Dietary chlorantraniliprole suppresses reproduction in worker bumblebees

Acute oral toxicity and risks of four classes of systemic insecticide to the Common Eastern Bumblebee (Bombus impatiens)

The Common Eastern Bumblebee (Bombus impatiens) is native to North America with an expanding range across Eastern Canada and the USA. This species is commercially produced primarily for greenhouse crop pollination and is a common and abundant component of the wild bumblebee fauna in agricultural, suburban and urban landscapes. However, there is a dearth of pesticide toxicity information about North American bumblebees. The present study determined the acute oral lethal toxicity (48-h LD50) of: the butenolide, flupyradifurone (>1.7 μg/bee); the diamide, cyantraniliprole (>0.54 μg/bee); the neonicotinoid, thiamethoxam (0.0012 μg/bee); and the sulfoximine, sulfoxaflor (0.0177 μg/bee). Compared with published honey bee (Apis mellifera) LD50 values, the present study shows that sulfoxaflor and thiamethoxam are 8.3× and 3.3× more acutely toxic to B. impatiens, whereas flupyradifurone is more acutely toxic to A. mellifera. The current rule of thumb for toxicity extrapolation beyond the honey bee as a model species, termed 10× safety factor, may be sufficient for bumblebee acute oral toxicity. A comparison of five risk assessment equations suggested that the Standard Risk Approach (SRA) and Fixed Dose Risk Approach (FDRA) provide more nuanced levels of risk evaluation compared to the Exposure Toxicity Ratio (ETR), Hazard Quotient (HQ), and Risk Quotient (RQ), primarily because the SRA and FDRA take into account real world variability in pollen and nectar pesticide residues and the chances that bees may be exposed to them.

Multiple factors mediate insecticide toxicity to a key predator for cotton insect pest management

Mortality of agricultural pests caused by arthropod predators is a valuable ecosystem service for crop production. The earwig, Euborellia annulipes (Lucas), attacks different pest species in various crop ecosystems, including larvae and pupae of the boll weevil, Anthonomus grandis grandis (Boh.). In this study, multiple factors were assessed to measure the selectivity of insecticides used against sap-sucking and chewing cotton pests for two E. annulipes populations. Nymphs and adults of E. annulipes were exposed to the insecticides in two ways: ingestion of contaminated prey, and contact with dried residues on either inert surfaces or treated plants bearing prey. Pymetrozine, chlorantraniliprole, and spinetoram had little effect on the predator regardless the tested earwig population, life stage with developmental time and survival, or the route of exposure (ingestion and residual). Cyantraniliprole dried-residue impeded nymph to complete development and only 27% of adults survived until 20 days after exposure. Pyriproxyfen was harmless through acute toxicity to nymphs and adult earwigs (70-100% survival 72 h after exposure), but prevented normal development of nymphs to adults causing chronic toxicity. Chlorfenapyr, indoxacarb, lambda-cyhalothrin, chlorpyrifos, dimethoate, and malathion were harmful to the predator regardless life stage or method of exposure. The negative impact of thiamethoxam, lambda-cyhalothrin and indoxacarb was diminished when exposure occurred on plants with predator allowed to shelter in the soil. The results indicate that insecticide selectivity outcome varies by the insecticide, predator life stage and the predator's behavior. Therefore, testing different predator life stages via several routes of exposure, without denying the insect the opportunity to engage in its normal behavior can provide better estimates of insecticide selectivity.

Whole-Body Acute Contact Toxicity of Formulated Insecticide Mixtures to Blue Orchard Bees (Osmia lignaria)

Blue orchard bees, [Osmia lignaria (Say) (Hymenoptera: Megachilidae)], have been developed as an important pollinator for orchard crops in North America over the last 40 years. The toxicity of several pesticides to O. lignaria and other Osmia species has been previously reported. However, the field-realistic toxicity of formulated premix insecticides comprised of multiple active ingredients (each with a different mode of action) to O. lignaria has not been assessed. Here, we use a customized spray tower in a laboratory setting to assess adult male and female whole-body direct contact exposure to four formulated pesticide mixtures: thiamethoxam + lambda-cyhalothrin (TLC), imidacloprid + beta-cyfluthrin (IBC), chlorantraniliprole + lambda-cyhalothrin (CLC) and methoxyfenozide + spinetoram (MS) by directly spraying anesthetized bees in Petri dishes. Separately, adult male and female whole-body direct contact exposure to formulated imidacloprid (I), beta-cyfluthrin (BC) and their 1:1 binary combination (IBC) was assessed using the same experimental method. Resulting mortality in each study was screened up to 96 h post-treatment to determine acute whole-body contact toxicity. In the first study, TLC and IBC resulted in statistically higher mortality at 24 and 48 h than the two other insecticide combinations tested. The CLC and MS combinations were slower acting and the highest mortality for O. lignaria exposed to these mixtures was recorded at 96 h. We did observe significant differences in toxicity between CLC and MS. In the second study, exposure to the 1:1 binary combination of IBC caused overall significantly higher mortality than exposure to I or BC alone. Both active ingredients alone, however, demonstrated equivalent levels of mortality to the 1:1 binary combination treatment at the 96 h observation reading, indicating increased speed of kill, but not necessarily increased toxicity. Significant differences in the onset of mortality following acute contact whole-body exposure to the formulated insecticide mixtures and individual active ingredients tested were consistently observed across all experiments in both studies.

Benefits of Baculovirus Use in IPM Strategies for Open Field and Protected Vegetables

Widespread use of synthetic chemical insecticides causes growing concern regarding the risks to human health and negative impacts on the environment. At the same time, many insects have become resistant toward synthetic chemical insecticides. Baculoviruses bring many benefits and allow reduced use of synthetic insecticides when included in integrated pest management (IPM). They are specific to their target pest and thus do not have any negative effects on plants, mammals, and non-target insects including natural enemies and pollinators. In addition, their unique mode of action makes them suitable for resistance management. We provide examples of how baculoviruses can be applied in IPM strategies for open field and protected vegetable crops. In field trials, baculovirus products were applied in rotations and tankmixes with chlorantraniliprole, Bacillus thuringiensis products, and spinosad and provided promising control of target pests. The conducted trials in open field and protected vegetables show that baculoviruses can offer an effective solution to control pests in open field and protected vegetable production. Including baculoviruses gave results as good as other application strategies tested while conferring important benefits in reducing residues and improving the resistance management strategy.

Effects of the Neonicotinoid Acetamiprid in Pollen on Bombus impatiens Microcolony Development

Honey bees and other wild bee species including bumble bees have experienced population declines in recent decades. Although many stressors are implicated in bee population declines, much attention has focused on neonicotinoid pesticides, which are widely used and known to be toxic to pollinators. One neonicotinoid, acetamiprid, has been studied very little in bumble bees, despite its use on bumble bee-pollinated crops. We assessed the impacts of acetamiprid to the North American bumble bee Bombus impatiens using the microcolony model. We examined nest growth, development, and subsequent nest productivity as measured by drone production. We found that high concentrations of acetamiprid in pollen (4520 µg/kg) significantly impacted nest growth, development, and, ultimately, reproduction (drone production). We found the no-observable-adverse effect level to be 45.2 µg/kg. Overall, acetamiprid has the potential to negatively impact reproductive endpoints for B. impatiens. However, effects occurred at concentrations substantially higher than expected environmental concentrations that would be achieved when following label rates. Further work is required to assess the effects of this pesticide on B. impatiens via alternate routes of exposure and on queenright colonies. Environ Toxicol Chem 2020;39:2560-2569. © 2020 SETAC. This article has been contributed to by US Government employees and their work is in the public domain in the USA.

The Importance of Males to Bumble Bee (Bombus Species) Nest Development and Colony Viability

Bumble bee population declines over the last decade have stimulated strong interest in determining causative factors and necessary conservation measures. Research attention has largely been directed toward bumble bee worker and queen health and their contributions to population stability, while male bees (i.e., drones) have typically been overlooked regarding their role in influencing colony fitness and longevity. In this review we assess existing literature on the diverse role of males within bumble bee nests and their importance to queen health and fitness, as well as to overall nest success. The implications of reproductive measures, including sperm transfer, mating behavior, mating plugs, and male immunity, among other topics, are examined. Overall, bumble bee males are found to drive colony function in a unique manner. Current knowledge gaps pertaining to the role of males are discussed. We highlight the importance of drones to queen success and fitness in many ways, and suggest future research exploring impacts of this often-neglected caste.

Comparative effects of technical-grade and formulated chlorantraniliprole to the survivorship and locomotor activity of the honey bee, Apis mellifera (L.)

BACKGROUND

The loss of honey bee colonies is a nationally recognized problem that demands attention from both the scientific community and the beekeeping industry. One outstanding threat is the unintended exposure of these pollinators to agricultural pesticides. Anthranilic diamides, such as chlorantraniliprole, are registered for use in stone and pome fruits, vegetables, turf, and grains. There are few publicly available studies that provide an analysis of chlorantraniliprole effects on the survivorship and locomotion activity of beneficial, pollinating insects such as honey bees. The data gathered in this study provide the acute toxicity, 30-day survivorship, and locomotor activity of honey bees exposed to technical-grade chlorantraniliprole and three formulated products with chlorantraniliprole as the active ingredient.

RESULTS

Neither the technical-grade nor the formulated products of chlorantraniliprole were acutely toxic to honey bees following 4 or 72h treatments at the tested concentrations. A 4 h treatment of technical-grade and formulated chlorantraniliprole did not significantly affect the 30-day survivorship, although significantly higher mortality was observed after 30 days for bees receiving a 72 h treatment of technical-grade chlorantraniliprole and two formulated products. The locomotion activity, or total walking distance, of bees receiving a 4 h treatment of one chlorantraniliprole formulation was significantly reduced, with these individuals recovering their normal locomotion activity at 48 h post exposure. Conversely, there was observed lethargic behavior and significantly reduced walking distances for bees provided with a 72 h treatment of technical-grade chlorantraniliprole and each formulated product.

CONCLUSION

This study provides evidence for the effect of long-term exposure of chlorantraniliprole on the survivorship and locomotor activity of honey bees. Bees receiving a more field-relevant short-term exposure survived and moved similarly to untreated bees, reiterating the relative safety of chlorantraniliprole exposure to adult honey bees at recommended label concentrations. © 2020 Society of Chemical Industry.

Development and validation of a method for the analysis of five diamide insecticides in edible mushrooms using modified QuEChERS and HPLC-MS/MS

In this study, a new method for simultaneous determination of cyantraniliprole, chlorantraniliprole, tetrachlorantraniliprole, cyclaniliprole and flubendiamide in edible mushrooms by high-performance liquid chromatography coupled to tandem mass spectrometry (HPLC-MS/MS) combined with a modified QuEChERS procedure. The samples were extracted using acetonitrile and then cleaned up by primary secondary amine (PSA) and octadecylsilane (C18). The determination of these insecticides was achieved in less than 5 min using an electrospray ionization source in positive mode (ESI+) for cyantraniliprole and chlorantraniliprole, while negative mode (ESI-) for tetrachlorantraniliprole, cyclaniliprole and flubendiamide. The linearities of the calibrations for all target compounds were acceptable (R² ≥ 0.9922). The limits of detection and quantification were 0.05-2 μg kg^-1 and 5 μg kg^-1, respectively. Acceptable recoveries (73.5-110.2%) were acquired for these insecticides with RSDs less than 12.7%. The results demonstrated that the proposed method was effective and convenient for the determination of these insecticides in edible mushrooms.

Impact of Diflubenzuron on Bombus impatiens (Hymenoptera: Apidae) Microcolony Development

Reliance on the honey bee as a surrogate organism for risk assessment performed on other bees is widely challenged due to differences in phenology, life history, and sensitivity to pesticides between bee species. Consequently, there is a need to develop validated methods for assessing toxicity in non-Apis bees including bumble bees. The usefulness of small-scale, queenless colonies, termed microcolonies, has not been fully investigated for hazard assessment. Using the insect growth regulator diflubenzuron as a reference toxicant, we monitored microcolony development from egg laying to drone emergence using the Eastern bumble bee Bombus impatiens (C.), a non-Apis species native to North America. Microcolonies were monitored following dietary exposure to diflubenzuron (nominal concentrations: 0.1, 1, 10, 100, and 1,000 µg/liter). Microcolony syrup and pollen consumption was significantly reduced by diflubenzuron exposure. Pupal cell production was also significantly decreased at the highest diflubenzuron concentration assessed. Ultimately, diflubenzuron inhibited drone production in a concentration-dependent manner and a 42-d 50% inhibitory concentration (IC50) was determined. None of the dietary concentrations of diflubenzuron tested affected adult worker survival, or average drone weight. These data strengthen the foundation for use of this methodology, and provide valuable information for B. impatiens; however, more work is required to better understand the utility of the bumble bee microcolony model for pesticide hazard assessment.

Sublethal effects of anthranilic diamide insecticides on the demographic fitness and consumption rates of the Coccinella septempunctata (Coleoptera: Coccinellidae) fed on Aphis craccivora

As for developing effective integrated pest management (IPM), it is necessary to understand the sublethal effects of common insecticides on the non-target beneficial arthropods. In this lab-scale study, the sublethal effects of two anthranilic diamide insecticides chlorantraniliprole and cyantraniliprole on the populations of 7-spot ladybird Coccinella septempunctata (Coleoptera: Coccinellidae) were determined and compared using an age-stage, TWO-SEX life table and CONSUME-MSChart computer program. Cyantraniliprole at low-lethal concentrations of 1 and 10 mg L^-1 significantly prolonged the larval stages and reduced the total adult longevity, compared with the control. Additionally, the net reproductive rate (R₀), intrinsic rate of increase (r), finite rate of increase (λ), and mean generation time (T) were significantly reduced in the group treated with 10 mg L^-1 of cyantraniliprole. Similarly, the net predation (C₀), the finite predation rate (ω), and stable predation rate (ψ) were significantly reduced by cyantraniliprole at 1 and 10 mg L^-1. In contrast, no significant difference in the demographic parameters above was determined for chlorantraniliprole at 1 mg L^-1. Therefore, C. septempunctata population may develop faster and possess greater predation potential against aphids under the exposure of chlorantraniliprole, compared to cyantraniliprole. Chlorantraniliprole may be a preference to cyantraniliprole as a combined alternative with ladybeetle predators in IPM framework.

Honeybee survival and flight capacity are compromised by insecticides used for controlling melon pests in Brazil

The extensive use of insecticides can cause adverse side effects on pollinators, which negatively impact crop productivity. The pollination carried out by the honeybee Apis mellifera L. (Hymenoptera: Apidae) is crucial in increasing the productivity of the melon (Cucumis melo L.). The main objective of this study was to assess if insecticides applied in the cultivation of cantaloupe melon exhibit significant levels of toxicity toward A. mellifera. We tested the toxicity of azadirachtin, pyriproxyfen, chlorantraniliprole, and imidacloprid, which are commonly sprayed to manage melon pests such as the whitefly Bemisia tabaci (Genn.) (Hemiptera: Aleyrodidae), the pickleworm Diaphania nitidalis (Stoll) and the melonworm Diaphania hyalinata (L.) (Lepidoptera: Pyralidae). Three treatments were carried out, 0.0×, 0.1x and 1.0x the concentration recommended by the manufacturer for the control of those pests. Repellency tests, analysis of mortality through contact and ingestion, and flight tests were performed. The insecticide imidacloprid caused mortality rates above 90% in all tested exposure pathways, displaying high residue persistence on plants. Although not causing significant mortality in the ingestion test, pyriproxyfen caused significant mortality after exposure through contact, and change in flight ability. Azadirachtin caused mortality in the ingestion test and impaired the flight ability of bees, while chlorantraniliprole only impaired the flight ability. Moreover, bees were not repelled by these insecticides, suggesting that they may collect contaminated food in the field while foraging. Altogether, ecofriendly, alternative pest control options should be developed, as well as the adoption of more selective insecticides, in order to reduce the non-target effects on honeybees and guarantee their pollination services.

Bombus (Hymenoptera: Apidae) Microcolonies as a Tool for Biological Understanding and Pesticide Risk Assessment

Bumble bees provide valuable pollination services to many wild and agricultural plants. Populations of some bumble bee species are in decline, prompting the need to better understand bumble bee biology and to develop methodologies for assessing the effects of environmental stressors on these bees. Use of bumble bee microcolonies as an experimental tool is steadily increasing. This review closely examines the microcolony model using peer-reviewed published literature identified by searching three databases through November 2018. Microcolonies have been successfully used for investigating a range of endpoints including behavior, the gut microbiome, nutrition, development, pathogens, chemical biology, and pesticides/xenobiotics. Methods for the initiation and monitoring of microcolonies, as well as the recorded variables were catalogued and described. From this information, we identified a series of recommendations for standardizing core elements of microcolony studies. Standardization is critical to establishing the foundation needed to support use of this model for biological response investigations and particularly for supporting use in pesticide risk assessment.

Impact of Biotic and Abiotic Stressors on Managed and Feral Bees

Large-scale declines in bee abundance and species richness over the last decade have sounded an alarm, given the crucial pollination services that bees provide. Population dips have specifically been noted for both managed and feral bee species. The simultaneous increased cultivation of bee-dependent agricultural crops has given rise to additional concern. As a result, there has been a surge in scientific research investigating the potential stressors impacting bees. A group of environmental and anthropogenic stressors negatively impacting bees has been isolated. Habitat destruction has diminished the availability of bee floral resources and nest habitats, while massive monoculture plantings have limited bee access to a variety of pollens and nectars. The rapid spread and increased resistance buildup of various bee parasites, pathogens, and pests to current control methods are implicated in deteriorating bee health. Similarly, many pesticides that are widely applied on agricultural crops and within beehives are toxic to bees. The global distribution of honey bee colonies (including queens with attendant bees) and bumble bee colonies from crop to crop for pollination events has been linked with increased pathogen stress and increased competition with native bee species for limited resources. Climatic alterations have disrupted synchronous bee emergence with flower blooming and reduced the availability of diverse floral resources, leading to bee physiological adaptations. Interactions amongst multiple stressors have created colossal maladies hitting bees at one time, and in some cases delivering additive impacts. Initiatives including the development of wild flower plantings and assessment of pesticide toxicity to bees have been undertaken in efforts to ameliorate current bee declines. In this review, recent findings regarding the impact of these stressors on bees and strategies for mitigating them are discussed.

Endocrine disruption and chronic effects of plant protection products in bees: Can we better protect our pollinators?

Exposure to plant protection products (PPPs) is one of the causes for the population decline of pollinators. In addition to direct exposure, pollinators are exposed to PPPs by pollen, nectar and honey that often contain residues of multiple PPPs. While in legislation PPPs are regarded mainly for their acute toxicity in bees, other effects such as neurotoxicity, immunotoxicity, behavioural changes, stress responses and chronic effects that may harm different physiologically and ecologically relevant traits are much less or not regarded. Despite the fact that endocrine disruption by PPPs is among key effects weakening survival and thriving of populations, pollinators have been poorly investigated in this regard. Here we summarize known endocrine disruptive effects of PPPs in bees and compare them to other chronic effects. Endocrine disruption in honey bees comprise negative effects on reproductive success of queens and drones and behavioural transition of nurse bees to foragers. Among identified PPPs are insecticides, including neonicotinoids, fipronil, chlorantraniliprole and azadirachtin. So far, there exists no OECD guideline to investigate possible endocrine effects of PPPs. Admittedly, investigation of effects on reproduction success of queens and drones is rarely possible under laboratory conditions. But the behavioural transition of nurse bees to foragers could be a possible endpoint to analyse endocrine effects of PPPs under laboratory conditions. We identified some genes, including vitellogenin, which regulate this transition and which may be used as biomarkers for endocrine disruptive PPPs. We plea for a better implementation of the adverse outcome pathway concept into bee's research and propose a procedure for extending and complementing current assessments, including OECD guidelines, with additional physiological and molecular endpoints. Consequently, assessing potential endocrine disruption in pollinators should receive much more relevance.

Pesticide residue survey of pollen loads collected by honeybees (Apis mellifera) in daily intervals at three agricultural sites in South Germany

In agricultural landscapes honeybees and other pollinators are exposed to pesticides, often surveyed by residue analysis of bee bread. However, bee bread is a mixture of pollen pellets of different plants collected over a longer time period. Therefore, pesticide content in the hive varies with plant species and time of pollen collection. Hence, the analysis of bee bread is an approximate approach to gain information on detailed pesticide exposure during the agronomic active season. As high-resolution data is missing, we carried out a pesticide residue survey over five years (2012–2016) of daily collected pollen pellets at three agricultural distinct sites in southern Germany. 281 single day pollen samples were selected and subjected to a multi-pesticide residue analysis. Pesticide contaminations of pollen differed between the sites. Intensive pesticide exposure can be seen by high pesticide concentrations as well as a high amount of different pesticides detected. During the five years of observation 73 different pesticides were found, of which 84% are characterized as non-harmful to honeybees. To estimate pesticide risks for honeybees, the pollen hazard quotient (PHQ) was calculated. Even though pesticides were detected in sublethal concentrations, we found substances not supposed to be exposed to honey bees, indicating the necessity for further improvement of seed treatments and increasing awareness of flowering shrubs, field margins and pesticide drift. Additionally, an in-depth analysis of nine pollen samples, divided into sub-fractions dominated by single plant species, revealed even higher concentrations in single crops for some pesticides. We give precise residue data of 1,657 single pesticide detections, which should be used for realistic laboratory and field tests.

Exposure of honey bees (Apis mellifera) to different classes of insecticides exhibit distinct molecular effect patterns at concentrations that mimic environmental contamination

Pesticides are implicated in the decline of honey bee populations. Many insecticides are neurotoxic and act by different modes of actions. Although a link between insecticide exposure and changed behaviour has been made, molecular effects underlying these effects are poorly understood. Here we elucidated molecular effects at environmental realistic concentrations of two organophosphates, chlorpyrifos and malathion, the pyrethroid cypermethrin, and the ryanodine receptor activator, chlorantraniliprole. We assessed transcriptional alterations of selected genes at three exposure times (24 h, 48 h, 72 h) in caged honey bees exposed to different concentrations of these compounds. Our targeted gene expression concept focused on several transcripts, including nicotinic acetylcholine receptor α 1 and α 2 (nAChRα1, nAChRα2) subunits, the multifunctional gene vitellogenin, immune system related genes of three immune system pathways, genes belonging to the detoxification system and ER stress genes. Our data indicate a dynamic pattern of expressional changes at different exposure times. All four insecticides induced strong alterations in the expression of immune system related genes suggesting negative implications for honey bee health, as well as cytochrome P450 enzyme transcripts suggesting an interference with metabolism. Exposure to neurotoxic chlorpyrifos, malathion and cypermethrin resulted in up-regulation of nAChRα1 and nAChRα2. Moreover, alterations in the expression of vitellogenin occurred, which suggests implications on foraging activity. Chlorantraniliprole induced ER stress which may be related to toxicity. The comparison of all transcriptional changes indicated that the expression pattern is rather compound-specific and related to its mode of action, but clusters of common transcriptional changes between different compounds occurred. As transcriptional alterations occurred at environmental concentrations our data provide a molecular basis for observed adverse effects of these insecticides to bees.

The efficacy of Beauveria bassiana, jasmonic acid and chlorantraniliprole on larval populations of Helicoverpa armigera in chickpea crop ecosystems

BACKGROUND

A robust integrated pest management (IPM) programme is needed to reduce the use of insecticides in controlling Helicoverpa armigera. Therefore, a 2 year field study was conducted to evaluate the use of alternative control measures (biochemical use) for H. armigera relative to exclusively using chemical insecticides. The entomopathogenic fungus Beauveria bassiana, jasmonic acid and the insecticide chlorantraniliprole were each applied twice during the chickpea growing season.

RESULTS

All three applied materials (either alone or combined) significantly (P ≤ 0.05) reduced the larval population of H. armigera and pod infestation. Effects increased with time, and the maximum difference was observed 7 days after the second application in each year. The lowest numbers of larvae per plant and pod infestation were in the B. bassiana 3.21 × 10⁶ + chlorantraniliprole treatment in both 2009/2010 and 2010/2011 year. The reduction in the larval population and pod infestation increased chickpea yield and the highest yield in both seasons, and the maximum yield was obtained in the B. bassiana 3.21 × 10⁶ + chlorantraniliprole treatment. The populations of natural enemies were highest in the jasmonic acid treatment.

CONCLUSION

The results suggest that B. bassiana, jasmonic acid and chlorantraniliprole may be useful components for the H. armigera IPM strategy. © 2016 Society of Chemical Industry.

Comparison of buckwheat, red clover, and purple tansy as potential surrogate plants for use in semi-field pesticide risk assessments with Bombus impatiens

Background. Bumble bees (Bombus spp.) are important wild and managed pollinators. There is increased interest in incorporating data on bumble bees into risk assessments for pesticides, but standardized methods for assessing hazards of pesticides in semi-field and field settings have not yet been established for bumble bees. During semi-field studies, colonies are caged with pesticide-treated flowering surrogate plants, which must be attractive to foragers to ensure colony exposure to the test compound, and must produce an ample nectar and pollen to sustain colonies during testing. However, it is not known which plant(s) are suitable for use in semi-field studies with bumble bees.

Materials and Methods. We compared B. impatiens foraging activity and colony development on small plots of flowering buckwheat (Fagopyrum esculentum, var. common), red clover (Trifolium pratense), and purple tansy (Phacelia tanacetifolia) under semi-field conditions to assess their suitability as surrogate plants for pesticide risk assessment studies with bumble bees. We also compared the growth characteristics and input requirements of each plant type.

Results. All three plant types generally established and grew well. Red clover and purple tansy experienced significant weed pressure and/or insect pest damage. In contrast, pest pressure was extremely low in buckwheat. Overall, B. impatiens foraging activity was significantly greater on buckwheat plots than red clover or purple tansy, but plant type had no effect on number of individuals produced per colony or colony weight.

Discussion. Because of the consistently high foraging activity and successful colony development observed on buckwheat plots, combined with its favourable growth characteristics and low maintenance requirements, we recommend buckwheat as a surrogate plant for use in semi-field pesticide toxicity assessments with B. impatiens.

Combined Non-Target Effects of Insecticide and High Temperature on the Parasitoid Bracon nigricans

We studied the acute toxicity and the sublethal effects, on reproduction and host-killing activity, of four widely used insecticides on the generalist parasitoid Bracon nigricans (Hymenoptera: Braconidae), a natural enemy of the invasive tomato pest, Tuta absoluta (Lepidoptera: Gelechiidae). Laboratory bioassays were conducted applying maximum insecticide label rates at three constant temperatures, 25, 35 and 40°C, considered as regular, high and very high, respectively. Data on female survival and offspring production were used to calculate population growth indexes as a measure of population recovery after pesticide exposure. Spinetoram caused 80% mortality at 25°C and 100% at higher temperatures, while spinosad caused 100% mortality under all temperature regimes. Cyantraniliprole was slightly toxic to B. nigricans adults in terms of acute toxicity at the three temperatures, while it did not cause any sublethal effects in egg-laying and host-killing activities. The interaction between the two tested factors (insecticide and temperature) significantly influenced the number of eggs laid by the parasitoid, which was the lowest in the case of females exposed to chlorantraniliprole at 35°C. Furthermore, significantly lower B. nigricans demographic growth indexes were estimated for all the insecticides under all temperature conditions, with the exception of chlorantraniliprole at 25°C. Our findings highlight an interaction between high temperatures and insecticide exposure, which suggests a need for including natural stressors, such as temperature, in pesticide risk assessments procedures.

Spatial distribution and sequential sampling plans for Tuta absoluta (Lepidoptera: Gelechiidae) in greenhouse tomato crops

BACKGROUND

The within- and between-plant distribution of the tomato leafminer, Tuta absoluta (Meyrick), was investigated in order to define action thresholds based on leaf infestation and to propose enumerative and binomial sequential sampling plans for pest management applications in protected crops.

RESULTS

The pest spatial distribution was aggregated between plants, and median leaves were the most suitable sample to evaluate the pest density. Action thresholds of 36 and 48%, 43 and 56% and 60 and 73% infested leaves, corresponding to economic thresholds of 1 and 3% damaged fruits, were defined for tomato cultivars with big, medium and small fruits respectively. Green's method was a more suitable enumerative sampling plan as it required a lower sampling effort. Binomial sampling plans needed lower average sample sizes than enumerative plans to make a treatment decision, with probabilities of error of <0.10.

CONCLUSIONS

The enumerative sampling plan required 87 or 343 leaves to estimate the population density in extensive or intensive ecological studies respectively. Binomial plans would be more practical and efficient for control purposes, needing average sample sizes of 17, 20 and 14 leaves to take a pest management decision in order to avoid fruit damage higher than 1% in cultivars with big, medium and small fruits respectively.

Sublethal effects of insecticide seed treatments on two nearctic lady beetles (Coleoptera: Coccinellidae)

Predatory insects often feed on plants or use plant products to supplement their diet, creating a potential route of exposure to systemic insecticides used as seed treatments. This study examined whether chlorantraniliprole or thiamethoxam might negatively impact Coleomegilla maculata and Hippodamia convergens when the beetles consumed the extrafloral nectar of sunflowers grown from treated seed. We reared both species on eggs of Ephestia kuehniella and then switched adult H. convergens to a diet of greenbugs, Schizaphis graminum, in order to induce oviposition in this species. Excised sunflower stems, either treated or control and refreshed every 48 h, were provided throughout larval development, or for the first week of adult life. Exposure of C. maculata larvae to chlorantraniliprole and thiamethoxam applied as seed treatments delayed adult emergence by prolonging the pupal period. When adults were exposed, thiamethoxam reduced the preoviposition period compared to chlorantraniliprole, whereas the latter treatment cause females to produce fewer clutches during the observation period. Larvae of C. maculata did not appear to obtain sufficient hydration from the sunflower stems and their subsequent fecundity and fertility were compromised in comparison to the adult exposure experiment where larvae received supplemental water during development. Exposure of H. convergens larvae to thiamethoxam skewed the sex ratio in favor of females; both materials reduced the egg viability of resulting adults and increased the period required for eclosion. Exposure of H. convergens adults to chlorantraniliprole reduced egg eclosion times compared to thiamethoxam and exposure to both insecticides reduced pupation times in progeny. The results indicate that both insecticides have negative, sublethal impacts on the biology of these predators when they feed on extrafloral nectar of sunflower plants grown from treated seed.

Non-target effects of two sunflower seed treatments on Orius insidiosus (Hemiptera: Anthocoridae)

BACKGROUND

Systemic insecticides used as seed treatments are generally considered to be safe for natural enemies. However, predatory insects may feed directly on plants or use plant products to supplement their diet. This study examined whether chlorantraniliprole or thiamethoxam might negatively impact Orius insidiosus (Say) (Hemiptera: Anthocoridae) when bugs utilize sunflowers grown from treated seed.

RESULTS

When eggs of O. insidiosus were laid in the stems of treated sunflower seedlings (two-leaf stage), thiamethoxam reduced egg viability and the longevity of females hatching from these eggs, whereas chlorantraniliprole reduced female survival. Thiamethoxam, but not chlorantraniliprole, reduced female fertility in six-leaf-stage plants. Nymphs exposed to thiamethoxam-treated seedlings had reduced survival, delayed development and reduced fecundity as adults, relative to other treatments, whereas chlorantraniliprole delayed oviposition. Nymphs exposed to six-leaf-stage plants did not differ from controls in either treatment. Adults exposed to treated plants expressed no significant differences among treatments for any parameter evaluated for either plant growth stage.

CONCLUSION

Thiamethoxam treatment on sunflower seeds caused lethal and sublethal effects on O. insidiosus, whereas chlorantraniliprole was not lethal to any life stage, although sublethal effects were evident. The nymphal stage was most susceptible, and insecticidal toxicity diminished with plant development.

Lethal and sublethal effects of azadirachtin on the bumblebee Bombus terrestris (Hymenoptera: Apidae)

Azadirachtin is a biorational insecticide commonly reported as selective to a range of beneficial insects. Nonetheless, only few studies have been carried out with pollinators, usually emphasizing the honeybee Apis mellifera and neglecting other important pollinator species such as the bumblebee Bombus terrestris. Here, lethal and sublethal effects of azadirachtin were studied on B. terrestris via oral exposure in the laboratory to bring out the potential risks of the compound to this important pollinator. The compound was tested at different concentrations above and below the maximum concentration that is used in the field (32 mg L(-1)). As most important results, azadirachtin repelled bumblebee workers in a concentration-dependent manner. The median repellence concentration (RC50) was estimated as 504 mg L(-1). Microcolonies chronically exposed to azadirachtin via treated sugar water during 11 weeks in the laboratory exhibited a high mortality ranging from 32 to 100 % with a range of concentrations between 3.2 and 320 mg L(-1). Moreover, no reproduction was scored when concentrations were higher than 3.2 mg L(-1). At 3.2 mg L(-1), azadirachtin significantly inhibited the egg-laying and, consequently, the production of drones during 6 weeks. Ovarian length decreased with the increase of the azadirachtin concentration. When azadirachtin was tested under an experimental setup in the laboratory where bumblebees need to forage for food, the sublethal effects were stronger as the numbers of drones were reduced already with a concentration of 0.64 mg L(-1). Besides, a negative correlation was found between the body mass of male offspring and azadirachtin concentration. In conclusion, our results as performed in the laboratory demonstrated that azadirachtin can affect B. terrestris with a range of sublethal effects. Taking into account that sublethal effects are as important as lethal effects for the development and survival of the colonies of B. terrestris, this study confirms the need to test compounds on their safety, especially when they have to perform complex tasks such as foraging. The latter agrees with the recent European Food Safety Authority guidelines to assess 'potentially deleterious' compounds for sublethal effects on behavior.

Methylation and worker reproduction in the bumble-bee (Bombus terrestris)

Insects are at the dawn of an epigenetics era. Numerous social insect species have been found to possess a functioning methylation system, previously not thought to exist in insects. Methylation, an epigenetic tag, may be vital for the sociality and division of labour for which social insects are renowned. In the bumble-bee Bombus terrestris, we found methylation differences between the genomes of queenless reproductive workers and queenless non-reproductive workers. In a follow up experiment, queenless workers whose genomes had experimentally altered methylation were more aggressive and more likely to develop ovaries compared with control queenless workers. This shows methylation is important in this highly plastic reproductive division of labour. Methylation is an epigenetic tag for genomic imprinting (GI). It is intriguing that the main theory to explain the evolution of GI predicts that GI should be important in this worker reproduction behaviour.