublethal concentrations domain, acute and chronic oral tests were conducted on caged honeybee workers (Apis mellifera L) using imidacloprid and a metabolite, 5-OH-imidacloprid, under laboratory conditions. The latter showed a 48-h oral LD50 value (153 ng per bee) five times higher than that of imidacloprid (30 ng per bee). Chronic feeding tests indicated that the lowest observed effect concentrations (LOEC) of imidacloprid and of 5-OH-imidacloprid on mortality of winter bees were 24 and 120 microg kg(-1) respectively. Behavioural effects of imidacloprid and 5-OH-imidacloprid were studied using the olfactory conditioning of proboscis extension response at two periods of the year. Winter bees surviving chronic treatment with imidacloprid and 5-OH-imidacloprid had reduced learning performances. The LOEC of imidacloprid was lower in summer bees (12 microg kg(-1)) than in winter bees (48 microg kg(-1)), which points to a greater sensitivity of honeybees behaviour in summer bees, compared to winter bees.

Animals↗
PubMed2003

Relative effects of the insecticide thiamethoxam on the predator Podisus nigrispinus and the tobacco whitefly Bemisia tabaci in nectaried and nectariless cotton.

The predaceous stinkbug Podisus nigrispinus (Dallas) (Heteroptera: Pentatomidae) feeds on plants as well as on arthropod prey. The question arises whether feeding on plants might expose the predator to systemic insecticide via ingestion of the active ingredient or its metabolites through plant sap of treated plants. This interaction was investigated with nectaried and nectariless cotton plants cropped in pots and treated with the systemic insecticide thiamethoxam at 0.5, 1.0 and 2.0 mg per plant as a root drench. Development of P. nigrispinus fed on prey and on treated nectaried and nectariless cotton plants and confined at 15, 30 and 45 days after insecticide application, and adult reproduction from nymphs caged 30 days after treatment were determined. Podisus nigrispinus life history traits were unaffected by the type of cotton plant, nectaried or nectariless, but were significantly affected by insecticide dose and time after application. Developmental time was extended and fresh adult body weight was reduced by feeding on prey and treated plants. Nymphs caged on treated plants with the highest thiamethoxam concentration at 15 days after application produced only 13.2% of adults. Females emerged from nymphs caged on both plants and at all thiamethoxam concentrations at day 30 after application presented similar reproductive characteristics, except for age of first oviposition, which was delayed on plants treated with the highest thiamethoxam concentration. Thiamethoxam at 0.5 mg per plant restrained tobacco whitefly, Bemisia tabaci Gennadius (Homoptera: Aleyrodidae) colonization only during the first 15 days after application to either cotton plant, and similar immature densities were sampled at day 35 after application on treated and untreated plants. However, plants treated with 1.0 and 2.0 mg per plant as a drench and cropped in pots were protected from tobacco whitefly for up to 45 days after exposure to a whitefly colony.

Animals↗
PubMed2003

Biochemical study of resistance to imidacloprid in B biotype Bemisia tabaci from Guatemala.

Systemic uptake bioassays using excised cotton leaves confirmed resistance to imidacloprid in a Guatemalan population of the tobacco whitefly Bemisia tabaci Gennadius. Polyacrylamide gel electrophoresis of naphthyl esterases identified the insects as B-types. Upon collection from the field, resistance was determined to be 58-fold relative to a susceptible strain originating in the Imperial Valley of California. Resistance levels increased to 126-fold in this population during its continuous exposure to systemically treated cotton. In biochemical investigations, there was no detectable NADPH-dependent mixed function oxidase metabolism of 14C-imidacloprid at any time during the selection process. In contrast, microsomal preparations from housefly abdomens readily produced significant amounts of the mono-hydroxy and olefin derivatives of the parent compound. Detoxification of imidacloprid by housefly MFOs may account for reports of lower toxicity of the insecticide towards this insect compared with whiteflies, despite similar binding properties between imidacloprid and the nicotinic acetylcholine receptors in both species.

Animals↗
PubMed2003

Monitoring of insecticide resistance in damson hop aphid, Phorodon humuli Schrank (Hemiptera: Aphididae) from German hop gardens.

The damson hop aphid, Phorodon humuli (Schrank) (Hemiptera: Aphididae), is one of the most important sucking pests of many hop-growing areas world-wide. In this study we determined the efficacy of several insecticides against strains collected throughout the year 2001. All strains were collected in different hop gardens in the Hallertau (Bavaria), Germany, the largest hop-growing area of the world. First of all we established a leaf dip bioassay, carried out using six-well tissue culture plates and appropriate for monitoring susceptibility against imidacloprid, oxydemeton-methyl, cyfluthrin, amitraz, pymetrozine and pirimicarb. Four of these compounds, imidacloprid, cyfluthrin, pymetrozine and amitraz, are currently registered for the control of sucking pests in German hop gardens and are useful against P. humuli. The leaf-dip bioassay system turned out to be very reliable and robust. Ten P. humuli strains were collected in May 2001 and maintained in the laboratory to assess their resistance to the different insecticides in comparison with two laboratory reference strains (H2 and H5). Using diagnostic concentrations, resistance monitoring for imidacloprid and cyfluthrin was investigated during July and August 2001 on 53 populations from 30 sites around the Hallertau, an area of ca 2500 km2. Resistance to diagnostic concentrations (LC95 for reference strains) of imidacloprid, amitraz and pymetrozine was not detected in any strain received in 2001, but late-season (August) populations seemed to respond more heterogeneously than those collected mid-season (July). Overall composite mean mortalities to diagnostic concentrations of imidacloprid (13 mg litre(-1)) in collections from May, July and August were 95 (+/-2.5), 98 (+/-2.3) and 87 (+/-5.9)%, respectively. Moderate resistance to pyrethroids was observed in all strains collected in May and August using a diagnostic concentrations of 10 mg litre(-1) cyfluthrin (LC95 of the susceptible reference strain H5). Slight to moderate resistance to diagnostic concentrations of oxydemeton-methyl and pirimicarb was observed in some, but not all, strains collected early season. The results are discussed in terms of the implemention of hop aphid resistance management strategies in German hop-cultivation areas.

Animals↗
PubMed2003

Insecticidal activity and nicotinic acetylcholine receptor binding of dinotefuran and its analogues in the housefly, Musca domestica.

The insecticidal activity of dinotefuran and 23 related compounds against the housefly, Musca domestica (L) was measured by injection with metabolic inhibitors. Dinotefuran was less active than imidacloprid and clothianidin by a factor of 10 in molar concentrations. Their binding activities to the fly-head membrane preparation were measured by using [125I]alpha-bungarotoxin ([125I]alpha-BGTX) and [3H]imidacloprid ([3H]IMI) as radioligands. The activity of some selected compounds measured with [3H]IMI was 10(4)-fold higher than that measured with [125I]alpha-BGTX. With [3H]IMI as a radioligand, dinotefuran was 13-fold less active than imidacloprid. The inhibitory effect of dinotefuran on the binding of [3H]IMI to the membrane preparation was in a competitive manner. Quantitative analysis of the insecticidal activity of the test compounds with the binding activity measured with [3H]IMI showed that the higher the binding activity, the higher was the insecticidal activity.

Animals↗
PubMed2003

The potential removal of imidacloprid from water by heat-treated kerolites.

The adsorption of imidacloprid [1-(6-chloro-3-pyridinylmethyl)-N-nitroimidazolidin-2-ylideneamine] on heat-treated kerolite samples at 110 degrees C (K-110), 200 degrees C (K-200), 400 degrees C (K-400) and 600 degrees C (K-600) from pure water solution at 25 degrees C has been studied. The evolution of the surface properties of the kerolite samples, such as specific surface area and porosity, after heat treatment were analysed. The clays were characterised by using FTIR spectroscopy, X-ray diffraction, thermogravimetric and differential thermogravimetric analysis, surface analysis and Hg porosimetry. The experimental adsorption data points were fitted to the Freundlich equation in order to calculate the adsorption capacities (Kf) of the samples; Kf values ranged from 242 mg kg(-1) for the K-110 sample to 1005 mg kg(-1) for the K-600 sample. The values obtained for the removal efficiency (R) ranged from 62.8% for K-110 to 87.2% for K-600. The adsorption experiments showed that the stronger the heat treatment, the more effective was the adsorption of imidacloprid from pure water. This work shows the potential use of heat-activated kerolite for the removal of imidacloprid from environmental waters and drinking water resources.

Adsorption↗
PubMed2003

Selection for imidacloprid resistance in Nilaparvata lugens: cross-resistance patterns and possible mechanisms.

A field population of brown planthoppers (Nilaparvata lugens Stål) was collected and selected for imidacloprid resistance in the laboratory. The resistance increased by 11.35 times in 25 generations and the resistance ratio reached 72.83 compared with a laboratory susceptible strain. The selected resistant strain showed obvious cross-resistance to all the acetylcholine receptor targeting insecticides tested (monosultap 1.44-fold, acetamiprid 1.61-fold, imidacloprid homologues JS599 2.46-fold and JS598 3.17-fold), but not to others. Further study demonstrated that TPP and DEM had no synergism on imidacloprid. However, PBO displayed significant synergism in some different strains, and the synergism increased with resistance (S strain 1.20, field population 1.43 and R strain 2.93). PBO synergism to cross-resistant insecticides was also found in the resistant strain (monosultap 1.25, acetamiprid 1.39, JS598 1.94 and JS599 2.02). We concluded that esterase and glutathione S-transferase play little role in imidacloprid detoxification. The increase of the P450-monooxygenases detoxification is an important mechanism for imidacloprid resistance and target resistance may also exist in this species.

Animals↗
PubMed2004

Metabolism of imidacloprid in Apis mellifera.

Biotransformation of imidacloprid and the appearance of olefin and 5-hydroxyimidacloprid metabolites in the honeybee were studied by HPLC-MS/MS analysis. Honeybees were treated orally with imidacloprid at 20 and 50 microg kg(-1) bee. Imidacloprid was metabolised relatively quickly and thoroughly. Twenty minutes after the beginning of imidacloprid ingestion, the sum of the residues from the three compounds amounted to only 70% of the actual given dose. Imidacloprid, 5-hydroxyimidacloprid and olefin represented, respectively, 50%, 9% and 8% of the actual ingested dose. Six and 24 h, respectively, after ingestion of imidacloprid at 20 and 50 microg kg(-1) bee, imidacloprid could no longer be detected in the honeybee. Imidacloprid had a half-life ranging between 4.5 and 5 h and was rapidly metabolised into 5-hydroxyimidacloprid and olefin. Except 5-hydroxyimidacloprid in the 20 microg kg(-1) treatment, these two metabolites presented a peak value 4 h after ingestion of the 20 and 50 microg kg(-1) doses. This time fully coincided with the appearance of mortality induced by imidacloprid after acute oral intoxication. These results suggested that the immediate neurotoxicity symptoms are due to the action of imidacloprid, whereas 5-hydroxyimidacloprid and/or olefin are involved in honeybee mortality. In addition, it was likely that the 30% of residues undetected 20 min after intoxication were imidacloprid metabolites, although not 5-hydroxyimidacloprid or olefin. Thus, 5-hydroxyimidacloprid and olefin could not be the major metabolites in the worker bees.

Alkenes↗
PubMed2004

Decision making in controlling virus yellows of sugar beet in the UK.

Virus yellows is an important disease affecting yield in sugar beet in the UK. Myzus persicae (Sulzer) is the most effective and efficient aphid vector of the three viruses causing the disease: beet yellows virus, beet mild yellowing virus and beet chlorosis virus. Control of virus yellows disease is thus focused on the study and control of this aphid species. UK national surveys of virus yellows began in 1946 and these data helped to formulate disease forecasting schemes to optimise control. Over the years, in addition to improvements in farm hygiene, periodic changes and developments in control of the disease have occurred. To accommodate these important developments, virus yellows forecasting schemes have evolved accordingly. The most recent version has been adapted to take account of the current widespread use of imidacloprid seed treatment. Its application offers potential to optimise the rational use of aphicides such as imidacloprid so as to benefit beet growers and the environment by reducing prophylactic use of seed treatment.

Animals↗