Is there a risk to honeybees from use of thiamethoxam as a sugar beet seed treatment?

The ban imposed by the European Union on the use of neonicotinoids as sugar beet seed treatments was based on the exposure of bees to residues of neonicotinoids in pollen and nectar of succeeding crops. To address this concern, residues of thiamethoxam (TMX) and clothianidin (CTD) were analyzed in soil collected from fields planted in at least the previous year with thiamethoxam-treated sugar beet seed. This soil monitoring program was conducted at 94 sites across Germany in two separate years. In addition, a succeeding crop study assessed residues in soil, guttation fluid, pollen, and nectar sampled from untreated succeeding crops planted in the season after thiamethoxam seed-treated sugar beet at eight field sites across five countries. The overall mean residues observed in soil monitoring were 8.0 ± 0.5 µg TMX + CTD/kg in the season after the use of treated sugar beet seed. Residue values decreased with increasing time interval between the latest thiamethoxam or clothianidin application before sugar beet drilling and with lower application frequency. Residues were detected in guttation fluid (2.0-37.7 µg TMX/L); however, the risk to pollinators from this route of exposure is likely to be low, based on the reported levels of consumption. Residues of thiamethoxam and clothianidin in pollen and nectar sampled from the succeeding crops were detected at or below the limit of quantification (0.5-1 µg a.i./kg) in 86.7% of pollen and 98.6% of nectar samples and, unlike guttation fluid residues, were not correlated with measured soil residues. Residues in pollen and nectar are lower than reported sublethal adverse effect concentrations in studies with honeybee and bumble bee individuals and colonies fed only thiamethoxam-treated sucrose, and are lower than those reported to result in no effects in honeybees, bumble bees, and solitary bees foraging on seed-treated crops. Integr Environ Assess Manag 2022;18:709-721. © 2021 SYNGENTA. Integrated Environmental Assessment and Management published by Wiley Periodicals LLC on behalf of Society of Environmental Toxicology & Chemistry (SETAC).

Industrial prune processing and its effect on pesticide residue concentrations.

The aim of this study was to determine the insecticide residue processing factor (PF) from plums to prunes and the effect of the industrial processing of prunes residue concentrations. Our results show an increase of insecticide concentrations during plum dehydration that is explained by fruit water loss; however, the normalized insecticide residue concentration, based on plum dry weights to compensate dehydration, was reduced. The water washing and tenderizing of prunes produced insecticide residue reductions of 22.9 ±â€¯4.5% and 21.9 ±â€¯4.2%, respectively. PF were: 1.157, 1.872, 1.316, 0.192, 2.198, 0.775 and 0.156 for buprofezin, l-cyhalothrin, spirodiclofen, indoxacarb, acetamiprid, imidacloprid and emamectin benzoate, respectively, being directly related to water solubility, aqueous hydrolysis and degradation point and inversely related to molecular mass and melting point. In plums for the dehydrated agroindustry the final product is prunes, therefore, it is crucial to consider the PF to determine the specific preharvest interval for this important agroindustry.

Concentrations of imidacloprid and thiamethoxam in pollen, nectar and leaves from seed-dressed cotton crops and their potential risk to honeybees (Apis mellifera L.).

Neonicotinoid insecticides (NIs) have recently been recognized as co-factors in the decline of honeybee colonies because most neonicotinoids are systemic and can transfer into the pollen and nectar of many pollinated crops. In this study, we collected pollen, nectar and leaves from a cotton crop treated with imidacloprid and thiamethoxam to measure the residue levels of these two NIs at different application doses during the flowering period. Then, the residual data were used to assess the risk posed by the systemic insecticides to honeybees following mandated methods published by the European Food Safety Authority (EFSA), and a highly toxic risk to honeybees was highlighted. Imidacloprid was found in both pollen and nectar samples, whereas thiamethoxam was found in 90% of pollen samples and over 60% of nectar samples. Analysis of the pollen and nectar revealed residual amounts of imidacloprid ranging from 1.61 to 64.58 ng g-1 in the pollen and from not detected (ND) to 1.769 ng g-1 in the nectar. By comparison, the thiamethoxam concentrations in pollen and nectar ranged from ND to 14.521 ng g-1 and from ND to 4.285 ng g-1, respectively. The results of this study provide information on the transfer of two NIs from seed treatment to areas of the plant and provides an understanding of the potential exposure of the bee and other pollinators to systemic insecticides.

Identification of Antipneumococcal Molecules Effective Against Different Streptococcus pneumoniae Serotypes Using a Resazurin-Based High-Throughput Screen.

Streptococcus pneumoniae is a major human pathogen, causing around 1.6 million deaths worldwide each year. By optimizing a resazurin-based assay to detect S. pneumoniae growth in 384-well microplates, we developed a new high-throughput screening (HTS) system for the discovery of antipneumococcal molecules, which was unsuccessful using conventional absorbance measurements. Before applying our protocol to a large-scale screen, we validated the system through a pilot screen targeting about 7,800 bioactive molecules using three different S. pneumoniae serotypes. Primary screenings of a further 27,000 synthetic small molecules facilitated the identification of 3-acyl-2-phenylamino-1,4-dihydropquinolin-4-one (APDQ) derivatives that inhibited growth of S. pneumoniae with MIC90 values <1 µM (0.03-0.81 µM). Five selected APDQ derivatives were also active against Staphylococcus aureus but neither Klebsiella pneumoniae nor Pseudomonas aeruginosa, suggesting that APDQ may act specifically against Gram-positive bacteria. Our results both validated and demonstrated the utility of the resazurin-based HTS system for the identification of new antipneumococcal molecules. Moreover, the identified new antipneumococcal molecules in this study may have potential to be further developed as new antibiotics.

Ornamental plants on sale to the public are a significant source of pesticide residues with implications for the health of pollinating insects.

Garden centres frequently market nectar- and pollen-rich ornamental plants as "pollinator-friendly", however these plants are often treated with pesticides during their production. There is little information on the nature of pesticide residues present at the point of purchase and whether these plants may actually pose a threat to, rather than benefit, the health of pollinating insects. Using mass spectrometry analyses, this study screened leaves from 29 different 'bee-friendly' plants for 8 insecticides and 16 fungicides commonly used in ornamental production. Only two plants (a Narcissus and a Salvia variety) did not contain any pesticide and 23 plants contained more than one pesticide, with some species containing mixtures of 7 (Ageratum houstonianum) and 10 (Erica carnea) different agrochemicals. Neonicotinoid insecticides were detected in more than 70% of the analysed plants, and chlorpyrifos and pyrethroid insecticides were found in 10% and 7% of plants respectively. Boscalid, spiroxamine and DMI-fungicides were detected in 40% of plants. Pollen samples collected from 18 different plants contained a total of 13 different pesticides. Systemic compounds were detected in pollen samples at similar concentrations to those in leaves. However, some contact (chlorpyrifos) and localised penetrant pesticides (iprodione, pyroclastrobin and prochloraz) were also detected in pollen, likely arising from direct contamination during spraying. The neonicotinoids thiamethoxam, clothianidin and imidacloprid and the organophosphate chlorpyrifos were present in pollen at concentrations between 6.9 and 81 ng/g and at levels that overlap with those known to cause harm to bees. The net effect on pollinators of buying plants that are a rich source of forage for them but simultaneously risk exposing them to a cocktail of pesticides is not clear. Gardeners who wish to gain the benefits without the risks should seek uncontaminated plants by growing their own from seed, plant-swapping or by buying plants from an organic nursery.

Two low complexity ultra-high throughput methods to identify diverse chemically bioactive molecules using Saccharomyces cerevisiae.

The budding yeast S. cerevisiae is widely used as a eukaryotic model organism to elucidate the mechanism of action of low molecular weight compounds. This report describes the development of two high throughput screening methods based on cell viability either by monitoring the reduction of alamarBlue® (resazurin) or by direct optical measurement of cell growth. Both methods can be miniaturized to allow screening of large numbers of samples, and can be performed using S. cerevisiae in 384 and 1536-well format. The alamarBlue® approach achieves Z' values of >0.7 with signal to basal ratios of >6.5, and around 1.1 million low molecular weight compounds were screened, identifying approximately 25,000 primary hits. Dose response curves generated for a subset (1930) using both alamarBlue® and optical density methods showed significant overlap. In genome-wide haploinsufficiency profiling (HIP), 572 of these hits demonstrated a diverse mechanism of action, affecting >25% of all yeast strains.

Review of field and monitoring studies investigating the role of nitro-substituted neonicotinoid insecticides in the reported losses of honey bee colonies (Apis mellifera).

The nitro-substituted neonicotinoid insecticides, which include imidacloprid, thiamethoxam and clothianidin, are widely used to control a range of important agricultural pests both by foliar applications and also as seed dressings and by soil application. Since they exhibit systemic properties, exposure of bees may occur as a result of residues present in the nectar and/or pollen of seed- or soil-treated crop plants and so they have been the subject of much debate about whether they cause adverse effects in pollinating insects under field conditions. Due to these perceived concerns, the use of the three neonicotinoids imidacloprid, clothianidin and thiamethoxam has been temporarily suspended in the European Union for seed treatment, soil application and foliar treatment in crops attractive to bees. Monitoring data from a number of countries are available to assess the presence of neonicotinoid residues in honey bee samples and possible impacts at the colony level and these are reviewed here together with a number of field studies which have looked at the impact of clothiandin on honey bees in relation to specific crop use and in particular with oilseed rape. Currently there is considerable uncertainty with regards to the regulatory testing requirements for field studies. Accordingly, a testing protocol was developed to address any acute and chronic risks from oilseed rape seeds containing a coating with 10 g clothianidin and 2 g beta-cyfluthrin per kg seeds (Elado®) for managed honey bee (Apis mellifera) colonies, commercially bred bumble bee (Bombus terrestris) colonies and red mason bees (Osmia bicornis) as a representative solitary bee species. This is described here together with a summary of the results obtained as an introduction to the study details given in the following papers in this issue.

Leaching of the Neonicotinoids Thiamethoxam and Imidacloprid from Sugar Beet Seed Dressings to Subsurface Tile Drains.

Pesticide transport from seed dressings toward subsurface tile drains is still poorly understood. We monitored the neonicotinoid insecticides imidacloprid and thiamethoxam from sugar beet seed dressings in flow-proportional drainage water samples, together with spray applications of bromide and the herbicide S-metolachlor in spring and the fungicides epoxiconazole and kresoxim-methyl in summer. Event-driven, high first concentration maxima up to 2830 and 1290 ng/L for thiamethoxam and imidacloprid, respectively, were followed by an extended period of tailing and suggested preferential flow. Nevertheless, mass recoveries declined in agreement with the degradation and sorption properties collated in the groundwater ubiquity score, following the order bromide (4.9%), thiamethoxam (1.2%), imidacloprid (0.48%), kresoxim-methyl acid (0.17%), S-metolachlor (0.032%), epoxiconazole (0.013%), and kresoxim-methyl (0.003%), and indicated increased leaching from seed dressings compared to spray applications. Measured concentrations and mass recoveries indicate that subsurface tile drains contribute to surface water contamination with neonicotinoids from seed dressings.

Optimized combination of dilution and refined QuEChERS to overcome matrix effects of six types of tea for determination eight neonicotinoid insecticides by ultra performance liquid chromatography-electrospray tandem mass spectrometry.

Liquid chromatography-electrospray ionization tandem mass spectrometry (LC-ESI-MS/MS) is a primary tool for analysis of low volatility compounds in complex matrices. However, complex matrices, such as different types of tea, complicate analysis through ionization suppression or enhancement. In this study, sample preparation by a refined QuEChERS method combined with a dilution strategy removed almost all matrix effects caused by six types of tea. Tea samples were soaked with water and extracted with acetonitrile, cleaned up with a combination of PVPP (160mg) and GCB (20mg), and dried. Dried extracts were diluted with 20mL acetonitrile/water (15:85, v/v) before analysis by UPLC-MS/MS. The average recoveries of eight neonicotinoid insecticides (dinotefuran, nitenpyram, thiamethoxam, imidacloprid, clothianidin, imidaclothiz, acetamiprid, and thiacloprid) ranged from 66.3 to 108.0% from tea samples spiked at 0.01-0.5mgkg(-1). Relative standard deviations were below 16% for all recovery tests. The limit of quantification ranged from 0.01 to 0.05mgkg(-1).

[Determination of chlorfenapyr and indoxacarb in tea by gas chromatography-mass spectrometry with solid phase extraction].

OBJECTIVE: To establish a method for simultaneous determination of chlorfenapyr and indoxacarb in tea by gas chromatography-mass spectrometry. METHODS: The tea samples were homogenized and extracted with acetonitrile. Extracts obtained through centrifugation were cleaned up by CARB / NH2 cartridges, and further purified with SLH cartridges. After separated by DB-5MS capillary column( 30 m × 0. 25 mm × 0. 25µm), the analytes were measured by gas chromatography-mass spectrometry in selective ion monitoring( SIM) mode and quantified by external standard method. RESULTS: The linear range was 0. 10- 10 µg / m L for both of the two pesticides. The detection limits of chlorfenapyr and indoxacarb in tea samples were 0. 01 and 0. 008 mg / kg, and the quantitation limits were 0. 03 and 0. 025 mg / kg, respectively. The recoveries were from75. 6% to 92. 7%, and the relative standarddeviations( RSDs) were 3. 6%- 11. 4%( n =6). CONCLUSION: The proposed method has good purification effect and high accuracy, which is capable for simultaneously detecting the chlorfenapyr and indoxacarb in tea samples.

Residues of neonicotinoids and their metabolites in honey and pollen from sunflower and maize seed dressing crops.

A study was carried out to evaluate the possible presence of thiamethoxam, clothianidin and imidacloprid, as well as the metabolic breakdown products of these three neonicotinoids in pollen and honey obtained from brood chamber combs of honeybee colonies located next to sunflower and maize crops from coated seeds. Samples were analyzed by liquid chromatography coupled to quadrupole-time-of-flight mass spectrometry detector, in combination with accurate mass tools such as diagnostic ions by exact mass, chlorine mass filters, and MS/MS experiments. The presence of thiamethoxam and clothianidin was confirmed in some of the pollen samples analyzed. Moreover, different metabolites of neonicotinoids were tentatively detected in the pollen and honey samples collected. The results suggested that four metabolites were found in the honey samples, while for pollen samples eleven metabolites were identified; among these, five were considered for the first time as metabolic breakdown products in sunflower and maize plants.

Field-scale examination of neonicotinoid insecticide persistence in soil as a result of seed treatment use in commercial maize (corn) fields in southwestern Ontario.

Neonicotinoid insecticides, especially as seed treatments, have raised concerns about environmental loading and impacts on pollinators, biodiversity, and ecosystems. The authors measured concentrations of neonicotinoid residues in the top 5 cm of soil before planting of maize (corn) in 18 commercial fields with a history of neonicotinoid seed treatment use in southwestern Ontario in 2013 and 2014 using liquid chromatography-tandem mass spectrometry with electrospray ionization. A simple calculator based on first-order kinetics, incorporating crop rotation, planting date, and seed treatment history from the subject fields, was used to estimate dissipation rate from the seed zone. The estimated half-life (the time taken for 50% of the insecticide to have dissipated by all mechanisms) based on 8 yr of crop history was 0.64 (range, 0.25-1.59) yr and 0.57 (range, 0.24-2.12) yr for 2013 and 2014, respectively. In fields where neonicotinoid residues were measured in both years, the estimated mean half-life between 2013 and 2014 was 0.4 (range, 0.27-0.6) yr. If clothianidin and thiamethoxam were used annually as a seed treatment in a typical crop rotation of maize, soybean, and winter wheat over several years, residues would plateau rather than continue to accumulate. Residues of neonicotinoid insecticides after 3 yr to 4 yr of repeated annual use tend to plateau to a mean concentration of less than 6 ng/g in agricultural soils in southwestern Ontario.

Concentrations of neonicotinoid insecticides in honey, pollen and honey bees (Apis mellifera L.) in central Saskatchewan, Canada.

Neonicotinoid insecticides (NIs) and their transformation products were detected in honey, pollen and honey bees, (Apis mellifera) from hives located within 30 km of the City of Saskatoon, Saskatchewan, Canada. Clothianidin and thiamethoxam were the most frequently detected NIs, found in 68 and 75% of honey samples at mean concentrations of 8.2 and 17.2 ng g(-1) wet mass, (wm), respectively. Clothianidin was also found in >50% of samples of bees and pollen. Concentrations of clothianidin in bees exceed the LD50 in 2 of 28 samples, while for other NIs concentrations were typically 10-100-fold less than the oral LD50. Imidaclorpid was detected in ∼30% of samples of honey, but only 5% of pollen and concentrations were

Neonicotinoid insecticide residues in soil dust and associated parent soil in fields with a history of seed treatment use on crops in southwestern Ontario.

Using neonicotinoid insecticides as seed treatments is a common practice in field crop production. Exposure of nontarget organisms to neonicotinoids present in various environmental matrices is debated. In the present study, concentrations of neonicotinoid residues were measured in the top 5 cm of soil and overlying soil surface dust before planting in 25 commercial fields with a history of neonicotinoid seed treatment use in southwestern Ontario in 2013 and 2014 using liquid chromatography-electrospray ionization tandem mass spectrometry. The mean total concentrations were 3.05 ng/g and 47.84 ng/g in 2013 and 5.59 ng/g and 71.17 ng/g in 2014 for parent soil and soil surface dust, respectively. When surface and parent soil residues were compared the mean concentration in surface dust was 15.6-fold and 12.7-fold higher than that in parent soil in 2013 and 2014, respectively. Pooled over years, the surface dust to parent soil ratio was 13.7, with mean concentrations of 4.36 ng/g and 59.86 ng/g for parent soil and surface dust, respectively. The present study's results will contribute important knowledge about the role these residues may play in the overall risk assessment currently under way for the source, transport, and impact of neonicotinoid insecticide residues in a maize ecosystem.

Sensitive determination of mixtures of neonicotinoid and fungicide residues in pollen and single bumblebees using a scaled down QuEChERS method for exposure assessment.

To accurately estimate exposure of bees to pesticides, analytical methods are needed to enable quantification of nanogram/gram (ng/g) levels of contaminants in small samples of pollen or the individual insects. A modified QuEChERS extraction method coupled with ultra-high-performance liquid chromatography tandem mass spectrometry (UHPLC-MS/MS) analysis was tested to quantify residues of 19 commonly used neonicotinoids and fungicides and the synergist, piperonyl butoxide, in 100 mg samples of pollen and in samples of individual bumblebees (Bombus terrestris). Final recoveries ranged from 71 to 102 % for most compounds with a repeatability of below 20 % for both pollen and bumblebee extracts spiked at 5 and 40 ng/g. The method enables the detection of all compounds at sub-ng/g levels in both matrices and the method detection limits (MDL) ranged from 0.01 to 0.84 ng/g in pollen and 0.01 to 0.96 ng/g in individual bumblebees. Using this method, mixtures of neonicotinoids (thiamethoxam, clothianidin, imidacloprid and thiacloprid) and fungicides (carbendazim, spiroxamine, boscalid, tebuconazole, prochloraz, metconazole, fluoxastrobin, pyraclostrobin and trifloxystrobin) were detected in pollens of field bean, strawberry and raspberry at concentrations ranging from MDL, and in some bees, the fungicides carbendazim, boscalid, tebuconazole, flusilazole and metconazole were present at concentrations between 0.80 to 30 ng/g. This new method allows the analysis of mixtures of neonicotinoids and fungicides at trace levels in small quantities of pollen and individual bumblebees and thus will facilitate exposure assessment studies.

Bees prefer foods containing neonicotinoid pesticides.

The impact of neonicotinoid insecticides on insect pollinators is highly controversial. Sublethal concentrations alter the behaviour of social bees and reduce survival of entire colonies. However, critics argue that the reported negative effects only arise from neonicotinoid concentrations that are greater than those found in the nectar and pollen of pesticide-treated plants. Furthermore, it has been suggested that bees could choose to forage on other available flowers and hence avoid or dilute exposure. Here, using a two-choice feeding assay, we show that the honeybee, Apis mellifera, and the buff-tailed bumblebee, Bombus terrestris, do not avoid nectar-relevant concentrations of three of the most commonly used neonicotinoids, imidacloprid (IMD), thiamethoxam (TMX), and clothianidin (CLO), in food. Moreover, bees of both species prefer to eat more of sucrose solutions laced with IMD or TMX than sucrose alone. Stimulation with IMD, TMX and CLO neither elicited spiking responses from gustatory neurons in the bees' mouthparts, nor inhibited the responses of sucrose-sensitive neurons. Our data indicate that bees cannot taste neonicotinoids and are not repelled by them. Instead, bees preferred solutions containing IMD or TMX, even though the consumption of these pesticides caused them to eat less food overall. This work shows that bees cannot control their exposure to neonicotinoids in food and implies that treating flowering crops with IMD and TMX presents a sizeable hazard to foraging bees.

Dynamic behaviour and residual pattern of thiamethoxam and its metabolite clothianidin in Swiss chard using liquid chromatography-tandem mass spectrometry.

A simultaneous method was developed to analyse thiamethoxam and its metabolite clothianidin in Swiss chard using tandem mass spectrometry (in the positive electrospray ionisation mode using multiple reaction monitoring mode) to estimate the dissipation pattern and the pre-harvest residue limit (PHRL). Thiamethoxam (10%, WG) was sprayed on Swiss chard grown in two different areas under greenhouse conditions at the recommended dose rate of 10 g/20 L water. Samples were collected randomly up to 14 days post-application, extracted using quick, easy, cheap, effective, rugged, safe (QuEChERS) acetate-buffered method and purified via a dispersive solid phase extraction (d-SPE) procedure. Matrix matched calibration showed good linearity with determination coefficients (R(2)) ⩾ 0.998. The limits of detection (LOD) and quantification (LOQ) were 0.007 and 0.02 mg/kg. The method was validated in triplicate at two different spiked concentration levels. Good recoveries (n=3) of 87.48-105.61% with relative standard deviations (RSDs) < 10 were obtained for both analytes. The rate of disappearance of total thiamethoxam residues in/on Swiss chard was best described by first-order kinetics with half-lives of 6.3 and 4.2 days. We predicted from the PHRL curves that if the residues were <19.21 or 26.98 mg/kg at 10 days before harvest, then total thiamethoxam concentrations would be below the maximum residue limits during harvest.

Potential exposure of pollinators to neonicotinoid insecticides from the use of insecticide seed treatments in the mid-southern United States.

Research was done during 2012 to evaluate the potential exposure of pollinators to neonicotinoid insecticides used as seed treatments on corn, cotton, and soybean. Samples were collected from small plot evaluations of seed treatments and from commercial fields in agricultural production areas in Arkansas, Mississippi, and Tennessee. In total, 560 samples were analyzed for concentrations of clothianidin, imidacloprid, thiamethoxam, and their metabolites. These included pollen from corn and cotton, nectar from cotton, flowers from soybean, honey bees, Apis mellifera L., and pollen carried by foragers returning to hives, preplanting and in-season soil samples, and wild flowers adjacent to recently planted fields. Neonicotinoid insecticides were detected at a level of 1 ng/g or above in 23% of wild flower samples around recently planted fields, with an average detection level of about 10 ng/g. We detected neonicotinoid insecticides in the soil of production fields prior to planting at an average concentration of about 10 ng/g, and over 80% of the samples having some insecticide present. Only 5% of foraging honey bees tested positive for the presence of neonicotinoid insecticides, and there was only one trace detection (< 1 ng/g) in pollen being carried by those bees. Soybean flowers, cotton pollen, and cotton nectar contained little or no neonicotinoids resulting from insecticide seed treatments. Average levels of neonicotinoid insecticides in corn pollen ranged from less than 1 to 6 ng/g. The highest neonicotinoid concentrations were found in soil collected during early flowering from insecticide seed treatment trials. However, these levels were generally not well correlated with neonicotinoid concentrations in flowers, pollen, or nectar. Concentrations in flowering structures were well below defined levels of concern thought to cause acute mortality in honey bees. The potential implications of our findings are discussed.

Residue and dissipation kinetics of thiamethoxam in a vegetable-field ecosystem using QuEChERS methodology combined with HPLC-DAD.

The dissipation kinetics and residual levels of thiamethoxam in potato and soil under field ecosystem were determined using a QuEChERS method with HPLC-DAD. At fortification levels of 0.05, 0.1, 0.25, 0.5, 1.0 and 5.0 mg kg(-1), it was shown recovery was 99.4% (95.3-103.5%) for potato tubers, and 88.5% (86-91%) for soil with coefficient variation of the method (CV%) was less than 4% in potato tubers, and in soil less than 11%. For repeatability ranged from 1.27% to 4.77%. The LOD and LOQ were estimated to be 0.02 and 0.06 mg kg(-1), respectively. The half-lives were 2.92 and 1.4 days, respectively. The terminal residues of thiamethoxam were below the maximum residue limit (MRL 0.2 mg kg(-1)) after 6 days, which considered to be safe for human beings. These results contribute to establishing the scientific basis of the dosage of thiamethoxam for use in vegetable-field ecosystems.

Variable concentration of soil-applied insecticides in potato over time: implications for management of Leptinotarsa decemlineata.

BACKGROUND: Select populations of Colorado potato beetle, Leptinotarsa decemlineata, in Wisconsin have recently become resistant to soil-applied neonicotinoids in potato. Sublethal insecticide concentrations persisting in foliage through the growing season may select for resistance over successive years of use. Over the 2 years of this study, the aim was to document the in-plant insecticide concentrations over time that result from four different types of soil-applied insecticide delivery for thiamethoxam and imidacloprid in potato, and to measure the impact upon L. decemlineata populations following treatments. After plant emergence, insect life stages were counted and plant tissue was assayed weekly for nine consecutive weeks using ELISA. RESULTS: Peak concentration of both imidacloprid and thiamethoxam occurred in the first sample week following plant emergence. The average concentration of both insecticides dissipated sharply over time as the plant canopy expanded 50 days after planting in all delivery treatments. Both insecticides were detected at low levels during the later weeks of the study. Among-plant concentrations of both neonicotinoids were highly variable throughout the season. Populations of L. decemlineata continued to develop and reproduce throughout the period of declining insecticide concentrations. CONCLUSION: Sublethal, chronic exposure to soil-applied systemic insecticides resulting from these delivery methods may accelerate selection for resistant insects in potato.