Novel indices reveal that pollinator exposure to pesticides varies across biological compartments and crop surroundings

Declines in insect pollinators have been linked to a range of causative factors such as disease, loss of habitats, the quality and availability of food, and exposure to pesticides. Here, we analysed an extensive dataset generated from pesticide screening of foraging insects, pollen-nectar stores/beebread, pollen and ingested nectar across three species of bees collected at 128 European sites set in two types of crop. In this paper, we aimed to (i) derive a new index to summarise key aspects of complex pesticide exposure data and (ii) understand the links between pesticide exposures depicted by the different matrices, bee species and apple orchards versus oilseed rape crops. We found that summary indices were highly correlated with the number of pesticides detected in the related matrix but not with which pesticides were present. Matrices collected from apple orchards generally contained a higher number of pesticides (7.6 pesticides per site) than matrices from sites collected from oilseed rape crops (3.5 pesticides), with fungicides being highly represented in apple crops. A greater number of pesticides were found in pollen-nectar stores/beebread and pollen matrices compared with nectar and bee body matrices. Our results show that for a complete assessment of pollinator pesticide exposure, it is necessary to consider several different exposure routes and multiple species of bees across different agricultural systems.

Heatwave-like events affect drone production and brood-care behaviour in bumblebees

Climate change is currently considered one of the major threats to biodiversity and is associated with an increase in the frequency and intensity of extreme weather events, such as heatwaves. Heatwaves create acutely stressful conditions that may lead to disruption in the performance and survival of ecologically and economically important organisms, such as insect pollinators. In this study, we investigated the impact of simulated heatwaves on the performance of queenless microcolonies of Bombus terrestris audax under laboratory conditions. Our results indicate that heatwaves can have significant impacts on bumblebee performance. However, contrary to our expectations, exposure to heatwaves did not affect survival. Exposure to a mild 5-day heatwave (30-32 °C) resulted in increased offspring production compared to those exposed to an extreme heatwave (34-36 °C) and to the control group (24 °C). We also found that brood-care behaviours were impacted by the magnitude of the heatwave. Wing fanning occurred occasionally at temperatures of 30-32 °C, whereas at 34-36 °C the proportion of workers engaged in this thermoregulatory behaviour increased significantly. Our results provide insights into the effects of heatwaves on bumblebee colony performance and underscore the use of microcolonies as a valuable tool for studying the effects of extreme weather events. Future research, especially field-based studies replicating natural foraging conditions, is crucial to complement laboratory-based studies to comprehend how heatwaves compromise the performance of pollinators. Such studies may potentially help to identify those species more resilient to climate change, as well as those that are most vulnerable.

Chronic cadmium exposure impairs flight behavior by dampening flight muscle carbon metabolism in bumblebees

Cadmium pollution affects the global ecosystem because cadmium can be transferred up the food chain. The bumblebee, Bombus terrestris, is an important insect pollinator. Their foraging activity on flowers exposes them to harmful heavy metals, which damages their health and leads to massive population declines. However, the effects of chronic exposure to heavy metals on the flight performance of bumblebees have not yet been characterized. Here, we studied variation in the flight capacity of bumblebees induced by chronic cadmium exposure at field-realistic concentrations using behavioral, physiological, and molecular approaches. Chronic cadmium exposure caused a significant reduction in the duration, distance, and mean velocity of bumblebee flight. Transcriptome analysis showed that the impairment of carbon metabolism and mitochondrial dysfunction in the flight muscle were the primary causes. Physiological, biochemical, and metabolomic analyses validated disruptions in energy metabolism, and impairments in mitochondrial respiratory chain complexes activities. Histological analysis revealed muscle fiber damage and mitochondrial loss. Exogenous decanoic acid or citric acid partially restored sustained flight ability of bumblebees by mitigating muscle fiber damage and increasing energy generation. These findings provide insights into how long-term cadmium stress affects the flight ability of insects and will aid human muscle or exercise-related disease research.

Dominance of non-wetland-dependent pollinators in a plant community in a small natural wetland in Shimane, Japan

Many wetland plants rely on insects for pollination. However, studies examining pollinator communities in wetlands remain limited. Some studies conducted in large wetlands (> 10 ha) have suggested that wetland-dependent flies, which spend their larval stage in aquatic and semi-aquatic habitats, dominate as pollinators. However, smaller wetlands surrounded by secondary forests are more prevalent in Japan, in which pollinators from the surrounding environment might be important. Additionally, information regarding floral traits that attract specific pollinator groups in wetland communities is scarce. Therefore, this study aimed to understand the characteristics of insect pollinators in a small natural wetland (2.5 ha) in Japan. We examined the major pollinator groups visiting 34 plant species and explored the relationship between the flower visitation frequency of each pollinator group and floral traits. Overall, flies were the most dominant pollinators (42%), followed by bees and wasps (33%). Cluster analysis indicated that fly-dominated plants were the most abundant among 14 of the 34 target plant species. However, 85% of the hoverflies, the most abundant flies, and 82% of the bees were non-wetland-dependent species, suggesting that these terrestrial species likely originated from the surrounding environment. Therefore, pollinators from the surrounding environment would be important in small natural wetlands. Flies tend to visit open and white/yellow flowers, whereas bees tended to visit tube-shaped flowers, as in forest and grassland ecosystems. The dominance of flies in small wetlands would be due to the dominance of flowers preferred by flies (e.g., yellow/white flowers) rather than because of their larval habitats.

PCR-Based Screening of Pathogens in Bombus terrestris Populations of Turkey

PURPOSE

Bumblebees are an important group of insects in the pollination of various vegetables, fruits, oilseeds, legumes, and the fodder crops. Compared to honeybees, they have a wider choice of hosts and a longer flight period. These bees are used especially for the pollination of plants in greenhouses and are commercially produced for this purpose. Recently, serious decreases have been occurring in bumblebee populations due to various reasons such as pathogens, and some of species are even threatened with extinction. Due to the worldwide decline in pollinator insects, determining the distribution and prevalence of bumblebee pathogens is of great importance. Therefore, this study was conducted to determine the incidence and prevalence of pathogens in Turkish bumblebee populations and how much of each pathogen was in bumblebee samples.

METHODS

A total of 172 Bombus terrestris (Linnaeus,1758) samples (21 samples from commercial enterprises, 79 samples from greenhouses and 72 samples from nature) were randomly collected from 3 provinces (Antalya, Mersin and İzmir) where greenhouse cultivation is intensively carried out in Turkey. Eighty-nine of these samples were collected in the spring and eighty-three in the autumn. The presence of four pathogens (Nosema bombi, Crithidia bombi, Apicystis bombi, and Locustacarus buchneri) was investigated by PCR using universal primers.

RESULTS

The overall prevalence of Nosema bombi, Crithidia bombi, Apicystis bombi, and Locustacarus buchneri was determined as 7.55%, 9.3%, 11.62%, and 4.65%, respectively. Co-infections (5.81%) were only detected in wild-caught (nature) samples. C. bombi and A. bombi infections were detected at higher rates in the spring samples than in the autumn samples (p < 0.05). There was no significant difference between the spring and autumn samples with respect to the presence of N. bombi and L. buchneri (p > 0.05).

CONCLUSION

The results obtained could be important in determining the prevalence and spread rates of the bumblebee diseases in Turkey and to determine appropriate protection measures. The information gathered should increase our knowledge about the presence of these pathogens in Turkey and could contribute to improve apiarist's practice. More studies are needed to determine the transmission pathways of these pathogens between the populations. Also, complex pathogen interactions in bumblebee populations should be considered in the future to improve bumblebee health.

A spatially explicit model of landscape pesticide exposure to bees: Development, exploration, and evaluation

Pesticides represent one of the greatest threats to bees and other beneficial insects in agricultural landscapes. Potential exposure is generated through compound- and crop-specific patterns of pesticide use over space and time and unique degradation behavior among compounds. Realized exposure develops through bees foraging from their nests across the spatiotemporal mosaic of floral resources and associated pesticides throughout the landscape. Despite the recognized importance of a landscape-wide approach to assessing exposure, we lack a sufficiently-evaluated predictive framework to inform mitigation decisions and environmental risk assessment for bees. We address this gap by developing a bee pesticide exposure model that incorporates spatiotemporal pesticide use patterns, estimated rates of pesticide degradation, floral resource dynamics across habitats, and bee foraging movements. We parameterized the model with pesticide use data from a public database containing crop-field- and date-specific records of uses throughout our study region over an entire year. We evaluate the model performance in predicting bee pesticide exposure using a dataset of pesticide residues in pollens gathered by bumble bees (Bombus vosnesenskii) returning to colonies across 14 spatially independent landscapes in Northern California. We applied alternative model formulations of pesticide accumulation and degradation, floral resource seasonality, and bee foraging behavior to evaluate different levels of detail for predicting observed pesticide exposure. Our best model explained 73 % of observed variation in pesticide exposure of bumble bee colonies, with generally positive correlations for the dominant compounds. Timing and location of pesticide use were integral, but more detailed parameterizations of pesticide degradation, floral resources, and bee foraging improved the predictions little if at all. Our results suggest that this approach to predict bees' pesticide exposure has value in extending from the local field scale to the landscape in environmental risk assessment and for exploring mitigation options to support bees in agricultural landscapes.

Rotenone impairs brain glial energetics and locomotor behavior in bumblebees

Bumblebees are essential pollinators of both wildflowers and crops and face multiple anthropogenic stressors, particularly the utilization of pesticides. Rotenone is an extensively applied neurotoxic pesticide that possesses insecticidal activities against a wide range of pests. However, whether environmentally realistic exposure levels of rotenone can damage neurons in bumblebee brains is still uncertain. Using single-cell RNA-seq, we revealed that rotenone induced cell-specific responses in bumblebee brains, emphasizing the disruption of energy metabolism and mitochondrial dysfunction in glial cells. Correspondingly, the gene regulatory network associated with neurotransmission was also suppressed. Notably, rotenone could specially reduce the number of dopaminergic neurons, impairing bumblebee's ability to fly and crawl. We also found impaired intestinal motility in rotenone-treated bumblebees. Finally, we demonstrated that many differentially expressed genes in our snRNA-seq data overlapped with rotenone-induced Parkinson's disease risk genes, especially in glial cells. Although rotenone is widely used owing to its hypotoxicity, we found that environmentally realistic exposure levels of rotenone induced disturbed glial energetics and locomotor dysfunction in bumblebees, which may lead to an indirect decline in this essential pollinator.

Flower angle favors pollen export efficiency in the snowdrop Galanthus nivalis (Linnaeus, 1753) but not in the lesser celandine Ficaria verna (Huds, 1762)

Flower angle is crucially important for accurate pollination and flower protection against abiotic factors. Evolutionary factors shaping floral traits are particularly strong for bilaterally symmetric flowers because these flowers require more pollination accuracy than radially symmetrical flowers. We experimentally investigated the flower angle in the snowdrop's (Galanthus nivalis) radially symmetrical, early-blooming downward flowers. Bumblebees were able to gather significantly more pollen grains from downward flowers than from upward flowers, but female traits (fertility in the field) seem unaffected by flower angle. Similar experiments with radially symmetrical, later flowering Lesser celandine (Ficaria verna) upward flowers showed no differences in bees' abilities to gather pollen in upward vs downward-facing flowers. The downward angle of snowdrop flowers is an adaptation that increases the ability of insects to collect more pollen grains under unfavorable early spring weather conditions when pollinators are scarce.

Monitoring metal patterns from urban and agrarian sites using the bumblebee Bombus terrestris as a bioindicator

Honeybees are well-established bioindicators for different types of pollutants. This study aims to establish another species of the Apidae family as a bioindicator, with a distinct behaviour and life cycle. The bumblebee Bombus terrestris was used as a bioindicator for 12 metals. Bumblebee hives were placed at sampling sites in and around the city of Aachen, Germany, and metal concentrations were assessed using ICP-MS. Metal concentrations were compared to those found in honeybees described in the literature. Spatial differences in metal patterns were investigated by comparing two land-use types: urban and agrarian. Seasonal differences were compared by taking samples in spring and summer. All analysed metals were detected above the detection limit and within or even above the concentration range found in honeybees. Significant spatial differences were found for the metalloid B and the metal Cd with higher concentrations at the agrarian sites than the urban sites. Significant seasonal differences were found for 8 metals: Fe, Zn, Cu, Ni, Cd, and As concentrations were higher in summer than in spring, while B and V concentrations were higher in spring. To categorise the results, we applied the honeybee contamination index (HCI) and adapted it to bumblebee purposes. According to the HCI, only one agrarian site showed a high contamination level. This study shows that bumblebees are suitable bioindicators for metals. The obtained data can serve as a first baseline in the establishment of additional monitoring studies or risk assessments.

Moving past neonicotinoids and honeybees: A systematic review of existing research on other insecticides and bees

Synthetic pesticides (e.g. herbicides, fungicides and insecticides) are used widely in agriculture to protect crops from pests, weeds and disease. However, their use also comes with a range of environmental concerns. One key concern is the effect of insecticides on non-target organisms such as bees, who provide pollination services for crops and wild plants. This systematic literature review quantifies the existing research on bees and insecticides broadly, and then focuses more specifically on non-neonicotinoid insecticides and non-honeybees. We find that articles on honeybees (Apis sp.) and insecticides account for 80% of all research, with all other bees combined making up 20%. Neonicotinoids were studied in 34% of articles across all bees and were the most widely studied insecticide class for non-honeybees overall, with almost three times as many studies than the second most studied class. Of non-neonicotinoid insecticide classes and non-honeybees, the most studied were pyrethroids and organophosphates followed by carbamates, and the most widely represented bee taxa were bumblebees (Bombus), followed by leaf-cutter bees (Megachile) and mason bees (Osmia). Research has taken place across several countries, with the highest numbers of articles from Brazil and the US, and with notable gaps from countries in Asia, Africa and Oceania. Mortality was the most studied effect type, while sub-lethal effects such as on behaviour were less studied. Few studies tested how the effect of insecticides were influenced by multiple pressures, such as climate change and co-occurring pesticides (cocktail effects). As anthropogenic pressures do not occur in isolation, we suggest that future research also addresses these knowledge gaps. Given the changing global patterns in insecticide use, and the increasing inclusion of both non-honeybees and sub-lethal effects in pesticide risk assessment, there is a need for expanding research beyond its current state to ensure a strong scientific evidence base for the development of risk assessment and associated policy.

High temperature sensitivity of bumblebee castes and the colony-level costs of thermoregulation in Bombus impatiens

Physiological thermal limits often reflect species distribution, but the role that ambient temperature (Ta) plays in limiting species within their thermal environment remains unclear. Climate change-linked declines in bumblebees, an important pollinator group, leave questions regarding which aspect of their physiology is hindered under high Ta. As a eusocial species, bumblebees utilize their ability to thermoregulate as a superorganism to maintain nest temperature (Tn) within a narrow thermal window to buffer developing larvae from developmental defects. Thermoregulatory behaviours, such as thermogenesis to warm up and fanning to cool down the nest, are energetically expensive and it is uncertain how successful large colonies are at maintaining Tn within its optimal range. Using a common bumblebee species, Bombus impatiens, our study first established the critical thermal limits (CTmax) of workers, queens, drones and larvae to determine which caste is most thermally sensitive to heat. We found that larvae had significantly lower heat tolerance than adults, highlighting the importance of colonial thermoregulation. We then measured the energy expenditure of large colonies under acute thermal stress (5-40 °C) using flow-through respirometry while simultaneously quantifying Tn. Colonies that experienced Ta at or below optimal Tn (≤30 °C) were successful at thermoregulation. At 35 °C and above, however, Tn increased despite high energetic costs to the colony. Together our results demonstrate that high Ta poses a risk to colonies that fail to buffer thermally sensitive larvae from changes in Tn.

Sublethal effects of thiamethoxam on immune system cells in the workers of Bombus terrestris (Hymenoptera: Apidae)

Neonicotinoids harm especially bumblebees and other species in agricultural areas all over the world. The toxic effect of thiamethoxam from the neonicotinoid group has been little studied especially on bees. This research aimed to evaluate the effects of thiamethoxam on the immune system cells of Bombus terrestris workers. Different ratios of 1/1000, 1/100 and 1/10 of the recommended maximum application dose of thiamethoxam formed the experimental groups. Ten foraging workers were used for each dose and control groups. Contamination was ensured by spraying the prepared suspensions at different ratios to the bees for 20 s at a pressure of 1 atm. The effects of thiamethoxam on the structures of immune system cells of bumblebees and the amount of these cells were investigated after 48 h of exposure. In general, anomalies such as vacuolization, cell membrane irregularities and cell shape changes were detected in prohemocyte, plasmatocyte, granulocyte, spherulocyte and oenocytoid in each dose group. Hemocyte area measurements in all groups were examined comparatively between groups. In general, granulocyte and plasmatocyte sizes were decreased, while spherulocyte and oenocytoid were increased. It was also determined that there was a significant decrease in the amount of hemocytes in the 1 mm3 hemolymph as dose increased. The results of the study revealed that sublethal doses of thiamethoxam negatively affected hemocytes and their amounts of B. terrestris workers.

First field-based estimates of bumblebee diapause survival rates showcase high survivorship in the wild

Abstract

Bumblebee (Bombus spp.) queens overwintered in artificial settings tend to have low survival rates, raising concerns that diapause may be a particularly sensitive life cycle stage for this ecologically and economically valuable group of pollinators. However, it remains unclear whether lab-based estimates of diapause survival are comparable to survival rates of natural populations. In this study, we monitored the survival of Bombus impatiens queens overwintering in the field in Ipswich, MA, and conducted a meta-analysis of studies that estimate queen diapause survival in the lab to compare our field-based estimates of survival to those of lab-based studies. We found that queen B. impatiens had relatively high rates of overwintering survival after about six months (> 60%), especially when compared to estimates of six-month survival from lab studies (< 10%). We also observed a trend that broadly corroborates many lab studies of bumblebees, in that overwinter survival of queens was related to colony origin. In addition to providing the first estimate of diapause survival for bumblebee queens in nature, our study emphasizes the need to verify patterns observed in the lab to field-based studies.

Implications for insect conservation

Although protecting target species during sensitive life cycle stages is a fundamental goal of conservation ecology, it is first necessary to identify at what stages of the life cycle populations are most vulnerable. Our results suggest that, at least in some study systems, diapause survival of queen bumblebees in the field may be higher than suggested by lab studies.

Supplementary Information

The online version contains supplementary material available at 10.1007/s10841-023-00478-8.

Signatures of adaptation, constraints, and potential redundancy in the canonical immune genes of a key pollinator

All organisms require an immune system to recognise, differentiate and defend against pathogens. From an evolutionary perspective, immune systems evolve under strong selective pressures exerted by fast-evolving pathogens. However, the functional diversity of the immune system means that different immune components and their associated genes may evolve under varying forms of selection. Insect pollinators, which provide essential ecosystem services, are an important system in which to understand how selection has shaped immune gene evolution as their populations are experiencing declines with pathogens highlighted as a potential contributing factor. To improve our understanding of the genetic variation found in the immune genes of an essential pollinator, we performed whole-genome resequencing of wild-caught Bombus terrestris males. We first assessed nucleotide diversity and extended haplotype homozygosity for canonical bumblebee immune genes finding strongest signatures of positive selection acting on genes involved in pathogen recognition and antiviral defence, possibly driven by growing pathogen spread in wild populations. We also identified immune genes evolving under strong purifying selection, highlighting potential constraints on the bumblebee immune system. Lastly, we highlight potential loss of function alleles present in the immune genes of wild-caught haploid males, suggesting that such genes are potentially less essential for development and survival and represent redundancy in the gene repertoire of the bumblebee immune system. Collectively, our analysis provides novel insights into the recent evolutionary history of the immune system of a key pollinator, highlighting targets of selection, constraints to adaptation, and potential redundancy.

Antibiotics-induced dysbiosis in gut microbiota affects bumblebee health via regulating host amino acid metabolism

The gut bacteria can provide nutrition for the host, and regulate host physiological functions and host behavior. In this study, we specifically examined the important roles of free amino acids in the gut microbiota-host interaction. Bumblebees were treated with different concentrations of antibiotics (ampicillin combined with low/high concentrations of tetracycline). Then the effect of antibiotic treatments on the host body weight, gut microbiota, and the free amino acid profiles in the hindgut, hemolymph and brain of bees was evaluated. The results showed that antibiotic treatments resulted in a significant decrease in the host body weight at 11 days of age, the total bacterial load and the abundance of Bifidobacterium bohemicum and Gilliamella apicola in the bumblebee's hindgut. Additionally, the higher the concentration of antibiotics (tetracycline), the greater their impact on the body weight and intestinal microbiota of bumblebees. Further, we found that antibiotic treatments caused changes of free amino acids in different tissues, especially in the hindgut and hemolymph, including particularly the decrease of several types of essential amino acids and branched-chain amino acids. Our results suggest that the gut microbiota may modulate the host growth via specific essential amino acids and branched-chain amino acids, which further reveals the crucial roles of free amino acids in the gut microbiota-host interplay.

Supplementation in vitamin B3 counteracts the negative effects of tryptophan deficiencies in bumble bees

Increasing evidence highlights the importance of diet content in nine essential amino acids for bee physiological and behavioural performance. However, the 10th essential amino acid, tryptophan, has been overlooked as its experimental measurement requires a specific hydrolysis. Tryptophan is the precursor of serotonin and vitamin B3, which together modulate cognitive and metabolic functions in most animals. Here, we investigated how tryptophan deficiencies influence the behaviour and survival of bumble bees (Bombus terrestris). Tryptophan-deficient diets led to a moderate increase in food intake, aggressiveness and mortality compared with the control diet. Vitamin B3 supplementation in tryptophan-deficient diets tended to buffer these effects by significantly improving survival and reducing aggressiveness. Considering that the pollens of major crops and common plants, such as corn and dandelion, are deficient in tryptophan, these effects could have a strong impact on bumble bee populations and their pollination service. Our results suggest planting tryptophan and B3 rich species next to tryptophan-deficient crops could support wild bee populations.

Field-realistic acute exposure to glyphosate-based herbicide impairs fine-color discrimination in bumblebees

Pollinator decline is a grave challenge worldwide. One of the main culprits for this decline is the widespread use of, and pollinators' chronic exposure to, agrochemicals. Here, we examined the effect of a field-realistic dose of the world's most commonly used pesticide, glyphosate-based herbicide (GBH), on bumblebee cognition. We experimentally tested bumblebee (Bombus terrestris) color and scent discrimination using acute GBH exposure, approximating a field-realistic dose from a day's foraging in a patch recently sprayed with GBH. In a 10-color discrimination experiment with five learning bouts, GBH treated bumblebees' learning rate fell to zero by third learning bout, whereas the control bees increased their performance in the last two bouts. In the memory test, the GBH treated bumblebees performed to near chance level, indicating that they had lost everything they had learned during the learning bouts, while the control bees were performing close to the level in their last learning bout. However, GBH did not affect bees' learning in a 2-color or 10-odor discrimination experiment, which suggests that the impact is limited to fine color learning and does not necessarily generalize to less specific tasks or other modalities. These results indicate that the widely used pesticide damages bumblebees' fine-color discrimination, which is essential to the pollinator's individual success and to colony fitness in complex foraging environments. Hence, our study suggests that acute sublethal exposure to GBH poses a greater threat to pollination-based ecosystem services than previously thought, and that tests for learning and memory should be integrated into pesticide risk assessment.

Results of Ring-Testing of a Semifield Study Design to Investigate Potential Impacts of Crop Protection Products on Bumblebees (Hymenoptera, Apidae) and a Proposal of a Potential Test Design

In Europe, the risk assessment for bees at the European Union or national level has always focussed on potential impacts on honeybees. During the revision of the European Food Safety Authority bee guidance it was explicitly stated that bumblebees and solitary bees should be considered as well and consequently concerns were raised regarding the representativeness of honeybees for these other bee species. These concerns originate from differences in size as well as differences in behavioral and life history traits of other bee species. In response to this concern, the non-Apis working group of the International Commission for Plant-Pollinator Relationships initiated a ring-test of a semifield tunnel study design using the bumblebee Bombus terrestris. Nine laboratories participated, validating and improving the proposed design over a 2-year period. The intention of the ring-test experiments was to develop and if possible, establish a test protocol to conduct more standardized semifield tests with bumblebees. In the present study, the results of the ring-tests are summarized and discussed to give recommendations for a promising experimental design. Environ Toxicol Chem 2022;41:2548-2564. © 2022 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Dual function of a bumblebee (Bombus ignitus) serine protease inhibitor that acts as a microbicidal peptide and anti-fibrinolytic venom toxin

In bee venoms, low-molecular-weight peptides, including serine protease inhibitors (SPIs), exhibit multifunctional activities. Although SPIs in bee venoms are relatively well known, those that function in both the body and secreted venom of bees are not well-characterized. In this study, we identified a bumblebee (Bombus ignitus) SPI (BiSPI) that displays microbicidal and anti-fibrinolytic activities. BiSPI was found to consist of a trypsin inhibitor-like domain containing a P1 site and ten cysteine residues. We observed that the BiSPI gene was ubiquitously transcribed in the body, including the venom glands. In correlation, the BiSPI protein was detected both in the body and secreted venom by using an antibody against a recombinant BiSPI peptide produced in baculovirus-infected insect cells. Recombinant BiSPI exhibited inhibitory activity against trypsin but not chymotrypsin and inhibited microbial serine proteases and plasmin but not elastase or thrombin. Moreover, recombinant BiSPI recognized carbohydrates and bound to fungi and gram-negative and gram-positive bacteria. Consistent with these properties, recombinant BiSPI exhibited microbicidal activities against bacteria and fungi through induction of structural damage by binding to the microbial surfaces. Additionally, recombinant BiSPI inhibited the plasmin-mediated degradation of human fibrin and was thus concluded to exhibit anti-fibrinolytic activity. Moreover, the peptide showed no effect on hemolysis. These findings demonstrate the dual function of BiSPI, which acts as a microbicidal peptide and anti-fibrinolytic venom toxin.

Conservation biology for the commercial insect trade in Japan: agricultural bumblebees and companion insects as examples

Japan imports a wide range of arthropods for industrial use and as companion animals. Such imports may threaten ecosystems locally and in their regions of origin. Two iconic insect imports that pose ecological problems are agricultural bumblebees and companion beetles. Colonies of the bumblebee Bombus terrestris have contributed significantly to agricultural production since they were first brought to Japan in the 1990s. But, in their progressive feralisation, they harm populations of native bumblebees through competition, hybridisation, and the introduction of parasites. They also threaten native plant reproduction. The species is currently permitted for agricultural use only in netted greenhouses. Since 2000, imports of companion beetles have thrived, with an estimated market size of many billions of yen. The popularity of rare species has led to a sharp rise in prices, overhunting, and smuggling from their native countries. These exotic species may also become invasive if they escape into nature. There are no clear restrictions on beetle imports, but a government campaign is aimed to improve ethical standards for breeding. In addition, imported tarantulas, centipedes and scorpions are becoming increasingly popular. These species pose similar threats as imported beetles and bees, but the actual state of importation and breeding is difficult to ascertain. Importing insects into Japan can create the following issues: the overexploitation of rare species collected from their native habitats; the traffic in species of which collection and sale is prohibited; the risk that escaped individuals will breed as invasive species; and the introduction of alien microorganisms and parasites.

Expression profiles of venom components in some social hymenopteran species over different post-capture periods

To explore and compare the expression patterns of venom components depending on post-capture periods, venom gland-specific transcriptome and proteome analyses were conducted for five model hymenopteran species at a series of time points after capture. Venom gland-specific genes with signal sequences were considered as putative venom component genes. Expression patterns of venom gland-specific genes in all the social wasps and bees examined varied considerably depending on the post-capture period. Higher numbers of venom genes exhibited a decreasing expression pattern than an increasing pattern as the capture period increased. For example, genes encoding most of the allergens (dipeptidyl peptidase 4, endocuticle structural glycoprotein, odorant-binding protein, phospholipase A1, A2, B1, serine protease, serine protease inhibitor and venom allergen 5), pain-producing factor (mast cell degranulating peptide), and paralyzing factor (neprilysin) commonly exhibited decreasing expression patterns in all of the hymenopteran species tested, except for some of the major venom genes in Apis mellifera and Bombus ignitus, which showed an increasing pattern. These findings indicate species- or group-specific variations in the expression patterns of major venom genes. Taken together, flash freezing in liquid nitrogen immediately after capture was determined to be the best way to obtain the most natural expression profiles of venom components in social wasp species, thus, enabling a better understanding of the toxic potential of venom in wasp sting accidents. This study provides guidance for establishing optimal protocols for venom gland isolation and venom extraction from wasps and bees that can ensure the most naturally represented venom composition.

Environmental differences explain subtle yet detectable genetic structure in a widespread pollinator

BACKGROUND

The environment is a strong driver of genetic structure in many natural populations, yet often neglected in population genetic studies. This may be a particular problem in vagile species, where subtle structure cannot be explained by limitations to dispersal. Consequently, these species might falsely be considered quasi-panmictic and hence potentially mismanaged. A species this might apply to, is the buff-tailed bumble bee (Bombus terrestris), an economically important and widespread pollinator, which is considered to be quasi-panmictic at mainland continental scales. Here we aimed to (i) quantify genetic structure in 21+ populations of the buff-tailed bumble bee, sampled throughout two Eastern European countries, and (ii) analyse the degree to which structure is explained by environmental differences, habitat permeability and geographic distance. Using 12 microsatellite loci, we characterised populations of this species with Fst analyses, complemented by discriminant analysis of principal components and Bayesian clustering approaches. We then applied generalized dissimilarity modelling to simultaneously assess the informativeness of geographic distance, habitat permeability and environmental differences among populations in explaining divergence.

RESULTS

Genetic structure of the buff-tailed bumble bee quantified by means of Fst was subtle and not detected by Bayesian clustering. Discriminant analysis of principal components suggested insignificant but still noticeable structure that slightly exceeded estimates obtained through Fst analyses. As expected, geographic distance and habitat permeability were not informative in explaining the spatial pattern of genetic divergence. Yet, environmental variables related to temperature, vegetation and topography were highly informative, explaining between 33 and 39% of the genetic variation observed.

CONCLUSIONS

In contrast to previous studies reporting quasi-panmixia in continental populations of this species, we demonstrated the presence of subtle population structure related to environmental heterogeneity. Environmental data proved to be highly useful in unravelling the drivers of genetic structure in this vagile and opportunistic species. We highlight the potential of including these data to obtain a better understanding of population structure and the processes driving it in species considered to be quasi-panmictic.

Supporting wild pollinators in agricultural landscapes through targeted legume mixtures

Insect-pollinated legumes are rich in plant-based proteins making them a vital constituent of sustainable healthy diets for people and livestock. Furthermore, they deliver or support a range of ecosystem services that underpin agricultural production and their prevalence in agricultural landscapes is likely to increase. Under typical implementation and management, the value of legumes to pollinators has, however, been questioned. Through exploring a range of legume crops, grown as monocultures and mixtures, this study aims to identify multifunctional legume cropping systems that optimise forage availability for a diversity of wild pollinators whilst delivering a wide range of agronomic and environmental benefits. This study innovatively explores legume mixtures concurrently with monocultures of the component species using replicated small-plot field trials established in two geographical locations. Observational plots assessed the richness and abundance of floral resources, and wild pollinators (i.e. bumblebees and hoverflies) throughout the peak flowering period. Densely flowering, highly profitable legumes (e.g. Trifolium incarnatum and Trifolium mixes) supported abundant and rich pollinator assemblages. The functional makeup of floral visitors was strongly influenced by flower structure and hoverflies, with their shorter proboscises, were largely constrained to legumes with shallower corolla and open weed species. Floral richness was not a key driver of pollinator assemblages; however, clear intra-specific differences were observed in flowering phenology. Combining functionally distinct legumes with respect to flower structure and phenology, will support a wider suite of pollinating insects and help stabilise the temporal availability of forage. For highly competitive legumes (e.g. Vicia faba and Vicia sativa), planting in discrete patches is recommended to reduce the risk of less competitive species failing in mixtures. Legumes can provide valuable forage for pollinators; however, they fail to meet all resource requirements. They should therefore be used in combination with agri-environmental measures targeted to promote early-season forage (e.g. hedgerows and farm woodlands), open flowers for hoverflies, saprophytic hoverfly larval resources (e.g. ditches and ponds) and nesting habitats (e.g. undisturbed field margins).

Sulfoxaflor and nutritional deficiency synergistically reduce survival and fecundity in bumblebees

A range of anthropogenic factors are causing unprecedented bee declines. Among these drivers the usage of pesticides is believed to be crucial. While the use of key bee-harming insecticides, such as the neonicotinoids, has been reduced by regulatory authorities, novel, less studied substances have occupied their market niche. Understanding the threat of these chemicals to bees is, therefore, crucial to their conservation. Here we focus on sulfoxaflor, a novel insecticide, targeting the same neural receptor as the neonicotinoids. In stark contrast to the growing concerns around its negative impacts on bee health, a recent assessment has resulted in the extension of its authorisations across the USA. However, such assessments may underestimate risks by overlooking interactive impacts of multiple stressors. Here we investigated co-occurring, lethal and sublethal risks of sulfoxaflor and a dietary stress for bumblebees (Bombus terrestris), a key pollinator. Specifically, we employed a novel microcolony design, where, for the first time in bees, pesticide exposure mimicked natural degradation. We orally exposed workers to sulfoxaflor and a sugar-deficient diet in a fully factorial design. Field realistic, worst-case sulfoxaflor exposure caused a sharp increase in bee mortality. At sublethal concentrations, sulfoxaflor negatively affected bee fecundity, but not survival. Nutritional stress reduced bee fecundity and synergistically or additively aggravated impacts of sulfoxaflor on bee survival, egg laying and larval production. Our data show that non-mitigated label uses of sulfoxaflor may have major, yet severely neglected effects on bumblebee health, which may be exacerbated by nutritional stress. By unravelling mechanistic interactions of synergistic risks, our study highlights the need to overcome inherent limitations of Environmental Risk Assessment schemes, which, being based on a "single stressor paradigm", may fail to inform policymakers of the real risks of pesticide use.

Anti-fibrinolytic activity of a metalloprotease inhibitor from bumblebee (Bombus ignitus) venom

Bee venom is a mixture of bioactive components that include proteases and protease inhibitors. A metalloprotease inhibitor has been predicted to be a bumblebee-specific toxin in the venom proteome of Bombus terrestris; however, the identification and functional roles of bee venom metalloprotease inhibitors have not been previously determined. In this study, we identified a bumblebee (B. ignitus) venom metalloprotease inhibitor (BiVMPI) that exhibits anti-fibrinolytic activity. BiVMPI contains a trypsin inhibitor-like cysteine-rich domain that exhibits similarity to inducible metalloprotease inhibitor. Using an anti-BiVMPI antibody raised against a recombinant BiVMPI protein produced in baculovirus-infected insect cells, the presence of BiVMPI in the venom gland and secreted venom of B. ignitus worker bees was confirmed. The recombinant BiVMPI protein demonstrated inhibitory activity against a metalloprotease, trypsin, chymotrypsin, protease K, and plasmin, but not subtilisin A, elastase, or thrombin. Additionally, the recombinant BiVMPI bound to plasmin and inhibited the plasmin-mediated degradation of fibrin, demonstrating an anti-fibrinolytic role for BiVMPI as a bee venom metalloprotease inhibitor. Our results provide the first evidence for the identification and anti-fibrinolytic activity of a metalloprotease inhibitor from bee venom.

Intraspecific convergence of floral size correlates with pollinator size on different mountains: a case study of a bumblebee-pollinated Lamium (Lamiaceae) flowers in Japan

Background

Geographic differences in floral size sometimes reflect geographic differences in pollinator size. However, we know little about whether this floral size specialization to the regional pollinator size occurred independently at many places or occurred once and then spread across the distribution range of the plant species.

Results

We investigated the relationship between the local floral size of flowers and local pollinator size in 12 populations of Lamium album var. barbatum on two different mountains in the Japan Alps. Then, using 10 microsatellite markers, we analyzed genetic differentiation among the 12 populations. The results showed that local floral size was correlated with the average size of relevant morphological traits of the local pollinators: floral size was greater in populations visited frequently by the largest flower visitors, Bombus consobrinus queens, than it was in other populations. We also found that the degree of genetic similarity between populations more closely reflected interpopulation geographic proximity than interpopulation similarity in floral size.

Conclusions

Although genetic similarity of populations was highly associated with geographic proximity, floral size varied independently of geographic proximity and was associated with local pollinator size. These results suggest that in L. album var. barbatum, large floral size evolved independently in populations on different mountains as a convergent adaptation to locally abundant large bumblebee species.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12862-021-01796-8.

IRP30 promotes worker egg-laying in bumblebee, Bombus terrestris (Hymenoptera: Apidae)

Bumblebees are important pollinators that have evolved between solitary and advanced eusocial insects. Compared with advanced honeybees, workers of social bumblebee species are prone to laying eggs during the competition phase, which leads to the end of the colony. Therefore, worker reproductive behavior has become a popular research topic for exploring various biological phenomena. Here, we demonstrate a novel reproduction-related function of an immune response protein-encoding gene (Immune Responsive Protein 30, IRP30) in Bombus terrestris by employing RNA interference (RNAi) and a transgenic Drosophila melanogaster system. The results show that worker egg-laying was significantly affected by IRP30 expression levels (P < 0.01). Compared with those in the dsGFP-treated groups, the first egg-laying time was delayed by 3.7 d and the egg number was decreased by 41% in the dsIRP30-treated group. In addition, the average size of the largest oocyte and the relative mRNA expression levels of Vg (vitellogenin) were significantly reduced in the dsIRP30-treated group (P < 0.05). Cellular localization by immunofluorescence demonstrated that IRP30 has important functions in the germ cells of workers' ovarioles. Overexpression of IRP30 was confirmed to increase the reproductive capability of the transgenic D. melanogaster. In conclusion, IRP30 regulates worker egg-laying by affecting the expression of Vg, the size of the ovary and the formation of the oocyte. These findings provide essential information for understanding the mechanisms underlying worker reproductive regulation.

Parent of origin gene expression in the bumblebee, Bombus terrestris, supports Haig's kinship theory for the evolution of genomic imprinting

Genomic imprinting is the differential expression alleles in diploid individuals, with the expression being dependent on the sex of the parent from which it was inherited. Haig's kinship theory hypothesizes that genomic imprinting is due to an evolutionary conflict of interest between alleles from the mother and father. In social insects, it has been suggested that genomic imprinting should be widespread. One recent study identified parent-of-origin expression in honey bees and found evidence supporting the kinship theory. However, little is known about genomic imprinting in insects and multiple theoretical predictions must be tested to avoid single-study confirmation bias. We, therefore, tested for parent-of-origin expression in a primitively eusocial bee. We found equal numbers of maternally and paternally biased expressed genes. The most highly biased genes were maternally expressed, offering support for the kinship theory. We also found low conservation of potentially imprinted genes with the honey bee, suggesting rapid evolution of genomic imprinting in Hymenoptera.

Functional significance of flower orientation and green marks on tepals in the snowdrop Galanthus nivalis (Linnaeus, 1753)

Flower shapes, colors, sizes and fragrances are shaped mostly for pollinator attraction. Flower phenotypes are, however, subjected to conflicting selection directed by both pollinators and non-pollinating agents. We investigated flower attractiveness to a model pollinator in the snowdrop (Galanthus nivalis L.) under laboratory conditions. Naïve bumblebees (Bombus terrestris L.) showed strong, innate preferences for experimentally altered upward positioned flowers, suggesting that the natural, downward orientation did not evolve to attract pollinators. Experimentally treated green marks on inner tepals decreased pollinator attraction compared with flowers expressing intact marks, suggesting that green marks serve to guide/attract pollinators. Attractiveness of green marks was significantly compromised by flower orientation; green marks were attractive only for untreated downward-oriented flowers, but they did not improve the attractiveness of upward-oriented flowers. Our results suggest that downward flowers in snowdrop evolved under conflicting selection directed by biotic and abiotic factors, and that green marks on inner tepals could evolve later to enhance flower attractiveness.

Obstacle avoidance in bumblebees is robust to changes in light intensity

Flying safely and avoiding obstacles in low light is crucial for the bumblebees that forage around dawn and dusk. Previous work has shown that bumblebees overcome the limitations of their visual system—typically adapted for bright sunlight—by increasing the time over which they sample photons. While this improves visual sensitivity, it decreases their capacity to resolve fast motion. This study investigates what effect this has on obstacle avoidance in flight, a task that requires the bees to reliably detect obstacles in the frontal visual field and to make a timely diversion to their flight path. In both bright and dim light, bumblebees avoided the 5 cm diameter obstacle at a consistent distance (22 cm) although in dim light they approached it more slowly from a distance of at least at least 80 cm. This suggests that bumblebees have an effective strategy for avoiding obstacles in all light conditions under which they are naturally active, and it is hypothesised that this is based on a time-to-contact prediction.

Assessing the acute toxicity of insecticides to the buff-tailed bumblebee (Bombus terrestris audax)

The buff-tailed bumblebee, Bombus terrestris audax is an important pollinator within both landscape ecosystems and agricultural crops. During their lifetime bumblebees are regularly challenged by various environmental stressors including insecticides. Historically the honey bee (Apis mellifera spp.) has been used as an 'indicator' species for 'standard' ecotoxicological testing, but it has been suggested that it is not always a good proxy for other eusocial or solitary bees. To investigate this, the susceptibility of B. terrestris to selected pesticides within the neonicotinoid, pyrethroid and organophosphate classes was examined using acute insecticide bioassays. Acute oral and topical LD50 values for B. terrestris against these insecticides were broadly consistent with published results for A. mellifera. For the neonicotinoids, imidacloprid was highly toxic, but thiacloprid and acetamiprid were practically non-toxic. For pyrethroids, deltamethrin was highly toxic, but tau-fluvalinate only slightly toxic. For the organophosphates, chlorpyrifos was highly toxic, but coumaphos practically non-toxic. Bioassays using insecticides with common synergists enhanced the sensitivity of B. terrestris to several insecticides, suggesting detoxification enzymes may provide a level of protection against these compounds. The sensitivity of B. terrestris to compounds within three different insecticide classes is similar to that reported for honey bees, with marked variation in sensitivity to different insecticides within the same insecticide class observed in both species. This finding highlights the need to consider each compound within an insecticide class in isolation rather than extrapolating between different insecticides in the same class or sharing the same mode of action.

Imidacloprid impairs performance on a model flower handling task in bumblebees (Bombus impatiens)

Bumblebees exposed to neonicotinoid pesticides collect less pollen on foraging trips. Exposed bumblebees are also slower to learn to handle flowers, which may account for reduced pollen collection. It is unclear, however, why neonicotinoid exposure slows learning to handle flowers. We investigated the effect of imidacloprid, a neonicotinoid pesticide, on bumblebee motor learning using a lab model of flower handling. Bumblebees learned to invert inside a narrow tube and lift a petal-shaped barrier to reach a reward chamber. Imidacloprid-exposed bumblebees showed a dose-dependent delay to solve the task, which resulted from reduced switching between behavioural strategies and a subsequent delay in use of the successful strategy. This effect was consistent in colonies exposed at 10 but not 2.6 ppb, suggesting a variable effect on individuals at lower doses. These results help to explain why exposed bumblebees are slow to learn to handle flowers and collect less pollen on foraging trips.

Reproductive isolation in alpine gingers: How do coexisting Roscoea (R. purpurea and R. tumjensis) conserve species integrity?

Multiple barriers may contribute to reproductive isolation between closely related species. Understanding the relative strength of these barriers can illuminate the ecological factors that currently maintain species integrity and how these factors originally promoted speciation. Two Himalayan alpine gingers, Roscoea purpurea and R. tumjensis, occur sympatrically in central Nepal and have such similar morphology that it is not clear whether or how they maintain a distinct identity. Our quantitative measurements of the components of reproductive isolation show that they are, in fact, completely isolated by a combination of phenological displacement of flowering, earlier for R. tumjensis and later for R. purpurea, and complete fidelity of visitation by different pollinator species, bumblebees for R. tumjensis and a long-tongued fly for R. purpurea. Furthermore, the nectar of R. tumjensis flowers is available to the shorter tongued bumblebees while R. purpurea nectar is less accessible, requiring deep probing from long-tongued flies. Although flowering phenology is a strong current barrier that seemingly obviates any need for pollinator discrimination, this current pattern need not reflect selective forces occurring at the initial divergence of R. tumjensis. There has been considerable pollinator switching during the radiation of the Himalayan Roscoea, and the association of flowering time with type of pollinator in these sympatric species may have originated among the earliest or latest flowering individuals or populations of an ancestor to exploit either bumblebee activity early in the breeding season or long-tongued fly abundance later in the season. These two sympatric Roscoea species add to accumulating evidence of the primacy of prezygotic pollination traits in speciation among angiosperms even in the absence of postzygotic incompatibility.

Identification and functional characterisation of a novel N-cyanoamidine neonicotinoid metabolising cytochrome P450, CYP9Q6, from the buff-tailed bumblebee Bombus terrestris

Recent work has shown that two bumblebee (Bombus terrestris) cytochrome P450s of the CYP9Q subfamily, CYP9Q4 and CYP9Q5, are important biochemical determinants of sensitivity to neonicotinoid insecticides. Here, we report the characterisation of a third P450 gene CYP9Q6, previously mis-annotated in the genome of B. terrestris, encoding an enzyme that metabolises the N-cyanoamidine neonicotinoids thiacloprid and acetamiprid with high efficiency. The genomic location and complete ORF of CYP9Q6 was corroborated by PCR and its metabolic activity characterised in vitro by expression in an insect cell line. CYP9Q6 metabolises both thiacloprid and acetamiprid more rapidly than the previously reported CYP9Q4 and CYP9Q5. We further demonstrate a direct, in vivo correlation between the expression of the CYP9Q6 enzyme in transgenic Drosophila melanogaster and an increased tolerance to thiacloprid and acetamiprid. We conclude that CYP9Q6 is an efficient metaboliser of N-cyanoamidine neonicotinoids and likely plays a key role in the high tolerance of B. terrestris to these insecticides.

Nectar yeasts enhance the interaction between Clematis akebioides and its bumblebee pollinator

It has been hypothesised that intense metabolism of nectar-inhabiting yeasts (NIY) may change nectar chemistry, including volatile profile, which may affect pollinator foraging behaviours and consequently plant fitness. However, empirical evidence for the plant-microbe-pollinator interactions remains little known. To test this hypothesis, we use a bumblebee-pollinated vine Clematis akebioides endemic to southwest China as an experimental model plant. To quantify the incidence and density of Metschnikowia reukaufii, a cosmopolitan NIY in floral nectar, a combination of yeast cultivation and microscopic cell-counting method was used. To examine the effects of NIY on plant-pollinator interactions, we used real flowers filled with artificial nectar with or without yeast cells. Then the volatile metabolites produced in the yeast-inoculated nectar were analysed with coupled gas chromatography and mass spectrometry (GC-MS). On average 79.3% of the C. akebioides flowers harboured M. reukaufii, and cell density of NIY was high to 7.4 × 10⁴ cells mm^-3 . In the field population, the presence of NIY in flowers of C. akebioides increased bumblebee (Bombus friseanus) pollinator visitation rate and consequently seed set per flower. A variety of fatty acid derivatives produced by M. reukaufii may be responsible for the above beneficial interactions. The volatiles produced by the metabolism of M. reukaufii may serve as an honest signal to attract bumblebee pollinators and indirectly promote the female reproductive fitness of C. akebioides, forming a potentially tripartite plant-microbe-pollinator mutualism.

Knock-on community impacts of a novel vector: spillover of emerging DWV-B from Varroa-infested honeybees to wild bumblebees

Novel transmission routes can directly impact the evolutionary ecology of infectious diseases, with potentially dramatic effect on host populations and knock‐on effects on the wider host community. The invasion of Varroa destructor, an ectoparasitic viral vector in Western honeybees, provides a unique opportunity to examine how a novel vector affects disease epidemiology in a host community. This specialist honeybee mite vectors deformed wing virus (DWV), an important re‐emerging honeybee pathogen that also infects wild bumblebees. Comparing island honeybee and wild bumblebee populations with and without V. destructor, we show that V. destructor drives DWV prevalence and titre in honeybees and sympatric bumblebees. Viral genotypes are shared across hosts, with the potentially more virulent DWV‐B overtaking DWV‐A in prevalence in a current epidemic. This demonstrates disease emergence across a host community driven by the acquisition of a specialist novel transmission route in one host, with dramatic community level knock‐on effects.

First Record of the Velvet Ant Mutilla europaea (Hymenoptera: Mutillidae) Parasitizing the Bumblebee Bombus breviceps (Hymenoptera: Apidae)

Mutillid wasps are ectoparasitic insects that parasitize the enclosed developmental stages of their hosts. Adults are sexually dimorphic, with brilliantly colored and hardened cuticles. The biology of parasitic mutillid wasps has rarely been addressed. Here, we investigated the parasitization by Mutilla europaea on an important pollinator, Bombus breviceps. The parasitic biology and dispersal ability of M. europaea were observed and tested under experimental conditions. We provide the first record of M. europaea parasitizing B. breviceps in southwestern China. As is the case with other bumblebee species, M. europaea mainly parasitized the puparia of males. The dispersal and invasion ability of this parasite under experimental conditions indicates that it spreads rapidly, as far as 20 m in one week, and invades different hosts (B. breviceps and Bombus haemorrhoidalis). This report not only clarifies the parasitic relationship between M. europaea and B. breviceps, but also has important ecological implications for the conservation of bumblebees in China.

Impact of pre- and post-pollination barriers on pollen transfer and reproductive isolation among three sympatric Pedicularis (Orobanchaceae) species

Pedicularis is the largest genus in the Orobanchaceae (>300) with many species co-occurring and co-blooming in subalpine to alpine meadows in the Himalayas. Although it is well known that different Pedicularis species place pollen on different parts of the same bumblebee's body, thus reducing interspecific pollen transfer, it is not known whether post-pollination components also contribute to reproductive isolation (RI). In this study, we quantified the individual strengths and absolute contributions of six pre- and post-pollination components of RI between three sympatric species in two pairs; Pedicularis gruina × Pedicularis tenuisecta (gru × ten) and Pedicularis comptoniifolia × Pedicularis tenuisecta (com × ten). All three Pedicularis species shared the same Bombus species. Individual foragers showed a high, but incomplete, floral constancy for each species. Therefore, pre-pollination barriers were potentially 'leaky' as Bombus species showed a low but consistent frequency of interspecific visitation. The RI strength of pre-pollination was lower in com × ten than in gru × ten. In contrast, post-pollination barriers completely blocked gene flow between both sets of species pairs. Two post-pollination recognition sites were identified. Late acting rejection of interspecific pollen tube growth occurred in com♀ × ten♂, while seeds produced in bi-directional crosses of gru × ten failed to germinate. We propose that, although floral isolation based on pollen placement on pollinators in the genus Pedicularis is crucial to avoid interspecific pollen transfer, the importance of this mode of interspecific isolation may be exaggerated. Post-pollination barriers may play even larger roles for currently established populations of co-blooming and sympatric species in this huge genus in the Himalayas.

The Single von Willebrand factor C-domain protein (SVC) coding gene is not involved in the hymenoptaecin upregulation after Israeli acute paralysis virus (IAPV) injection in the bumblebee Bombus terrestris

Within insects, inductions of antimicrobial peptides (AMPs) have been reported after different virus challenges. It is believed that this link is not directly induced by the virus itself, but rather indirectly induced by secondary effects of virus infection. Here we explored if direct sensing of the virus could trigger AMP expression. Recently, a cytokine-like molecule vago, a member of the Single von Willebrand factor C-domain (SVC) protein family, has been shown to be induced by virus infection in a Dicer-2 dependent manner. SVCs are also reported to be responsive in relation to multiple environmental challenges including bacterial infections and the nutritional status in the model species Drosophila melanogaster. Within the bumblebee Bombus terrestris only one SVC member has been identified and is proven to be involved in both the host antiviral defense and the basal expression of AMP genes, thereby it is a possible candidate linking virus infection and AMPs induction. Here we showed that the injection of Israeli acute paralysis virus (IAPV) resulted in a higher hymenoptaecin expression at 1dpi. This expression is IAPV specific as neither injection of slow bee paralysis virus (SBPV) nor random dsRNA results in a similar induction at 1dpi. We could not prove that hymenoptaecin expression after IAPV treatment was related to BtSVC, as a silencing experiment did not lower hymenoptaecin induction. This leaves indirect activation by secondary effects of IAPV infection as a mechanism of AMP genes induction, or that IAPV infection influences the AMP expression dynamics which is initially induced by non-virus related triggers.

The complete mitochondrial genome of the bumblebee, Bombus hypocrita sapporensis (Insecta: Hymenoptera: Apidae) from Hokkaido Island, Japan

The complete is mitochondrial genome of the Japanese bumblebee Bombus hypocrita sapporensis from Hokkaido Island, Japan is analysed using next generation sequencing. The mitochondrial genome of B. h. sapporensis was observed to be a circular molecule of 15,835 bp. The average AT content in the B. h. sapporensis mitochondrial genome was 85.53%. It was predicted to contain 13 protein-coding genes (PCGs), 22 tRNA genes, and two rRNA genes, along with one A + T-rich control region. The PCGs had ATA, ATG, or ATT as the initiation codon and were terminated by the typical stop codon TAA, except for Cytb. All the tRNA genes typically formed a cloverleaf secondary structure, except for trnE, trnF, and trnS1. The molecular phylogenetic analysis indicated that the B. h. sapporensis from Hokkaido Island population was most similar to that of the geographically isolated B. h. sapporensis from Rebun Island.

Imidacloprid slows the development of preference for rewarding food sources in bumblebees (Bombus impatiens)

Bee pollination is economically and ecologically vital and recent declines in bee populations are therefore a concern. One possible cause of bee declines is pesticide use. Bumblebees exposed to imidacloprid, a neonicotinoid pesticide, have been shown to be less efficient foragers and collect less pollen on foraging trips than unexposed bees. We investigated whether bumblebees (Bombus impatiens) chronically exposed to imidacloprid at field-realistic levels of 2.6 and 10 ppb showed learning deficits that could affect foraging. Bumblebees were tested for their ability to associate flower colour with reward value in a simulated foraging environment. Bumblebees completed 10 foraging trips in which they collected sucrose solution from artificial flowers that varied in sucrose concentration. The reward quality of each artificial flower was predicted by corolla colour. Unexposed bumblebees acquired a preference for feeding on the most rewarding flower colour on the second foraging trip, while bumblebees exposed at 2.6 and 10 ppb did not until their third and fifth trip, respectively. The delay in preference acquisition in exposed bumblebees may be due to reduced flower sampling and shorter foraging trips. These results show that bumblebees exposed to imidacloprid are slow to learn the reward value of flowers and this may explain previously observed foraging inefficiencies associated with pesticide exposure.

Molecular cloning and characterization of the SIFamide precursor and receptor in a hymenopteran insect, Bombus terrestris

SIFamides (SIFa) are a family of neuropeptides that are highly conserved among arthropods. In insects, this peptide is mainly expressed in four medial interneurons in the pars intercerebralis and affects sexual behavior, sleep regulation and pupal mortality. Furthermore, an influence on the hatching rate has been observed. The first SIFa receptor (SIFR) was pharmacologically characterized in Drosophila melanogaster and is homologous to the vertebrate gonadotropin-inhibitory hormone (GnIH) receptor (NPFFR). In this study, we pharmacologically characterized the SIFR of the buff-tailed bumblebee Bombus terrestris. We demonstrated an intracellular increase in calcium ions and cyclic AMP (cAMP) upon ligand binding with an EC₅₀ value in the picomolar and nanomolar range, respectively. In addition, we studied the agonistic properties of a range of related and modified peptides. By means of quantitative real time PCR (qPCR), we examined the relative transcript levels of Bomte-SIFa and Bomte-SIFR in a variety of tissues.

Systemic Israeli acute paralysis virus (IAPV) infection in bumblebees (Bombus terrestris) through feeding and injection

Israeli acute paralysis virus (IAPV) can cause a systemic infection, resulting in mortality in both Apis and Bombus spp. bees. However, little is known about the virus infection dynamics within bee tissues. Here, we established systemic IAPV infections in reared bumblebee Bombus terrestris workers through feeding and injection and investigated the mortality, tissue tropism and viral localization. Injection of approximately 500 IAPV (IAPV^inj stock) particles resulted in acute infection, viral loads within tissues that were relatively stable from bee to bee, and a distinctive tissue tropism, making this method suitable for studying systemic IAPV infection in bumblebees. Feeding with approximately 1 × 10⁶ particles of the same virus stock did not result in systemic infection. A high-concentration stock of IAPV (IAPV^fed stock) allowed us to feed bumblebees with approximately 1 × 10⁹ viral particles, which induced both chronic and acute infection. We also observed a higher variability in viral titers within tissues and less clear tissue tropism during systemic infection, making feeding with IAPV^fed stock less optimal for studying IAPV systemic infection. Strikingly, both infection methods and stocks with different viral loads gave a similar viral localization pattern in the brain and midgut of bumblebees with an acute infection. The implications of these findings in the study of the local immunity in bees and barriers to oral transmission are discussed. Our data provide useful information on the establishment of a systemic viral infection in bees.

A novel insect-infecting virga/nege-like virus group and its pervasive endogenization into insect genomes

Insects are the host and vector of diverse viruses including those that infect vertebrates, plants, and fungi. Recent wide-scale transcriptomic analyses have uncovered the existence of a number of novel insect viruses belonging to an alphavirus-like superfamily (virgavirus/negevirus-related lineage). In this study, through an in silico search using publicly available insect transcriptomic data, we found numerous virus-like sequences related to insect virga/nege-like viruses. Phylogenetic analysis showed that these novel viruses and related virus-like sequences fill the major phylogenetic gaps between insect and plant virga/negevirus lineages. Interestingly, one of the phylogenetic clades represents a unique insect-infecting virus group. Its members encode putative coat proteins which contained a conserved domain similar to that usually found in the coat protein of plant viruses in the family Virgaviridae. Furthermore, we discovered endogenous viral elements (EVEs) related to virga/nege-like viruses in the insect genomes, which enhances our understanding on their evolution. Database searches using the sequence of one member from this group revealed the presence of EVEs in a wide range of insect species, suggesting that there has been prevalent infection by this virus group since ancient times. Besides, we present detailed EVE integration profiles of this virus group in some species of the Bombus genus of bee families. A large variation in EVE patterns among Bombus species suggested that while some integration events occurred after the species divergence, others occurred before it. Our analyses support the view that insect and plant virga/nege-related viruses might share common virus origin(s).

Male scent-marking pheromone of Bombus ardens ardens (Hymenoptera; Apidae) attracts both conspecific queens and males

To explore the role of the volatiles emitted from male labial gland (LG) of the bumblebee Bombus ardens ardens, we investigated the responses of virgin queens and males to volatiles using a gas chromatography-electroantennographic detector (GC-EAD) system and Y-tube olfactometer. GC-EAD analysis revealed that citronellol, the main compound detected in the male LG, caused clear electrophysiological responses in the antennae of B. a. ardens virgin queens and males although two minor compounds elicited antennal responses when applied in a high concentration. Behavioral tests using a Y-tube olfactometer showed that queens and males were significantly attracted to both LG extracts and citronellol more than to the solvent alone. This is the first study to demonstrate that citronellol as a major compound of male scent-marking pheromone in B. a. ardens functions as a sex attractant for queens. The results also suggest that this compound has another function as a trail marker used by males.

Transcript expression bias of phosphatidylethanolamine binding protein gene in bumblebee, Bombus lantschouensis (Hymenoptera: Apidae)

The phosphatidylethanolamine-binding protein (PEBP) family is a highly conserved group of proteins found in a wide range of organism. It plays an important role in innate immunity of insects. Little is known on the expression characteristic and function of PEBP in bees. In the current study, we cloned the pebp gene and investigated its expression profiles at different developmental stages and reproductive status from bumblebee, Bombus lantschouensis (Vogt), which is one of the most abundant pollinators for wild plants and crops in Northern China. Two transcripts (PEBPX1 and PEBPX2) of the pebp gene were cloned for the first time. The transcript PEBPX2 lacked a signal peptide sequence compared to PEBPX1. The full-length cDNA of these two PEBP transcripts is 1005bp and 915bp, with an open reading frame of 627bp and 549bp, respectively. Transcript PEBPX2 was one order of magnitude more expressed than transcript PEBPX1 at most of the developmental stages and different reproductive status (egg-laying versus non- egg-laying females). Both of the PEBP transcripts were highly expressed in brown-eyed with light and dark pigmented cuticle pupae stages. Quantitative PCR and Western Blot demonstrated that PEBP was significantly up-regulated in egg-laying females. In summary, we suggest that levels of these two PEBPs could be related to the regulation of reproduction in bumblebees. In addition, both transcripts likely play an important role in the metamorphosis developmental stage of bumblebee pupae.

nov.: Four novel Gilliamella species isolated from the bumblebee gut

Spectra of five isolates (LMG 28358^T, LMG 29879^T, LMG 29880^T, LMG 28359^T and R-53705) obtained from gut samples of wild bumblebees of Bombus pascuorum, Bombus lapidarius and Bombus terrestris were grouped into four MALDI-TOF MS clusters. RAPD analysis revealed an identical DNA fingerprint for LMG 28359^T and R-53705 which also grouped in the same MALDI-TOF MS cluster, while different DNA fingerprints were obtained for the other isolates. Comparative 16S rRNA gene sequence analysis of the four different strains identified Gilliamella apicola NCIMB 14804^T as nearest neighbour species. Average nucleotide identity values of draft genome sequences of the four isolates and of G. apicola NCIMB 14804^T were below the 96% threshold value for species delineation and all four strains and G. apicola NCIMB 14804^T were phenotypically distinct. Together, the draft genome sequences and phylogenetic and phenotypic data indicate that the four strains represent four novel Gilliamella species for which we propose the names Gilliamella intestini sp. nov., with LMG 28358^T as the type strain, Gilliamella bombicola sp. nov., with LMG 28359^T as the type strain, Gilliamella bombi sp. nov., with LMG 29879^T as the type strain and Gilliamella mensalis sp. nov., with LMG 29880^T as the type strain.

Diet effects on bumblebee health

Among physiological processes, the maintenance of immunity is one of the most energetically costly in invertebrates. Disease resistance can be quantified by measuring immunocompetence, which is defined as the ability of an organism to mount an immune response, either in cellular, humoral or behavioural forms. In insects, immune capacity can be affected by a variety of factors including pesticides, genetic diversity or diet. Here we focus on an important species of domesticated pollinator, Bombus terrestris, and the potential impact of a poor pollen diet (low nutritional content and toxic) on its health. We investigate three responses at both colony and individual levels: behavioural, humoral and cellular. Our results show that poor pollen diets decrease larval and pupal masses and increase larval ejection as well as adult constitutive immunity (i.e., prophenoloxidase assays). The susceptibility of bumblebees to disease and infection might therefore be greater after a nutritive stress. These findings raise the importance of available plant hosts, especially floral plant species providing pollen with suitable nutritive quality (i.e., nutrient pollen content) for bumblebees.

Comparative phylogeography in the Atlantic forest and Brazilian savannas: pleistocene fluctuations and dispersal shape spatial patterns in two bumblebees

Background

Bombus morio and B. pauloensis are sympatric widespread bumblebee species that occupy two major Brazilian biomes, the Atlantic forest and the savannas of the Cerrado. Differences in dispersion capacity, which is greater in B. morio, likely influence their phylogeographic patterns. This study asks which processes best explain the patterns of genetic variation observed in B. morio and B. pauloensis, shedding light on the phenomena that shaped the range of local populations and the spatial distribution of intra-specific lineages.

Results

Results suggest that Pleistocene climatic oscillations directly influenced the population structure of both species. Correlative species distribution models predict that the warmer conditions of the Last Interglacial contributed to population contraction, while demographic expansion happened during the Last Glacial Maximum. These results are consistent with physiological data suggesting that bumblebees are well adapted to colder conditions. Intra-specific mitochondrial genealogies are not congruent between the two species, which may be explained by their documented differences in dispersal ability.

Conclusions

While populations of the high-dispersal B. morio are morphologically and genetically homogeneous across the species range, B. pauloensis encompasses multiple (three) mitochondrial lineages, and show clear genetic, geographic, and morphological differences. Because the lineages of B. pauloensis are currently exposed to distinct climatic conditions (and elevations), parapatric diversification may occur within this taxon. The eastern portion of the state of São Paulo, the most urbanized area in Brazil, represents the center of genetic diversity for B. pauloensis.

Electronic supplementary material

The online version of this article (doi:10.1186/s12862-016-0803-0) contains supplementary material, which is available to authorized users.

BEESCOUT: A model of bee scouting behaviour and a software tool for characterizing nectar/pollen landscapes for BEEHAVE

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BEESCOUT is a spatially explicit, individual-based model of scouting bees.

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It determines the detection probabilities of food sources.

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It can be linked to the honey bee model BEEHAVE to predict colony development.

Social bees are central place foragers collecting floral resources from the surrounding landscape, but little is known about the probability of a scouting bee finding a particular flower patch. We therefore developed a software tool, BEESCOUT, to theoretically examine how bees might explore a landscape and distribute their scouting activities over time and space. An image file can be imported, which is interpreted by the model as a “forage map” with certain colours representing certain crops or habitat types as specified by the user. BEESCOUT calculates the size and location of these potential food sources in that landscape relative to a bee colony. An individual-based model then determines the detection probabilities of the food patches by bees, based on parameter values gathered from the flight patterns of radar-tracked honeybees and bumblebees. Various “search modes” describe hypothetical search strategies for the long-range exploration of scouting bees. The resulting detection probabilities of forage patches can be used as input for the recently developed honeybee model BEEHAVE, to explore realistic scenarios of colony growth and death in response to different stressors. In example simulations, we find that detection probabilities for food sources close to the colony fit empirical data reasonably well. However, for food sources further away no empirical data are available to validate model output. The simulated detection probabilities depend largely on the bees’ search mode, and whether they exchange information about food source locations. Nevertheless, we show that landscape structure and connectivity of food sources can have a strong impact on the results. We believe that BEESCOUT is a valuable tool to better understand how landscape configurations and searching behaviour of bees affect detection probabilities of food sources. It can also guide the collection of relevant data and the design of experiments to close knowledge gaps, and provides a useful extension to the BEEHAVE honeybee model, enabling future users to explore how landscape structure and food availability affect the foraging decisions and patch visitation rates of the bees and, in consequence, to predict colony development and survival.