Important Crop Pollinators Research Articles

Prior Experience with Food Reward Influences the Behavioral Responses of the Honeybee Apis mellifera and the Bumblebee Bombus lantschouensis to Tomato Floral Scent.

Simple SummaryBees are important pollinators for many agricultural crops. Compared with bumblebees, honeybees are less attracted to tomato flowers. Floral scent usually plays an important role in mediating the foraging behavior of bees, and tomato flowers release special scents. However, little is known about how tomato floral scent regulates the foraging behaviors of these two bee taxa. In the current study, we investigated the foraging behaviors of the widely used pollinator honeybee Apis mellifera and a native bumblebee, Bombus lantschouensis, on tomato flowers to evaluate the potential application of these two bee species for tomato pollination in solar greenhouses. Moreover, we determined whether honeybees and bumblebees show different responses to tomato floral scent and how innate biases and prior experience influence bee choice behavior. We found that naïve bees showed no preference for tomato floral scent but could develop such a preference after learning to associate tomato floral scent with a food reward on the basis of foraging experience or scent-learning procedures. We conclude that scent-learning experiences with food reward can change the innate bias of bees and could be utilized to improve the pollination service efficiency of bees for commercial crops.Bee responses to floral scent are usually influenced by both innate biases and prior experience. Honeybees are less attracted than bumblebees to tomato flowers. However, little is known about how tomato floral scent regulates the foraging behaviors of honeybees and bumblebees. In this study, the foraging behaviors of the honeybee Apis mellifera and the bumblebee Bombus lantschouensis on tomato flowers in greenhouses were investigated. Whether the two bee species exhibit different responses to tomato floral scent and how innate biases and prior experience influence bee choice behavior were examined. In the greenhouses, honeybees failed to collect pollen from tomato flowers, and their foraging activities decreased significantly over days. Additionally, neither naïve honeybees nor naïve bumblebees showed a preference for tomato floral scent in a Y-tube olfactometer. However, foraging experience in the tomato greenhouses helped bumblebees develop a strong preference for the scent, whereas honeybees with foraging experience continued to show aversion to tomato floral scent. After learning to associate tomato floral scent with a sugar reward in proboscis extension response (PER) assays, both bee species exhibited a preference for tomato floral scent in Y-tube olfactometers. The findings indicated that prior experience with a food reward strongly influenced bee preference for tomato floral scent.

An invasive pest of bumblebee: A new record of the tracheal mite Locustacarus buchneri (Acari: Podapolipidae) from the European bumblebee, Bombus terrestris (Hymenoptera: Apidae) in Korea

• Bumblebees ( Bombus spp.) are important pollinators. • The endoparasitic mite, Locustacarus buchneri was discovered from Bombus terrestris. • It is the first report of the genus and species in Korea. • Morphological and molecular characteristics were detailed. • The ecological significances of the finding were discussed. Bumblebees ( Bombus spp.) are important pollinators of agricultural crops and wild plants, especially tomato and sweet pepper species requiring large-sized and buzzing pollinators. The endoparasitic mite Locustacarus buchneri Stammer 1951 (Acari; Podapolipidae) was identified from commercial populations of the introduced European bumblebee Bombus terrestris. We report the genus and species of this mite for the first time in Koran fauna. Identification was based on morphological and molecular characteristics. Morphological details were illustrated and compared with those to the original description. We analyzed partial cytochrome oxidase I gene to understand the phylogenetic relationship and possible source of invention. The maximum likelihood tree and haplotype network revealed that the Korean population is closely related to Japanese population than European population. The ecological significance of this finding and possible consequences of the invasive species to the native species are discussed.

The Neonicotinoid Insecticide Imidacloprid Disrupts Bumblebee Foraging Rhythms and Sleep.

SummaryNeonicotinoids have been implicated in the large declines observed in insects such as bumblebees, an important group of pollinators. Neonicotinoids are agonists of nicotinic acetylcholine receptors that are found throughout the insect central nervous system and are the main mediators of synaptic neurotransmission. These receptors are important for the function of the insect central clock and circadian rhythms. The clock allows pollinators to coincide their activity with the availability of floral resources and favorable flight temperatures, as well as impact learning, navigation, and communication. Here we show that exposure to the field-relevant concentration of 10 μg/L imidacloprid caused a reduction in bumblebee foraging activity, locomotion, and foraging rhythmicity. Foragers showed an increase in daytime sleep and an increase in the proportion of activity occurring at night. This could reduce foraging and pollination opportunities, reducing the ability of the colony to grow and reproduce, endangering bee populations and crop yields.

Annual flowers strips benefit bumble bee colony growth and reproduction

Bumble bees are important crop pollinators but are negatively impacted by agricultural intensification and concomitant loss of floral resources. Flower strips can increase the abundance and sometimes the diversity of bumble bees at local scales, but the importance of flower strips for bumble bee populations at larger scales remains poorly understood. We investigated the effect of flower strips on bumble bee colony growth and reproduction at landscape scales. Commercial bumble bee colonies of a native species (Bombus terrestris) were placed and monitored at different distances from flower strips that were sown on existing ecological focus areas (European Common Agricultural Policy) in southern Sweden. Both the average colony growth (weight) and the production of reproductives (drones and queens) were highest for colonies adjacent to flower strips and declined with increasing distance. Colonies close to the flower strip also produced more reproductives per colony weight. Colony foraging activity was negatively related to the distance to flower strips whereas worker size was not affected. Annual flower strips in ecological focus areas benefit bumble bee colonies by increasing foraging success, colony growth and finally boosting sexual reproduction, demonstrating potential benefits for pollination within and between seasons. These effects were spatially limited but extended to foraging ranges of bumble bees. However, effects of increased colony growth on the abundance of foraging bees in the landscape may extend to larger distances because of forager movements within seasons and queen dispersal between seasons, suggesting that voluntary or incentivised collaboration between farmers may be needed to achieve optimal implementation of flower strips.

Mitochondrial genomes illuminate the evolutionary history of the Western honey bee (Apis mellifera)

Western honey bees (Apis mellifera) are one of the most important pollinators of agricultural crops and wild plants. Despite the growth in the availability of sequence data for honey bees, the phylogeny of the species remains a subject of controversy. Most notably, the geographic origin of honey bees is uncertain, as are the relationships among its constituent lineages and subspecies. We aim to infer the evolutionary and biogeographical history of the honey bee from mitochondrial genomes. Here we analyse the full mitochondrial genomes of 18 A. mellifera subspecies, belonging to all major lineages, using a range of gene sampling strategies and inference models to identify factors that may have contributed to the recovery of incongruent results in previous studies. Our analyses support a northern African or Middle Eastern origin of A. mellifera. We show that the previously suggested European and Afrotropical cradles of honey bees are the result of phylogenetic error. Monophyly of the M, C, and O lineages is strongly supported, but the A lineage appears paraphyletic. A. mellifera colonised Europe through at least two pathways, across the Strait of Gibraltar and via Asia Minor.

Nocturnal vs. Diurnal Pollination of Self-Fertile Peaches and Muscadine Grapes

There is growing evidence that nocturnal moths are important pollinators of agricultural crops. However, the contribution of these pollinators to the production of crops remains largely unknown. We explored the pollination input nocturnal insects provide to self-fertile varieties of peaches and muscadine grapes. Our goal was to determine if these fruit varieties need little or no input from insect pollinators, as previously believed, or if pollination is provided by the oft-ignored nocturnal-insect pollinators. Moths were anecdotally observed to be the dominant floral visitor in peaches, diurnal or nocturnal. No floral visitors were recorded in muscadine grapes. We found that the fruit set of self-fertile varieties of both fruits was not significantly increased by any pollinator group, suggesting that pollination contribution provided by insects was unnecessary. Interestingly, we observed both common moth visitors to consistently vibrate their wings during floral visits. This behavior is known to increase body temperature in moths for flight, but this is the first time the vibration behavior has been associated with floral visitation. While the examined fruit varieties received no benefit from insect pollination, important observations highlight our lack of understanding concerning nocturnal pollination and require focused research to elucidate.

Near-natural habitats near almond orchards with presence of empty gastropod shells are important for solitary shell-nesting bees and wasps

Solitary bees serve as important native pollinators of wild plants and crops. Several species of bees, which form strong populations in open habitats of European landscapes, nest in empty snail shells. In the present study, we focused on shell-nesting bees in near-natural habitats neighbouring almond orchards near the town Lleida in north-east Spain. We performed a series of manipulative experiments, which aimed to elucidate the importance of empty shells of four common large- and medium-sized gastropod species for nesting bees in near-natural and ruderal habitats surrounding the almond orchards. We also matched these data with findings of bees in naturally occurring shells at each examined site. All study sites consisted of habitats with naturally present shells and evidence of the natural presence of the study species of bees. In total, we recorded 15 nesting bee and wasp species and eight species of hymenopteran parasites in collected shells, one of which, the spider wasp Priocnemis propinqua, was recorded nesting in empty gastropod shells for the first time. In total, the deployed shells hosted eight nesting species and two species of parasitic Hymenoptera. The prevalence of nests in experimentally deployed shells was low, with only a single nest present near irrigated orchards. The abundance of nests was also low at sites where the naturally present shells were highly abundant. Combined, available evidence suggests the importance of near-natural habitats for the presence of shell-nesting bees and wasps in South-European landscapes. The abundance of shell nesting bees and wasps does not increase proportionally with the increase in empty snail shell abundance and other factors should be considered limiting at such sites.

Diversity of pollen sources used by managed honey bees in variegated landscapes

Honey bees are the most economically important crop pollinator worldwide. They depend on a diversity of pollen for reproduction and colony growth. However, the influence of landscape composition on diversity and quantity of pollen collection by honey bees remains largely unexplored, particularly in variegated landscapes. Pollen on honey bees was trapped from 41 hives across ten sites in the Western Cape, South Africa during summer. Sampled hives were near eucalyptus trees surrounded by a high percentage of natural vegetation. Hives could therefore potentially be presented with a diverse range of flowers. To obtain a measure of relative abundance and representation of plant taxa pollen samples were collected at hives, sorted by color, weighed and DNA barcoded. Landscape analysis was performed to estimate the relative availability of the main floral resource-types and how this influenced the composition of pollen collected. Overall, eucalyptus made up the largest portion (∼49%) of pollen loads, the remainder was composed of 31 other taxa (12% native and 39% alien plants). An increase in the area of eucalyptus resulted in an increased as well as the relative amount of eucalyptus and natural pollen collected. Conversely, an increase in the area of eucalyptus resulted in a decrease in alien plant pollen and vice versa. Our results provide important quantitative evidence that shows the amount and diversity of pollen used by honey bees in summer appears to be disproportionately met by human-modified landscapes; whereas, natural vegetation, despite its large extent and diversity, performs a lower-level role during this season.

Analyzing the Dietary Diary of Bumble Bee.

Bumble bees are important crop pollinators and provide important pollination services to their respective ecosystems. Their pollen diet and thus food preferences can be characterized through nucleic acid sequence analysis. We present ITS2 amplicon sequence data from pollen collected by bumble bees. The pollen was collected from six different bumble bee colonies that were placed in independent agricultural landscapes. We compared next-generation (Illumina), i.e., short-read, and third-generation (Nanopore), i.e., MinION, sequencing techniques. MinION data were preprocessed using traditional and Nanopore specific tools for comparative analysis and were evaluated in comparison to short-read sequence data with conventional processing. Based on the results, the dietary diary of bumble bee in the studied landscapes can be identified. It is known that short reads generated by next-generation sequencers have the advantage of higher quality scores while Nanopore yields longer read lengths. We show that assignments to taxonomic units yield comparable results when querying against an ITS2-specific sequence database. Thus, lower sequence quality is compensated by longer read lengths. However, the Nanopore technology is improving in terms of data quality, much cheaper, and suitable for portable applications. With respect to the studied agricultural landscapes we found that bumble bees require higher plant diversity than only crops to fulfill their foraging requirements.

Characteristics of the Two Asian Bumblebee Species Bombus friseanus and Bombus breviceps (Hymenoptera: Apidae).

This study compared the food plants, life cycle, colony development, and mating behaviour of the two Asian bumblebee species Bombus friseanus and B. breviceps, which are very important pollinators for many wild flowers and crops in local ecosystems. Both species were shown to be highly polylectic. Differences were observed in their life cycles and colony development patterns. The colony foundation rate of the field-collected queens was high in both species, 95.5% in B. friseanus and 86.5% in B. breviceps. The intervals from colony initiation to colony sizes of 30, 60, and 80 workers and to the first male and gyne emergence were significantly shorter in B. friseanus than in B. breviceps (p < 0.01). The development period of the first batch of workers showed no significant difference between the two species (p > 0.05). Compared with B. friseanus, B. breviceps produced remarkably higher numbers of workers (135 ± 30 workers/colony in B. friseanus and 318 ± 123 workers/colony in B. breviceps) and males (199 ± 46 males/colony in B. friseanus and 355 ± 166 males/colony in B. breviceps) (p < 0.01), with notable variation was found among the colonies in both species. With no significant difference in the mating rate between these two species, the copulation duration of B. breviceps (1.54 ± 0.63 min) was strikingly shorter than that of B. friseanus (27.44 ± 11.16 min) (p < 0.001). This study highlights the characteristics of the two Asian bumblebee species and will aid further studies on their conservation and agricultural pollination use.

Native honeybees as flower visitors and pollinators in wild plant communities in a biodiversity hotspot

AbstractWestern honeybees (Apis mellifera L.), native to Europe and Africa, have been transported worldwide and are now one of the most important global crop pollinator species. Although the relative contribution of honeybees to global crop pollination is increasingly recognized, relatively little is known about their importance as pollinators in wild plant communities. The only remaining wild and unmanaged western honeybee populations are in Africa. We investigated the importance of honeybees as pollinators of diverse wild plant communities in two protected areas within the Maputaland–Pondoland–Albany biodiversity hotspot in South Africa. Sites were far from any known areas of beekeeping, and so all honeybees were most likely from wild colonies. Honeybees visited a large proportion of flowering plant species within these two communities (40% and 35%) and also provided a substantial proportion of visits to the plants they visited (40% and 32%, respectively). However, when pollinator importance indices (based on abundance and the size and purity of pollen loads) were calculated for a small subset of plants, honeybees were only important pollinators of 29% of the plants they visited. Our data provide a first step in determining the importance of honeybees as flower visitors and pollinators in wild plant communities and the potential impacts of honeybee declines on these highly diverse grassland ecosystems. Our work suggests that many plants in the grassland systems studied are visited by non‐Apis flower visitors and therefore that conservation efforts should also focus on these pollinator groups.

How much do rare and crop‐pollinating bees overlap in identity and flower preferences?

Abstract The biodiversity‐centred approach to conservation prioritizes rare species, whereas the ecosystem services approach prioritizes species that provide services to people. The two approaches align when rare species provide ecosystem services, or when both groups of species benefit from the same management action. We use data on bee pollinators and the plant species they forage on to determine if there are rare species among the most important crop pollinators, and the extent to which plant species selected to support crop pollinators would support rare species as well. We used pre‐existing, regional‐scale datasets to determine which bee species are regionally rare, and which are regionally important crop pollinators. To assess the plant preferences of these two groups of bee species, we collected two datasets on plant–pollinator interactions, one experimental and one observational. The experiment consisted of monospecific plots of 17 plant species from which we collected bees over 3 years. The observational data consisted of bees collected from 66 species of plants growing in semi‐natural meadows, also over 3 years. Nineteen percent of the dominant crop‐pollinating species were regionally rare. Both rare species and crop‐pollinating species had strong preferences for certain plants, and the preferences of rare and crop‐pollinating bees were significantly but not strongly (r ≤ .54) correlated. Ten plant species were significantly preferred by both rare and crop‐pollinating bees. Synthesis and applications. We found several dominant crop pollinators that are rare at a regional scale, supporting the idea that rare species can be important providers of ecosystem services. The flower preferences of rare and crop‐pollinating bees are significantly positively associated, suggesting that plants chosen to support crop pollinators will benefit rare species as well. We identify plant species that are preferred by regionally rare bees and by crop pollinators, including 10 plant species preferred by both types of bees, and recommend these for use in pollinator habitat plantings.

Distribution of chemical residues in the beehive compartments and their transfer to the honeybee brood

Honeybee (Apis mellifera) is one of the most important crop and wild plant pollinators, playing an essential role in the agricultural production and the natural ecosystems. However, the number of honeybee colonies is decreasing alarmingly, which has motivated extensive research on the factors affecting their development and survival in some regions. Honeybees' exposure to pesticides and other chemicals has been identified as one of the causes of their decline. The present study evaluates the distribution of plant protection products, veterinary treatments and environmental contaminants inside the beehive, their persistence and their migration to the bee brood. During the five-month sampling period, only amitraz was applied to the colonies. Samples of beeswax, beebread (processed pollen) and bee brood were extracted and analyzed using GC-MS/MS and LC-MS/MS with a multiresidue method. The results showed the presence of 31 chemical residues in the samples. The highest concentrations of residues were detected in the beeswax and corresponded to amitraz (expressed as the sum of DMF and DMPF), coumaphos and tau-fluvalinate, with total concentrations of up to 16,858, 7102 and 1775 μg kg−1, respectively. These and other veterinary treatments were found to accumulate in the beeswax and migrate to other beehive matrices such as beebread and bee brood. Plant protection products used in agriculture were also found in the beehive matrices, especially in the beebread. Five different chemical residues (acrinathrin, amitraz, coumaphos, cypermethrin and tau-fluvalinate) were found in bee brood samples at concentration levels ranging from 1 to 167 μg kg−1. These findings reveal that bee brood reared in field conditions is in fact exposed to plant protection products and veterinary residues through direct contact with contaminated wax and via beebread although they had not been applied to the beehive.

Why Are Queens Broodless? Failed Nest Initiation Not Linked to Parasites, Mating Status, or Ovary Development in Two Bumble Bee Species of Pyrobombus (Hymenoptera: Apidae: Bombus).

Bumble bees (Bombus [Hymenoptera: Apidae]) are important pollinators for agricultural crops, which has led to their commercial domestication. Despite their importance, little is known about the reproductive biology of bumble bees native to North America. The Hunt bumble bee (Bombus huntii Greene [Hymenoptera: Apidae]) and the Vosnesensky bumble bee (Bombus vosnesenskii Radoszkowski [Hymenoptera: Apidae] are native candidates for commercial production in western North America due to their efficacy in providing commercial pollination services. Availability of pollinators native to the region in which services would be provided would minimize the likelihood of introducing exotic species and spreading novel disease. Some parasites are known to affect bumble bee reproduction, but little is known about their prevalence in North America or how they affect queen success. Only 38% of wild-caught B. huntii and 51% wild-caught B. vosnesenskii queens collected between 2015 and 2017 initiated nests in the laboratory. Our objective was to identify causal factors leading to a queen's inability to oviposit. To address this, we dissected each broodless queen and diagnosed diseases, assessed mating status, and characterized ovary development. Nematodes, arthropods, and microorganisms were detected in both species. Overall, 20% of queens were infected by parasites, with higher rates in B. vosnesenskii. Over 95% of both species were mated, and over 88% had developed ovaries. This suggests that parasitism and mating status were not primary causes of broodlessness. Although some failure to nest can be attributed to assessed factors, additional research is needed to fully understand the challenges presented by captive rearing.

Exposure of Larvae of the Solitary Bee Osmia bicornis to the Honey Bee Pathogen Nosema ceranae Affects Life History.

Wild bees are important pollinators of wild plants and agricultural crops and they are threatened by several environmental stressors including emerging pathogens. Honey bees have been suggested as a potential source of pathogen spillover. One prevalent pathogen that has recently emerged as a honey bee disease is the microsporidian Nosema ceranae. While the impacts of N. ceranae in honey bees are well documented, virtually nothing is known about its effects in solitary wild bees. The solitary mason bee Osmia bicornis is a common pollinator in orchards and amenable to commercial management. Here, we experimentally exposed larvae of O. bicornis to food contaminated with N. ceranae and document spore presence during larval development. We measured mortality, growth parameters, and timing of pupation in a semi-field experiment. Hatched individuals were assessed for physiological state including fat body mass, wing muscle mass, and body size. We recorded higher mortality in the viable-spore-exposed group but could only detect a low number of spores among the individuals of this treatment. Viable-spore-treated individuals with higher head capsule width had a delayed pupation start. No impact on the physiological status could be detected in hatched imagines. Although we did not find overt evidence of O. bicornis infection, our findings indicate that exposure of larvae to viable N. ceranae spores could affect bee development.

Analysis of miRNAs in the Heads of Different Castes of the Bumblebee Bombus lantschouensis (Hymenoptera: Apidae).

Bumblebees are important insect pollinators for many wildflowers and crops. MicroRNAs (miRNAs) are endogenous non-coding small RNAs that regulate different biological functions in insects. In this study, the miRNAs in the heads of the three castes of the bumblebee Bombus lantschouensis were identified and characterized by small RNA deep sequencing. The significant differences in the expression of miRNAs and their target genes were analyzed. The results showed that the length of the small RNA reads from males, queens, and workers was distributed between 18 and 30 nt, with a peak at 22 nt. A total of 364 known and 89 novel miRNAs were identified from the heads of the three castes. The eight miRNAs with the highest expressed levels in males, queens, and workers were identical, although the order of these miRNAs based on expression differed. The male vs. queen, male vs. worker, and worker vs. queen comparisons identified nine, fourteen, and four miRNAs with significant differences in expression, respectively. The different castes were clustered based on the differentially expressed miRNAs (DE miRNAs), and the expression levels of the DE miRNAs obtained by RT-qPCR were consistent with the read counts obtained through Solexa sequencing. The putative target genes of these DE miRNAs were enriched in 29 Gene Ontology (GO) terms, and catalytic activity was the most enriched GO term, as demonstrated by its association with 2837 target genes in the male vs. queen comparison, 3535 target genes in the male vs. worker comparison, and 2185 target genes in the worker vs. queen comparison. This study highlights the characteristics of the miRNAs in the three B. lantschouensis castes and will aid further studies on the functions of miRNAs in bumblebees.

Non-Bee Insects as Visitors and Pollinators of Crops: Biology, Ecology, and Management

Insects other than bees (i.e., non-bees) have been acknowledged as important crop pollinators, but our understanding of which crop plants they visit and how effective they are as crop pollinators is limited. To compare visitation and efficiency of crop-pollinating bees and non-bees at a global scale, we review the literature published from 1950 to 2018 concerning the visitors and pollinators of 105 global food crops that are known to benefit from animal pollinators. Of the 105 animal-pollinated crops, a significant proportion are visited by both bee and non-bee taxa (n = 82; 77%), with a total gross domestic product (GDP) value of US$780.8 billion. For crops with a narrower range of visitors, those that favor non-bees (n = 8) have a value of US$1.2 billion, compared to those that favor bees (n = 15), with a value of US$19.0 billion. Limited pollinator efficiency data were available for one or more taxa in only half of the crops (n = 61; 58%). Among the non-bees, some families were recorded visiting a wide range of crops (>12), including six families of flies (Syrphidae, Calliphoridae, Muscidae, Sarcophagidae, Tachinidae, and Bombyliidae), two beetle families (Coccinelidae and Nitidulidae), ants (Formicidae), wasps (Vespidae), and four families of moths and butterflies (Hesperiidae, Lycaenidae, Nymphalidae, and Pieridae). Among the non-bees, taxa within the dipteran families Syrphidae and Calliphoridae were the most common visitors to the most crops, but this may be an artifact of the limited data available. The diversity of species and life histories in these groups of lesser-known pollinators indicates that diet, larval requirements, and other reproductive needs will require alternative habitat management practices to bees.

Floral resources provided by the new energy crop, Silphium perfoliatum L. (Asteraceae)

Flower-visiting insects are important crop pollinators, but their populations in agricultural landscapes are declining. One reason is the decreasing quantity and quality of floral resources. Deterioration of the situation caused by an increasing production of energy crops like maize, a pollen-only resource, may be mitigated by alternative crops such as Silphium perfoliatum L., which produces pollen and nectar over a long-lasting flowering period (July–September). The aim of this study was to assess the floral resources of S. perfoliatum. We calculated pollen grains and nectar sugar mass per inflorescence as well as inflorescences per plant using experimental plots and commercial fields in Germany. In addition, we analyzed free and protein-bound amino acids in pollen as well as sugars and free amino acids in nectar. The amount of pollen and nectar sugar per inflorescence decreased with increasing stem branching. The production of pollen and nectar sugar, however, was greatest in the second half of August due to the high number of inflorescences per plant at that stage. About half of the farmers harvested S. perfoliatum before the end of flowering to gain higher methane yields. With an early harvest around the beginning of September about one sixth of total pollen and one fifth of total nectar sugar production were lost to pollinators. Pollen and nectar showed high amounts of certain essential amino acids, particularly histidine, but total amino acids were low in concentration. Hence, S. perfoliatum should be complemented with different bee fodder plants to ensure a well-balanced diet.

Seasonal shifts and complementary use of pollen sources by two bees, a lacewing and a ladybeetle species in European agricultural landscapes

Abstract Continuous availability of food resources, such as pollen, is vital for many insects that provide pollination and pest control services to agriculture. However, there is a lack of knowledge about the shared or complementary use of floral resources by such species, which hampers more effective landscape management to simultaneously promote them in agroecosystems. Here, we simultaneously quantified pollen use by a bumblebee (Bombus terrestris) and a mason bee (Osmia bicornis), two bee species recognized as important crop pollinators, as well as a lacewing (Chrysoperla carnea) and a ladybeetle species (Harmonia axyridis), both common predators of crop aphids, throughout the season in 23 agricultural landscapes in Germany and Switzerland. Pollen diets were more diverse and similar among C. carnea and H. axyridis compared to the two bee species, but all four species shared key pollen types early in the season such as Acer, Quercus, Salix and Prunus. All species exhibited a pronounced shift in pollen sources from primarily woody plants (mainly trees) in spring to primarily herbaceous plants in summer. The majority of pollen (overall ≥64%) came from non‐agricultural plants even in crop‐dominated landscapes. Synthesis and applications. Our results highlight the importance of trees as pollen sources for many insect species, particularly early in the season. Our findings support incentives that promote heterogeneous agricultural landscapes including both woody and herbaceous semi‐natural habitats, ensuring phenological complementarity of floral resources for insect species that can provide pollination and pest control services to agriculture. The identified key plant species can help to design and optimize agri‐environment schemes to promote these functionally important insects.

Impact of nutritional stress on the honeybee colony health

Honeybees Apis mellifera are important pollinators of wild plants and commercial crops. For more than a decade, high percentages of honeybee colony losses have been reported worldwide. Nutritional stress due to habitat depletion, infection by different pests and pathogens and pesticide exposure has been proposed as the major causes. In this study we analyzed how nutritional stress affects colony strength and health. Two groups of colonies were set in a Eucalyptus grandis plantation at the beginning of the flowering period (autumn), replicating a natural scenario with a nutritionally poor food source. While both groups of colonies had access to the pollen available in this plantation, one was supplemented with a polyfloral pollen patty during the entire flowering period. In the short-term, colonies under nutritional stress (which consumed mainly E. grandis pollen) showed higher infection level with Nosema spp. and lower brood and adult bee population, compared to supplemented colonies. On the other hand, these supplemented colonies showed higher infection level with RNA viruses although infection levels were low compared to countries were viral infections have negative impacts. Nutritional stress also had long-term colony effects, because bee population did not recover in spring, as in supplemented colonies did. In conclusion, nutritional stress and Nosema spp. infection had a severe impact on colony strength with consequences in both short and long-term.