Field Application Rates Research Articles

Potential of flavesone as a grain protectant: Long-term efficacy and residues for controlling the lesser grain borer, Rhyzopertha dominica (F.), in stored wheat

A study was undertaken to evaluate the synthetic biopesticide, flavesone, as a potential grain protectant for the lesser grain borer, Rhyzopertha dominica (F.), in wheat. The search for new grain protectants is critical because of the propensity of R. dominica to develop genetic resistance to various insecticides such as organophosphates (OPs), carbamates, synthetic pyrethroids and juvenile hormone analogues. Wheat was treated with 0, 60, 90 or 120 ppm of flavesone as it passed through an auger into large (1 tonne) storage bags. The treated wheat was stored for 13 months under sheltered ambient conditions in southeast Queensland, and samples were also collected 1 week after treatment and stored for 13 months in the laboratory at 30 °C and 55% RH for comparative purposes. Bioassays of wheat stored under laboratory and ambient conditions, showed that an application rate of 60 ppm provided protection for at least 13 months from a susceptible strain, based on high levels of suppression of the F1 generation. Untreated wheat stored under ambient conditions became heavily infested with R. dominica, while none were detected in any of the treatments, thus further confirming the potential of flavesone as an effective grain protectant. However, bioassays showed that the 60-ppm rate only provided 3 months protection from a strain that was resistant to OPs and pyrethroids, indicating potential non-target site resistance present in this strain. Higher application rates of 90 and 120 ppm were required for 13 months protection. As reported in some other grain protectant studies, initial flavesone residues were lower than the targeted rates, suggesting potential for improving formulation and application methods. Flavesone residues remained relatively stable throughout the study period. We believe that the data generated through this study will provide foundation in establishing field application rate for this new molecule and its possible registration for use by industry to mitigate resistance problems.

Development of an HPPD-Inhibitor Resistant Wheat and Multiomics Integrative Analysis of Herbicide Toxicity and OsHIS1 Detoxification in Wheat.

Weed infestation in agricultural fields significantly diminishes crop yields. Herbicides are widely used as a primary method of weed control. Developing herbicide-resistant crops through the expression of resistant genes represents a sustainable approach. This study generated wheat germplasms highly resistant to 4-hydroxyphenylpyruvate dioxygenase (HPPD)-inhibiting herbicides by transforming the rice HPPD INHIBITOR SENSITIVE 1 (OsHIS1) gene into Xinong 511, conferring resistance to mesotrione at levels up to nine times the typical field application rate (1350 g ai ha-1). Agronomic trait evaluations under greenhouse and field conditions showed no additional effects on wheat. Herbicide susceptibility assays confirmed the specific resistance to different HPPD inhibitors. Transcriptome and metabolome analyses revealed regulation of flavonoid and photosynthesis-antenna protein pathways in the herbicide functional. Collectively, OsHIS1 could be applied in the production of herbicide-resistant wheat.

Simulated herbicide drift alters native plant flowering phenology.

Data for herbicide effects on plant flowering are needed to determine potential impacts on plant reproduction. Thus, flowering phenology was determined for up to 12 weeks after herbicide treatment for native Willamette Valley plants growing in small plots on two Oregon State University experimental farms. Six perennial species were evaluated: Camassia leichtlinii (CALE), Elymus glaucus (ELGL), Eriophyllum lanatum (ERLA), Festuca idahoensis subsp. roemeri (FEID), Iris tenax (IRTE), and Prunella vulgaris var. lanceolata (PRVU). Effects of glyphosate and dicamba, alone and in combination, were determined using simulated drift rates of 0.1 or 0.2 x field application rates (FAR) of 1119 g ha-1 active ingredient (a.i.) (830 g ha-1 acid glyphosate) for glyphosate and 560 g ha-1 a.i. for dicamba. Flowering phenology was evaluated as stage of development on a scale from no buds (converted to 0), buds (1), pre-flowering (2), flowering (3), post-flowering (4), to mature seeds (5) before herbicide treatment and for 12 weeks after treatment. Flowering response to herbicides varied by species and farm; but, in general, dicamba and glyphosate resulted in earlier flowering stages (delayed or not full flowering) for the dicot ERLA, and to a lesser extent, PRVU; and glyphosate resulted in earlier flowering stages for the monocot IRTE. Based on these data, the concentration of herbicide affecting flowering stage was 0.1 x FAR. Once flowering stage was inhibited by dicamba and glyphosate, plants generally did not recover to full flowering. This study provided evidence that common herbicides can affect flowering phenology of native plants with implications for seed production.

Nanobody Mediated Atrazine Resistance in Plants.

In planta expression of recombinant antibodies has been proposed as a strategy for herbicide resistance but is not well advanced yet. Here, an atrazine nanobody gene fused with a green fluorescent protein tag was transformed to Arabidopsis thaliana, which was confirmed with PCR, ELISA, and immunoblotting. High levels of nanobody accumulation were observed in the nucleus, cytoderm, and cytosol. The nanobody expressed in the plant had similar affinity, sensitivity, and selectivity as that expressed in Escherichia coli. The T3 homozygous line showed resistance in a dose-dependent manner up to 380 g ai/ha of atrazine, which is approximately one-third of the recommended field application rate. This is the first report of utilizing a nanobody in plants against herbicides. The results suggest that utilizing a high-affinity herbicide nanobody gene rather than increasing the expression of nanobodies in plants may be a technically viable approach to acquire commercial herbicide-resistant crops and could be a useful tool to study plant physiology.

Seed dormancy, germination requirements, and implications of herbicides for Penstemon albidus and P. nitidus

Seed‐based restoration is dependent on seed germination, and poor germination can cause restoration failure. Many restoration failures can be attributed to a lack of knowledge of germination characteristics, species‐specific seed dormancy, or the effects of widely used herbicides on germination. White penstemon (Penstemon albidus) and Waxleaf penstemon (P. nitidus) are native to the Northern Great Plains region of North America, and increased germination of these species would contribute to improved restoration in the region. We performed two concurrent experiments to determine: (1) the germination requirements and dormancy class of these species; and (2) the effects of herbicides on germination. To determine germination requirements, we applied pretreatments (scarification, smoke, and KNO3) and three durations (2, 4, and 8 weeks) of cold and warm stratification. To test the effects of herbicides on germination, three commonly used herbicides (atrazine, trifluralin, and 2,4‐D) were applied at six concentrations (100, 50, 10, 1, 0.1, and 0% of the recommended field application rate). Germination characteristics indicate both species express physiological dormancy. Physiological dormancy denotes an embryo with low growth potential that is unable to overcome mechanical constraints but can be alleviated with proper temperature cues. Both species required cold stratification, with P. nitidus needing a longer period (8 weeks) than P. albidus (4 weeks). Final germination percentage of P. albidus decreased with higher doses of 2,4‐D but was not affected by atrazine or trifluralin. These experiments help to create protocol for the use of our study species, as well as other species, in restoration plantings.

Cyclobutrifluram (TYMIRIUM® technology): Low risks of a soil applied nematicide and fungicide to non-target soil invertebrates and bees

Cyclobutrifluram (TYMIRIUM® technology) is a seed- and soil-applied nematicide and fungicide which protects the plant root mass. Cyclobutrifluram acts by inhibiting mitochondrial complex II electron transport and succinate dehydrogenase inhibition (SDHI). Concerns over the potential adverse effects on non-target species were addressed by assessing whether recommended field application rates of cyclobutrifluram would result in adverse impacts on soil invertebrates or honeybees. Studies conducted under laboratory conditions with the active ingredient and two formulations provided No Observed Effect Concentrations for earthworm (Eisenia andreii) reproduction of 71–171 mg a.i./kg dry soil with no effects on soil mite (Hypoaspis aculifier) reproduction. There were no effects on honeybee (Apis mellifera) adults or larvae following chronic exposure to doses up to 400 and 160 mg/kg diet respectively. Using Brazil as a target market (soybean seed treatment and in-furrow application in fruiting vegetables), our laboratory studies indicate that the risk to two species of soil invertebrates and honeybees of the use of cyclobutrifluram either in-furrow or as a seed treatment was orders of magnitude below any levels of concern.

Effects of simulated glyphosate drift to native prairie plants and canola-compatible Brassicaceae species of North Dakota, United States

This study evaluated effects to native plant and weedy Brassicaceae species growing in areas potentially affected by drift of glyphosate used with glyphosate-resistant canola (Brassica napus). Ten native grass and forb species were selected based on importance in prairie areas of North Dakota, US; and four introduced Brassicaceae species (Brassica juncea, Brassica nigra, Brassica rapa, and Sinapis arvensis ssp. arvensis) were selected based on their ability to cross with B. napus. Greenhouse-grown seedlings were treated with 0 (carrier control), 0.00056, 0.0032, 0.018 and 0.1 × a field application rate (FAR) of 829 g ha−1 acid glyphosate (g acid equivalent or a.e. ha−1), along with no spray plants; with each treatment repeated in two experiments. Shoot dry weight and height were measured 14 days after treatment, and data were subjected to analysis of variance or covariance followed by a Dunnett's multiple comparison test to obtain No-Observed-Adverse-Effect-Rates (NOAERs) for both parameters. A Weibull regression was used to obtain the rate producing a 25% reduction (ER25) for shoot dry weight or height for a limited number of species and experiment combinations. Based on NOAER values for both shoot dry weight and height, most native species had reductions in growth with 0.1 × FAR resulting in NOAERs of 0.018 × FAR for at least one experiment. Nassella viridula was the most sensitive native species, with a NOAER of 0.0032 × FAR for shoot dry weight and one experiment for height. The Brassicaceae species responded similarly to glyphosate as the native species, with NOAER values ranging from 0.0032 to 0.018 × FAR. Only four species had valid regression analyses for shoot dry weight or height resulting in ER25 values between 0.007 and 0.054 × FAR. Pascopyrum smithii and Schizachyrium scoparium were not affected by glyphosate as indicated by NOAER values. This study indicated that drift concentrations between approximately 0.003, but more commonly ≥0.1 × FAR (2.49 and 82.9 g ha−1 acid glyphosate, respectively) may affect the growth and potential competitiveness of selected native plant species, and Brassicaceae species sexually compatible with glyphosate-resistant B. napus in North Dakota.

Magneto‐Responsive Bistable Structures with Rate‐Dependent Actuation Modes

AbstractStructural instabilities can be used to provide rapid responses activated by mechanical force or displacement thresholds. The emergence of responsive materials has opened the door for adapting such structural instabilities to actuators that will abruptly deform guided by external stimuli. However, fast configurational transitions between equilibrium states imply important viscoelastic roles at the material level that inevitably scale up to the structural level. A comprehensive understanding of viscoelastic effects is provided on bistable structural transitions combining a new experimental perspective and a thorough modeling analysis. The insights from these results are here translated to magneto‐responsive bistable structures offering a route‐map to design effective actuation conditions. The bistable transition functionally depends on the combination of magnetic field amplitude and application rate. The understanding of the viscoelastic and magneto‐mechanical coupling provides efficient actuation via temporal magnetic pulses, removing the need of generating continued magnetic fields. Finally, these insights are combined to develop a responsive structure whose transient and steady bistable transitions can be modulated by the application rate of external magnetic stimuli.

Efficiency and economic feasibility of using Neonicotinoids against Flat-headed borer Chrysobothris affinis (Fabricius, 1794) (Buprestidae: Coleoptera) infesting Jujube orchards in Basra Province, Iraq

A field study evaluated the efficiency and economic feasibility of using three Neonicotinoids to control Flat-headed borers infesting Jujube orchards in Basra Province during 2020 and 2021. The insecticides tested were Acetamiprid, Imidacloprid and Thiamethoxam, with recommended field application rates. This study showed that Acetamiprid and Imidacloprid provided the best protection to jujube trees, reflected in the high average efficiency (88.70% and 93.40%, respectively). Acetamiprid and Thiamethoxam enhanced the production, with an average of 60.10 and 60.00 kg/tree, respectively, compared to 39.50 kg of the check trees. Thus, the study showed the highest economic return from controlling the flat-headed borers using Acetamiprid and Thiamethoxam (5714900 and 5676500 dinars/ dunum, respectively). In contrast, the economic returns of Imidacloprid were 5082900 Iraqi dinars/ dunum. These results confirmed that the high economic feasibility was related to the efficacy of the low-cost insecticides in reducing the fruit infestation rate and increasing the yield. Keywords: Buprestidae; Insecticides; flat-headed borers; Economic visibility; Neonicotinoids.

Integrating the Soil Microbiota and Metabolome Reveals the Mechanism through Which Controlled Release Fertilizer Affects Sugarcane Growth.

Root-soil underground interactions mediated by soil microorganisms and metabolites are crucial for fertilizer utilization efficiency and crop growth regulation. This study employed a combined approach of soil microbial community profiling and non-targeted metabolomics to investigate the patterns of root-associated microbial aggregation and the mechanisms associated with metabolites under varying controlled-release fertilizer (CRF) application rates. The experimental treatments included five field application rates of CRF (D1: 675 kg/ha; D15: 1012.5 kg/ha; D2: 1350 kg/ha; D25: 1687.5 kg/ha; and D3: 2025 kg/ha) along with traditional fertilizer as a control (CK: 1687.5 kg/ha). The results indicated that the growth of sugarcane in the field was significantly influenced by the CRF application rate (p < 0.05). Compared with CK, the optimal field application of CRF was observed at D25, resulting in a 16.3% to 53.6% increase in sugarcane yield. Under the condition of reducing fertilizer application by 20%, D2 showed a 13.3% increase in stem yield and a 6.7% increase in sugar production. The bacterial ACE index exhibited significant differences between D25 and D1, while the Chao1 index showed significance among the D25, D1, and CK treatments. The dominant bacterial phyla in sugarcane rhizosphere aggregation included Proteobacteria, Actinobacteriota, and Acidobacteriota. Fungal phyla comprised Rozellomycota, Basidiomycota, and Ascomycota. The annotated metabolic pathways encompassed biosynthesis of secondary metabolites, carbohydrate metabolism, and lipid metabolism. Differential analysis and random forest selection identified distinctive biomarkers including Leotiomycetes, Cercospora, Anaeromyxobacter, isoleucyl-proline, and methylmalonic acid. Redundancy analysis unveiled soil pH, soil organic carbon, and available nitrogen as the primary drivers of microbial communities, while the metabolic profiles were notably influenced by the available potassium and phosphorus. The correlation heatmaps illustrated potential microbial-metabolite regulatory mechanisms under CRF application conditions. These findings underscore the significant potential of CRF in sugarcane field production, laying a theoretical foundation for sustainable development in the sugarcane industry.

Chemical and Biological Response of Four Soil Types to Lime Application: An Incubation Study

The soils of four citrus orchards in western Zhejiang were studied in this research. In order to explore the effects of lime on soil chemical properties and bacterial communities, the incubation experiment was conducted with six different dosages of lime addition, 0, 0.6, 1.2, 2.4, 4.8, 7.2 g/kg, respectively. The results showed that soil pH increased significantly (p &lt; 0.05) and the contents of exchangeable acid decreased significantly (p &lt; 0.05) at the early stage of lime application. As time went by, the reacidification existed in the soil of each treatment, mainly reflected in a significant (p &lt; 0.05) decrease in soil pH. Liming increased the nitrate nitrogen content and decreased the ammonium nitrogen content in the four soils. However, the responses of other nutrient indexes to lime varied in different soils, which might be due to the different degrees of soil acidification. In general, the addition of lime increased the soil integrated fertility index (IFI) and improved the soil nutrient status. The application of lime under 2.4 g/kg significantly improved the structure of bacterial community and increased the relative abundance of soil bacterial community species, while the application of lime above 4.8 g/kg might inhibit the growth and activity of microorganisms, resulting in the reduction of soil microbial biomass and diversity. Redundancy analysis (RDA) showed that lime affected the bacterial community mainly by reducing the content of soil active acid and exchangeable acid. At the same time, network analysis showed that the bacterial community had a stronger buffer capacity against external disturbances after lime application. In conclusion, the addition of lime with appropriate amount (2.4~4.8 g/kg, corresponding to a field application rate of 5.8~11.5 t/ha) in acid orchard soil could improve soil properties, soil integrated fertility, and the diversity and stability of the bacterial community.

Recycled Household Ash in Rice Paddies of Bangladesh for Sustainable Production of Rice Without Altering Grain Arsenic and Cadmium

In Bangladesh most agronomic biomass (straw, husk, dried dung) is burnt for domestic cooking use. Consequently, the soil is continuously stripped of mineral nutrients and carbon (C) substrate. Here we investigate if recycling of household ash (ash) as fertilizer can sustainably improve soil fertility as well as minimise accumulation of toxic elements (As, Cd) in rice grain. Large scale field trials across two geographic regions (Barind, Madhupur) and two seasons (wet, dry) and with application of 3 fertiliser treatments (NPKS, ash, NPKS + ash) were conducted. At the end of each season, the impact of region*season*treatment on soil microbial comunities, rice yield, and grain quality (As, Cd, nutrient elements) was assessed. When compared to conventional field application rates of NPKS (control), application of ash boosted rice yield by circa. 20% in both regions during wet and dry season, with no effect on rice grain carcinogenic inorganic arsenic (iAs), dimethylarsonic acid (DMA) or cadmium (Cd), but with potential to increase zinc (Zn). For soil microbial communities, a significant region and season effect as well as correlation with elements in rice grain was observed, amongst these Cd, Zn, iAs and DMA. This study illustrates that application of ash can reduce the requirement for expensive chemical fertiliser, whilst at the same time increasing rice yield and maintaining grain quality, making farming in Bangladesh more sustainable and productive. The study also implies that the combined impact of region, season, and soil microbes determines accumulation of elements in rice grain.

Biochemical responses, feeding and survival in the solitary bee Osmia bicornis following exposure to an insecticide and a fungicide alone and in combination

In agricultural ecosystems, bees are exposed to combinations of pesticides that may have been applied at different times. For example, bees visiting a flowering crop may be chronically exposed to low concentrations of systemic insecticides applied before bloom and then to a pulse of fungicide, considered safe for bees, applied during bloom. In this study, we simulate this scenario under laboratory conditions with females of the solitary bee, Osmia bicornis L. We studied the effects of chronic exposure to the neonicotinoid insecticide, Confidor® (imidacloprid) at a realistic concentration, and of a pulse (1 day) exposure of the fungicide Folicur® SE (tebuconazole) at field application rate. Syrup consumption, survival, and four biomarkers: acetylcholinesterase (AChE), carboxylesterase (CaE), glutathione S-transferase (GST), and alkaline phosphatase (ALP) were evaluated at two different time points. An integrated biological response (IBRv2) index was elaborated with the biomarker results. The fungicide pulse had no impact on survival but temporarily reduced syrup consumption and increased the IBRv2 index, indicating potential molecular alterations. The neonicotinoid significantly reduced syrup consumption, survival, and the neurological activity of the enzymes. The co-exposure neonicotinoid-fungicide did not increase toxicity at the tested concentrations. AChE proved to be an efficient biomarker for the detection of early effects for both the insecticide and the fungicide. Our results highlight the importance of assessing individual and sub-individual endpoints to better understand pesticide effects on bees.

Environmental Impact of Triclopyr on Habitat Quality in Boreal Rights-of-Way.

The indirect effects of herbicides on habitat quality in boreal ecoregions remain poorly understood. Herbicides are commonly applied on boreal rights-of-way to control vegetation below power lines, where they can indirectly enter the soil ecosystem after leaf abscission. Key soil processes such as litter decomposition and soil nutrient cycling can be influenced by altering litter chemistry and/or impacting decomposer species. Disruption of these soil processes could lead to changes in ecosystem health of boreal systems. The indirect impacts of triclopyr on habitat quality of treated boreal rights-of-way were examined through litter mass loss and quality (carbon-to-nitrogen ratios) and the response of boreal invertebrates (Folsomia candida and Oppia nitens) in microcosms and avoidance tests. Litter breakdown rates were not significantly different within a year of treatment. However, we did observe nitrogen profile differences between field-treated and untreated samples, which likely resulted from triclopyr-induced repression of natural leaf senescence processes. At field application rates, there were no differences in survival and reproduction rates of F. candida, which is key in litter breakdown. The triclopyr concentrations that caused 50% of tested F. candida and O. nitens to avoid treated litter were above field application rates. Therefore, field application rates of triclopyr are not expected to impair habitat quality and ecosystem services of boreal ecoregions based on the parameters we evaluated. Our study improves understanding of the effects of herbicide application on habitat quality and is critical for responsible herbicide use on boreal rights-of-way. Environ Toxicol Chem 2022;41:2955-2967. © 2022 SETAC.

Evaluating land application of pulp and paper mill sludge: A review.

It is estimated that >400Mt of board and paper are produced globally per year, and that 4.3-40kg (dw) of sludge like material, pulp and paper mill sludge (PPMS), is generated for every tonne of product. PPMS are now more widely reused in agriculture as a soil amendment due to their high organic content of 40-50% by weight, perceived low toxicity and possible liming capabilities. Within this review article historic and recent literature on PPMS land spreading are combined with knowledge of European and UK regulation to explore the benefits, potential impacts and viability of land spreading PPMS. The review reveals that risks relating to potential N immobilisation in soils post-application can be readily mitigated, if desired, by coapplication of an N source, or even pre-treatment of sludge via composting. The benefits to crops have been demonstrated emphatically, while negative ecological impacts under typical field application rates have not been observed to date. The case is therefore strong for continued land application of the material as an environmentally responsible and sustainable use option. However, there are currently gaps in the literature regarding longer-term implications of PPMS applications in agriculture and in regards to the possible presence of emerging contaminants in some PPMS materials, both of which have been identified as areas that merit further research.

Target-site mutation and cytochrome P450s confer resistance to multiple herbicides in Italian ryegrass (Lolium multiflorum Lam.) from China

Italian ryegrass (Lolium multiflorum Lam.) is a highly competitive grass weed capable of severely infesting wheat fields worldwide. In recent years, Chinese farmers are finding it increasingly difficult to control L. multiflorum when using acetyl-CoA carboxylase (ACCase)-inhibiting herbicides. Accordingly, clarifying the resistance pattern of putative resistant populations of L. multiflorum is important for selecting alternative herbicides for effective weed control. In this study, a putative resistant L. multiflorum population, HN-03, which apparently has survived clodinafop-propargyl treatment under the recommended field application rate, was collected from a wheat field in Zhumadian, Henan, China. Whole-plant bioassay revealed that the HN-03 population had evolved high-level resistance to clodinafop-propargyl. Sequencing of the ACCase gene revealed a point mutation, of TGG to TGT, at codon position 1999, causing a Trp-to-Cys substitution in the resistant plants. The HN-03 population also exhibited cross-resistance to fenoxaprop-P-ethyl, clethodim, and pinoxaden and multiple-resistance to mesosulfuron-methyl and bixlozone, but it remained susceptible to cypyrafluone. Pre-treatment with piperonyl butoxide and malathion considerably increased the susceptibility of the HN-03 population to fenoxaprop-P-ethyl and mesosulfuron-methyl, by 25.3% and 36.6%, respectively. This study shows the L. multiflorum population HN-03 has evolved multiple herbicide resistance due to both a target-site mutation and P450s-mediated enhanced metabolism. Cypyrafluone can be used as an alternative herbicide to control resistant L. multiflorum, and it might be potentially helpful for improving the management of herbicide resistance in other aggressive weeds.

Susceptibility and field exposure of Striacosta albicosta (Lepidoptera: Noctuidae) eggs and larvae in Ontario, Canada to four insecticides.

Striacosta albicosta Smith (Lepidoptera: Noctuidae) is a primary pest of corn, Zea mays L., in the Great Lakes region, causing yield loss and exacerbating mycotoxin contamination of grain. Foliar insecticides are currently used to manage S.albicosta; however, the toxicity and residual activity of these insecticides against S.albicosta are unknown. Laboratory and field bioassays were conducted to determine the susceptibility and period of in-field efficacy provided by chlorantraniliprole, lambda-cyhalothrin, spinetoram, and methoxyfenozide against S.albicosta. Bioassay data were used to simulate management scenarios. For all insecticides tested, 1st instars were highly susceptible to the recommended field application rates and were >3-fold more susceptible to insecticides than 3rd instars. Insecticide activity decreased after application for all insecticides, with chlorantraniliprole having the longest residual activity. In simulated management scenarios where an insecticide was applied at or below the recommended 5% egg mass threshold with additional oviposition, methoxyfenozide application resulted in greater larval survival 14 days after application (DAA) than the other insecticides tested. In scenarios where insecticides were applied 7 days before threshold was reached, all insecticides resulted in larval survival. These data demonstrate that chlorantraniliprole, lambda-cyhalothrin and spinetoram, applied in conjunction with monitoring, provide effective control of S.albicosta larvae for 10-14 days, whereas methoxyfenozide provides effective control for less than 7 days. © 2022 Society of Chemical Industry.

The Value of Hazard Quotients in Honey Bee (Apis mellifera) Ecotoxicology: A Review

Estimates of pesticide application hazards have grown to be one of the most common methodologies for evaluating the impact of pest management practices on honey bees. Typically, hazards are estimated by calculating a Hazard Quotient (HQ), which is based on acute toxicity data for different pesticides and the quantity of those pesticides applied to a field or detected on bees and matrices associated with their hive (honey, wax, pollen, and/or bee bread). Although use of HQ is widespread, there have been few reviews of this methodology, particularly with focus on how effective this method is at predicting effects of pesticides on hives. We evaluated 36 relevant papers, containing calculations of HQ to estimate hazards to honey bees. We observed that HQ was primarily calculated using two different approaches: (1) from the concentration of pesticides in the food, hive, or tissues of honey bees or (2) using the field application rate of the active ingredient as the estimation of pesticide hazard. Within and between HQ calculation methods, thresholds vary widely with some HQ thresholds set below 1 and others set at 10,000. Based on our review we identify key weakness with current HQ methodology and how studies relate HQ to honey bee health endpoints. First, HQ thresholds from studies of pesticides in hives are not based on the same pesticide consumption models from the EPA, potentially overestimating the risk of impacts to colonies. Conversely, HQ estimates calculated from field application rates are not based on eco-toxicological estimates of field exposure, resulting in an overestimation of pesticide reaching colonies. We suggest it is for these reasons that there is poor correspondence between HQ and field-level honey bee health endpoints. Considering these challenges, HQ calculations should be used cautiously in future studies and more research should be dedicated to field level exposure models.

Calibration of laboratory derived indices for non-target arthropod risk assessment with field data for plant protection products

The Hazard Quotient (HQ) compares field application rate to intrinsic toxicity assessed with sensitive indicator species. As a hazard indicator for risk assessment, the HQ must be calibrated against measured effects under field conditions. Because protection goals may be context specific, we analyse how choice of acceptance criteria affects setting of the HQ and calibrate HQ for various scenarios under the strict condition that no false negative conclusions may be reached. We use Non-Target Arthropod toxicity data from laboratory studies on inert (Tier 1) and on natural substrates (Tier 2) and calibrate the HQ using application rates and arthropod abundance counts from field studies in orchards, arable fields, and hay meadows in 34 locations in Western Europe. With 21 formulations (17 active substances) tested in mostly multi-rate field studies, our reference data base has 120/121 values at Tier 1/Tier 2, respectively. We use the Proportion of Affected Taxa and Duration of Effect to jointly define acceptance criteria, starting with No Observed Effects. Absence of field effects is correctly predicted with HQ < 1.3 at Tier 1 and HQ < 0.48 at Tier 2, but these settings result in a high proportion of false positive outcomes. Increasing accepted duration of effect from 0 to 4 to 8 weeks results in HQ-threshold changes from 1.3 to 6.4 to 250 for Tier 1 studies and from 0.48 to 1.1 to 5.7 for Tier 2 studies. This coincides with a clear decrease in false positive outcomes. Recovery within a year is correctly concluded for 73% of the products passing the corresponding Tier 1 HQ < 2600 and for 92% of products at Tier 2 (HQ <230). Our analysis shows that the calibration is appropriate for a broad geographical range, for in-field and off-field situations and for phytophagous and non-phytophagous species alike.

Acute Toxicity of Fungicide-Insecticide-Adjuvant Combinations Applied to Almonds During Bloom on Adult Honey Bees.

Beekeepers report significant honey bee deaths during and after almond bloom. These losses pose a major problem for the California almond industry because of its dependence on honey bees as pollinators. The present study aimed to determine if combinations of pesticides applied during almond bloom during daylight hours were a possible explanation for these losses. In this study we aimed to mimic the spray application route of exposure to pesticides using a Potter Spray Tower to treat adult honey bees with commonly encountered pesticides and pesticide combinations at multiples of the maximum recommended field application rates. Tested insecticides included Altacor® and Intrepid®, and tested fungicides included Tilt®, Pristine®, Luna Sensation®, and Vangard®. Synergistic toxicity was observed when the fungicide Tilt (active ingredient propiconazole) was applied with the insecticide Altacor (chlorantraniliprole), though neither caused significant mortality when applied independently. The study also looked at the effect of adding a spray adjuvant, Dyne‐Amic®, to pesticide mixtures. Dyne‐Amic was toxic to honey bees at concentrations above the maximum recommended field application rate, and toxicity was increased when combined with the fungicide Pristine (pyraclostrobin and boscalid). Addition of Dyne‐Amic also increased toxicity of the Tilt and Altacor combination. These results suggest that application of Altacor and Tilt in combination with an adjuvant at the recommended field application rates could cause mortality in adult honey bees. These findings highlight a potential explanation for honey bee losses around almond bloom, emphasize that the safety of spray adjuvants to bees should not be assumed, and provide support for recommendations to protect bees from pesticides through application at night when bees are not foraging. Environ Toxicol Chem 2022;41:1042–1053. © 2022 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.