Residues of synthetic pyrethroid insecticides on horticultural crops

Foliar applications of synthetic pyrethroids were made to several crops to determine residue levels at various intervals after application. On onions, residues of cypermethrin, permethrin and fenvalerate were negligible > 0.1 mg kg^?1, 7 days after application. On lettuce, residues of fenvalerate and permethrin were 0.8 mg kg^?1. On celery, residues of fenvalerate did not decline and ranged from 0.12 to 0.25 mg kg^?1 during the 14-day period. On green bush-beans, residues of permethrin and cypermethrin did not decline during the 14-day period and ranged from 0.1 to 0.6 mg kg^?1. By day 7, residues of cyfluthrin, cypermethrin, deltamethrin, fenvalerate and permethrin on strawberries were less than the acceptable maximum tolerance of 0.1 mg kg^?1 with the exception of cypermethrin, applied at the rate of 0.14 kg a.i. ha^?1 which gave a residue of 0.14 mg kg^?1.     

Permethrin and deltamethrin residues on lettuce

Permethrin and deltamethrin, two synthetic pyrethroid insecticides, are registered in several countries for use on lettuce. Both chemicals were applied on autumn and spring grown lettuce in the glasshouse. When applied at the normal prescribed dose rates of 25 and 12.5 g a.i. ha^?1, < 1 mg kg^?1 of either compound was found in the lettuce at harvest, even when applied only a few days before harvest. The total amount of active ingredient applied was too low to reach the 1 mg kg^?1 level when evenly applied on marketable lettuce heads weighing about 200 g each. Applying a higher dose than 25 g permethrin a.i. ha^?1 or 12.5 g deltamethrin a.i. ha^?1, or applying two applications in the 2 weeks prior to harvest, may well result in residue levels higher than the maximum residue limit of 1 mg kg^?1 for permethrin and certainly higher than the maximum residue limit of 0.2 mg kg^?1 for deltamethrin, which is more persistent.     

Organophosphorothioates and synergised synthetic pyrethroids as grain protectants on bulk wheat

Organophosphorothioates and synergised synthetic pyrethroids were used in duplicate field trials carried out on bulk wheat in commercial silos in Queensland and New South Wales. Laboratory bioassays using malathion-resistant strains of insects were carried out on samples of treated grain at intervals over 9 months. These established that all treatments were generally effective. Deltamethrin (2 mg kg^?1)+ piperonyl butoxide (8 mg kg^?1), fenitrothion (12 mg kg^?1)+ fenvalerate (1 mg kg^?1)+ piperonyl butoxide (8 mg kg^?1), fenitrothion (12 mg kg^?1)+ phenothrin (2 mg kg^?1)+ piperonyl butoxide (8 mg kg^?1) and pirimiphos-methyl (4 mg kg^?1)+ permethrin (1 mg kg^?1)+ piperonyl butoxide (8 mg kg^?1) controlled common field strains of Sitophilus oryzae (L.) and Rhyzopertha dominica (F.). Against a highly resistant strain of S. oryzae, deltamethrin (2 mg kg^?1)+ piperonyl butoxide (8 mg kg^?1) was superior to the remaining treatments. All treatment combinations completely prevented progeny production in Tribolium castaneum (Herbst), T. confusum Jacquelin du Val and in Ephestia cautella (Walker). Residues of deltamethrin, fenvalerate, permethrin and phenothrin were determined and shown to be highly persistent on stored wheat. During milling, residues accumulated in the bran fractions and were reduced in white flour. They were not significantly reduced during baking.     

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.     

Behaviour of trifloxystrobin and tebuconazole on grapes under semi‐arid tropical climatic conditions

BACKGROUND: A mixture of trifloxystrobin and tebuconazole is excellent in controlling both powdery and downy mildew of grapes. The objective of the present work was to study the behaviour of trifloxystrobin and tebuconazole on grape berries and soil following treatment with Nativo 75 WG, a formulation containing both fungicides (trifloxystrobin 250 + tebuconazole 500 g kg^?1). This study was carried out for planned registration of this mixture for use on grapes in India. RESULTS: Initial residue deposits of trifloxystrobin and tebuconazole on grapes were below their maximum residue limit (MRL) of 0.5 and 2 mg kg^?1, respectively, when Nativo 75 WG was applied at the recommended dose of 175 g product ha^?1. The residues dissipated gradually to 0.02 and 0.05 mg kg^?1 by 30 days, and were below the quantifiable limit of 0.01 mg kg^?1 at the time of harvest (60 days after the last treatment). Trifloxystrobin and tebuconazole dissipated at a pre‐harvest interval (PHI) of 36 and 34 days, respectively, from the recommended treatment dose. The acid metabolite of trifloxystrobin, CGA 321 113, was not detected in grape berries at any point in time. Soil at harvest was free of any pesticide residues. CONCLUSION: Residue levels of both trifloxystrobin and tebuconazole were below MRLs when grapes were harvested 30 days after the last of four applications of 175 g product ha^?1 (trifloxystrobin 44 g AI ha^?1, tebuconazole 88 g AI ha^?1) under the semi‐arid tropical climatic conditions of India. 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.     

Residue levels of three organophosphorus insecticides in sweet pepper grown in commercial greenhouses

The degradation rates and residue levels of diazinon, pirimiphos-methyl and chlorpyrifos in the leaves and fruits of pepper plants grown in commercial greenhouses were studied using g.l.c. Analysis of leaves at intervals following application showed that the initial residue of diazinon was higher than that of the other two insecticides, while its dissipation rate was faster. The dissipation of chlorpyrifos in fruits was faster than diazinon. The maximum residue levels (m.r.l.) of diazinon (0.5 mg kg^?;1) and chlorpyrifos (0.1 mg kg^?;1) were reached after 13 and 8 days of application respectively. With diazinon and pirimiphos-methyl, sprayed 3 weeks before inflorescence, very low concentrations of both insecticides were found in fruits, although these compounds have no systemic behaviour. Chlorpyrifos residue level of 0-2 mg kg ^?;1 in harvested fruits did not drop below m.r.l. after 11 days holding period.     

Toxico‐kinetics,recovery efficiency and microsomal changes following administration of deltamethrin to black Bengal goats

A study of the toxico‐kinetics, recovery percentage from different substrates, cytotoxicity and role of cytochrome P₄₅₀ and b₅ of liver microsome in the metabolism of deltamethrin were carried out in female black Bengal goat. The ALD₅₀ value of deltamethrin in goat by intravenous route lies between 0.2 and 0.6 mg kg^?1. Intravenous disposition kinetics using a dose of 0.2 mg kg^?1 showed that the maximum blood concentration of deltamethrin was recorded at 0.5 min, followed by rapid decline, and a minimum concentration was detected at 6 min after administration. The following values were obtained : Vd_area 0.148 (± 0.02) litre kg^?1; t_1/2 (α) 0.22 (± 0.02) min; t_1/2 (β) 2.17 (± 0.37) min; K_el 1.05 (± 0.24) min^?1; AUC 4.30(± 0.45) µg min ml^?1; Cl_B 0.05 (± 0.006) litre kg^?1 min^?1; T～B 1.93 (± 0.58); fc 0.40(± 0.05). After 10 min, liver retained the maximum residue, and heart, adrenal gland, kidney, spleen, fat and brain also held the insecticide; liver, fat, heart and spleen retained residue after 30 min, and bone, liver and fat retained residue after 60 min of intravenous administration. Oral absorption of deltamethrin was poor and inconsistent, and approximately 65% of administered dose was recovered from faeces and gastrointestinal contents. The excretion of deltamethrin through urine was meagre, and only 0.01 and 0.013% of the administered dose was recovered after 3 and 5 days of oral administration respectively. All the tissues retained the residue after 3 days; while fat, rumen, reticulum, omasum, abomasum, large and small intestine and bone retained the residue after 5 days of oral administration; and the percentage recoveries were 1.73 and 0.027 respectively. Deltamethrin reduced the level of cytochrome P₄₅₀ content of liver microsomal pellet of goat after 5 days of oral administration. Histopathological examination of liver, kidney, heart, spleen brain and lung sections of treated goats did not reveal any pathological changes. © 2001 Society of Chemical Industry     

Dissipation rates of insecticides in six minor vegetable crops grown on organic soils in Ontario,Canada

Dissipation rates of diazinon, endosulfan, leptophos, methamidophos, methomyl, parathion and pirimicarb were studied on five minor vegetable crops, including cos and head lettuce, endive, cauliflower and Chinese cabbage. Residues from foliar treatment generally followed an exponential rate of decline. The number of days for residues to drop to below acceptable tolerances was highly dependent on the magnitude of the initial residue; large variations in initial residues were observed between years, between insecticides, and between crop types. Residues of five insecticides and two fungicides used in furrow treatments for onions intended for pickling were determined in the onions at harvest and after pickling. Fensulfothion and fonofos levels were below the accepted tolerance of 0.1 mg kg^?1 at harvest, while chlorfenvinphos, chlorpyrifos and ethion were present above this level; fungicide residues were not detected. Following pickling, only ethion residues were still present in the onions at levels greater than 0.1 mg kg^?1.     

Pyrethroid insecticide residues on vegetable crops

Pyrethroid insecticides were applied on various vegetable crops as foliar treatments to determine dissipation rates. On Chinese broccoli (Guy Lon), Chinese mustard (Pak Choi) and Chinese cabbage (Kasumi, napa), fenvalerate was persistent with residues of 0.10, 0.14 and 0.11 mg kg-1, respectively, by day 21. Cypermethrin residues on head lettuce were below 0.1 mg kg-1 by day 10 but on the leafier romaine and endive varieties it was more persistent and required 14-19 days to dissipate below this concentration. After three applications, residues of cypermethrin in harvested carrots and of permethrin in eggplant were not detected on the day of application. On asparagus, deltamethrin and cypermethrin residues declined to less than 0.1 mg kg-1 by days 1 and 2, respectively; permethrin was more persistent, requiring more than 2 days to decline to less than 0.1 mg kg-1. Deltamethrin on dry (cooking) and Spanish onions was not detected on the day of application. On tomatoes, the concentration of permethrin was 0.093 mg kg-1 on the day of application and declined to about 0.05 mg kg-1 after 2-4 days. In general, permethrin, cypermethrin and deltamethrin residues declined to acceptable concentrations within an acceptable pre-harvest interval. Fenvalerate may be too persistent on these speciality crops unless a maximum residue limit > 0.1 mg kg-1 is permitted.     

Protective action of fenvalerate,deltamethrin, and four stereoisomers of permethrin against black flies (Simulium spp.) attacking cattle

Fenvalerate, deltamethrin, (1R)-cis-permethrin, (1R)-trans-permethrin and (1S)-trans-permethrin, applied topically to the entire body surface of steers at a rate of 1 mg a.i. kg⁻¹, provided 70% or better protection from black flies on cattle for 16, 9, 8, 6 and 6 days, respectively. The (1S)-cis stereoisomer of permethrin was ineffective as a protectant against black flies at a rate of 1 mg a.i. kg⁻¹ when applied as a total body spray. One poly(vinyl chloride) ear tag containing 10% permethrin, in each ear of steers, provided protection from black fly attack for up to 13 days under field conditions. Poly(vinyl chloride) ear tags containing 8% fenvalerate, installed in each ear of steers, did not provide satisfactory protection from black flies under field conditions.     

Synthetic pyrethroids: Toxicity and synergism on dietary exposure of Tribolium castaneum (Herbst) larvae

The potency of six dietary pyrethroids, as toxicants and inhibitors of weight gain in first- and fourth-instar Tribolium castaneum (Herbst) larvae, decreased in the order of cis-cypermethrin and deltamethrin > trans-cypermethrin and cis-permethrin > fenvalerate and trans-permethrin. Dosages that reduced larval weight also delayed pupation and emergence, probably due to their antifeeding activity. Three oxidase inhibitors (piperonyl butoxide, O, O-diethyl O-phenyl phosphorothioate, and O-isobutyl O-prop-2-ynyl phenylphosphonate), at a dietary concentration of 100 mg kg^?1, had little or no effect on the toxicity of trans-permethrin, but strongly synergised the toxicity of cis-cypermethrin by about 3-, 3- and 10-fold, respectively. Piperonyl butoxide also synergised the toxicity of cis-permethrin, trans-cypermethrin and deltamethrin, but not that of fenvalerate. On the other hand, an esterase inhibitor, profenofos, did not enhance the potency of any of the α-cyano-3-phenoxybenzyl pyrethroids. Oxidases appear to be more important than esterases in pyrethroid detoxification by T. castaneum larvae.     

Influence of block and cell size,growing medium and insecticide dose on the behaviour and uptake of phorate by lettuce and uptake of carbofuran and chlorfenvinphos by calabrese

Phorate residues in peat blocks and lettuce were determined following incorporation of the insecticide into different block and ‘Speedling’ cell sizes. Between-block variability was influenced little by block size. Phorate oxidation was most extensive in the largest blocks containing the smallest dose. Total residue concentrations in the lettuce declined from the time of planting to harvest, although accumulation of insecticide continued and was related more to dose than to block or cell size. Residues in the lettuce at harvest exceeded the proposed maximum limit of 0.2 mg kg^?1 in some treatments. Residues at planting comprised mainly the parent sulphoxide and sulphone, but by harvest, the oxygen analogue sulphoxide and sulphone predominated. Lettuce weight was not influenced by dose but was related directly to block size. Carbofuran and chlorfenvinphos residues were determined in calabrese sown into two sizes of blocks. At planting time, carbofuran residue concentrations were 100 times greater than those of chlorfenvinphos but residues of both insecticides in the mature heads were < 0.01 mg kg^?1. Seedling weights in both sowings declined with increasing concentrations of the insecticides. It was concluded that manipulations of block size and the dose of insecticide need to be evaluated for individual insecticide/crop combinations to exploit the technique fully.     

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 azinphos-methyl usage and residues on grapes and in wine in Australia

Azinphos-methyl was applied to Shiraz winegrapes by commercial high-volume and hand-held sprayers during seasons 1993/94 and 1994/95. Residue levels in grapes resulting from treatments applied by commercial sprayer were below the maximum residue level (MRL) of 2 mg kg^-1 for grapes in Australia, whereas residues resulting from treatments applied by hand-held sprayer still exceeded the MRL five weeks after final application. There was a strong correlation for most treatments between treatment concentration of azinphos-methyl and residue level in grapes, and in wine made from treated grapes. Applied at the recommended rate (1·2 g litre^-1 wettable powder (WP) and 2·4 ml litre^-1 suspension concentrate (SC)) by commercial high-volume sprayer, azinphos-methyl residue levels in wine were well below the MRL, and below the MRLs of most importing countries, except Denmark and Sweden. When applied by hand-held sprayer, residue levels in wine were 5·9–29·6 fold higher than those previously obtained by commercial application of insecticide. Since wines are often blends from different grape blocks and grape-growing districts, in practice, this is unlikely to be of concern. Wine made from grapes treated by commercial sprayer showed no detectable residues of azinphos-methyl after one year of storage. In both years, residue levels in grapes of both formulations of azinphos-methyl fluctuated during the five-week post-treatment period, although there was an overall downward trend. Previously unrecorded systemicity in azinphos-methyl was demonstrated in laboratory studies with barley seedlings, and this may explain these fluctuating data in grapes. The reduction of azinphos-methyl residues in grapes over time appears to be a complex phenomenon involving translocation of active ingredient combined with an increase in the size and weight of berries, producing fluctuating residue levels. © 1998 SCI     

Accumulation of endosulfan residues in fish and their predators after aerial spraying for the control of tsetse fly in Botswana

Residues of endosulfan insecticide (α- and β-isomers, and ‘endosulfan sulphate’) in fish and their predators were measured during and after operations to control tsetse fly in the Okavango Delta, Botswana. Six ultra-low-volume doses of endosulfan 35% e.c. (6–12 g a.i. ha^?1) were applied from the air in a period of 12 weeks over 2500 km². The concentration of residues found in living fish was up to 0.19 mg kg^?1 wet wt in caudal muscle, and usually < 0.8 mg kg^?1 wet wt in pooled viscera (maximum 2.8 mg kg^?1). These values returned to near-normal within 3 months after cessation of spraying, but residues were still detectable after 12 months. By comparison, fish killed by spraying contained a maximum residue level (whole-body) of 1.5 mg kg^?1 wet wt. The residue level in fish was approximately proportional to their fat content. Lean fish were more susceptible to poisoning than fat fish. The proportion of the ‘endosulfan sulphate’ metabolite in fish increased at least six times with respect to the parent isomers (α+β) during the period of spraying, but more advanced stages of metabolic breakdown were not monitored. Residue levels in fish predators (fish-eating birds and crocodiles) were similar to those in their prey, and the risk to them was consequently low.     

Uptake of phorate by lettuce

Following experimental and commercial applications to soil of a granular formulalation of phorate (O,O-diethyl S-ethylthiomethyl phosphorodithioate), residues in the soil and in lettuce were determined by gas-liquid chromatography. When applied by the bow-wave method as a continuous logarithmically-changing dose ranging from approximately 0.9 to 16.0 kg a.i. ha^?1, the proportional rate of oxidation in soil of phorate sulphoxide to phorate sulphone was inversely related to dose. Ten weeks after application, total phorate residues in the soil had declined by about 35% at all dose levels. Residues in mature lettuce, from the 1-5 kg ha^?1 dose-range, comprised the parent and oxygen analogue sulphoxides and sulphones; the relative proportions of the individual metabolites were independent of dose. Over this dose-range, total residue concentrations in the crop became proportionally slightly greater with increasing dose. When single doses of 1.1, 2.0 or 2.2 kg a.i. ha^?1 were applied at drilling, the total residue concentrations in the lettuce declined from 5 mg kg^?1 in seedlings from some treatments to <0.05 mg kg^?1 at harvest. In plants raised in peat blocks containing 10 or 20 mg a.i. per block, however, residues in seedlings totalled 45-47 mg kg^?1 and declined to only 0.7 mg kg^?1 at harvest. It was concluded that bowwave applications of phorate when field-sowing lettuce were unlikely to lead to unacceptable residues in the harvested crop, but that residues in lettuce raised in phorate-treated peat blocks may be unacceptably high.     

The effect of the annual use of pesticides on soil microorganisms,pesticide residues in the soil and barley yields

A study has been made of the influence of pesticides used annually on soil microorganisms and crop yields. The persistence of these pesticides in the soil was also investigated. The herbicides MCPA, glyphosate, maleic hydrazide and tri-allate, and the insecticide parathion, were applied on experimental plots on which barley was grown during the years 1973-1981. The fungicide 2-methoxyethylmercury chloride was used every year for dressing the seeds grown in pesticide-treated plots. The pesticide treatments did not affect significantly the numbers of several groups of soil microorganisms. A slight increase was, however, observed in the nitrification activity in the soil. The barley yields were on average higher on pesticide-treated plots than on controls because of successful weed control. Pesticide residues in the soil were generally very low; for example, for parathion they were below 0.02 mg kg^?1 within 11 days, and for MCPA 0.06 mg kg^?1 within 7 days. However, the glyphosate residue was 1.6 mg kg^?1 in the autumn 2 days after the treatment, and the residue settled to a level of 0.2 mg kg^?1 during the following summer. No clear dependence was observed between the residue level and the time between treatment and sampling.     

Residues of the algicide endothal in water,soil and rice,after paddy field applications

In order to obtain residue data from the application of the algicide endothal in Italian rice paddy fields, two experiments were carried out using a 50 g kg^?1 granular formulation in a small pond and the same granular and two liquid formulations in actual paddy fields of the Italian rice growing area. Endothal decay in the pond water was very rapid, reaching residue levels of 0·01-1·02 mg litre^?1 in two days and 0·004-0·01 mg litre^?1 at the third day. The muddy soil of the pond was free from measurable endothal residues( <0·02 mg kg^?1). In the paddy-field waters, the endothal decay was slower, with an average half-life time of 3·3 days, independently of the type of formulation. The actual residues in water after 6 days ranged from 0·3 to 1·3 mg litre^?1 according to the initial amount of product applied, and, consequently, to the initial concentration in water. Rice samples collected at the normal harvest time from the two paddy fields, treated with three different formulations, showed no endothal residue at the minimum detectable level of 0·01 mg kg^?1.     

Risk posed to honeybees (Apis mellifera L,Hymenoptera) by an imidacloprid seed dressing of sunflowers

In a greenhouse metabolism study, sunflowers were seed‐treated with radiolabelled imidacloprid in a 700 g kg^?1 WS formulation (Gaucho® WS 70) at 0.7 mg AI per seed, and the nature of the resulting residues in nectar and pollen was determined. Only the parent compound and no metabolites were detected in nectar and pollen of these seed‐treated sunflower plants (limit of detection <0.001 mg kg^?1). In standard LD₅₀ laboratory tests, imidacloprid showed high oral toxicity to honeybees (Apis mellifera), with LD₅₀ values between 3.7 and 40.9 ng per bee, corresponding to a lethal food concentration between 0.14 and 1.57 mg kg^?1. The residue level of imidacloprid in nectar and pollen of seed‐treated sunflower plants in the field was negligible. Under field‐growing conditions no residues were detected (limit of detection: 0.0015 mg kg^?1) in either nectar or pollen. There were also no detectable residues in nectar and pollen of sunflowers planted as a succeeding crop in soils which previously had been cropped with imidacloprid seed‐treated plants. Chronic feeding experiments with sunflower honey fortified with 0.002, 0.005, 0.010 and 0.020 mg kg^?1 imidacloprid were conducted to assess potential long‐term adverse effects on honeybee colonies. Testing end‐points in this 39‐day feeding study were mortality, feeding activity, wax/comb production, breeding performance and colony vitality. Even at the highest test concentration, imidacloprid showed no adverse effects on the development of the exposed bee colonies. This no‐adverse‐effect concentration of 0.020 mg kg^?1 compares with a field residue level of less than 0.0015 mg kg^?1 ( = limit of detection in the field residue studies) which clearly shows that a sunflower seed dressing with imidacloprid poses no risk to honeybees. This conclusion is confirmed by observations made in more than 10 field studies and several tunnel tests. © 2001 Society of Chemical Industry