Bees are vital for a healthy and functioning planet, ensuring food security and preserving biodiversity. These essential pollinators directly and indirectly support several of the United Nation's Sustainable Development Goals, from "SDG 2: Zero Hunger" to "SDG 15: Life on Land". However, largely due to human activities, bee populations are declining worldwide. Almost 35% of invertebrate pollinators, including many bee species are facing extinction. Recognising their importance, the United Nations has designated May the 20th as World Bee Day, urging everyone to help protect bees. In response to the call to raise awareness, we highlight research from across the BMC Series.

BMC Ecology and Evolution - Oral exposure to thiacloprid-based pesticide (Calypso SC480) causes physical poisoning symptoms and impairs the cognitive abilities of bumble bees

The insecticide Calypso SC480, which contains the active substance thiacloprid, is used on crops to control insect pests. However, it can be lethal to bees at high concentrations. The European Union (EU) has conducted risk assessments to evaluate the toxicity of insecticides, focusing on the exposure level at which half of the tested bees die. This has led to the development of EU guidelines for pesticide use. However, there has been a lack of research on the sub-lethal effects of lower exposure levels on bees. Lotta Kaila, a doctoral researcher at the University of Helsinki, conducted a study published in BMC Ecology and Evolution to investigate the impact of thiacloprid concentrations used in Finnish agriculture on the learning and memory abilities of bumblebees.

Learning performance and memory were tested in a ten-colour test in which a bumblebee had to learn to identify the five colours that rewarded it with sugar water. Oral exposure to thiacloprid residues equivalent to concentrations found in honeybee collected pollen and nectar from Finnish fields where thiacloprid was used according to commercial pesticide instructions impaired the bees' learning performance compared to untreated controls.

The study shows that even small doses of pesticides, which are considered less harmful, can still impact the learning ability of bumblebees and potentially weaken their populations over time. Therefore, it's not enough to only look at lethal doses when studying the effects of pesticides on pollinating insects. Sub-lethal doses can also affect the ability of pollinators to find food, which may weaken populations long term. These findings emphasize the need for a better understanding of pesticide residues in the environment and their impact on pollinators. This information can help the scientific community and policymakers improve the sustainable use of pesticides.

BMC Plant Biology - Global warming impairs the olfactory floral signaling in strawberry

Changes in the scent of flowers, such as those induced by global warming, can impact how appealing plants are to pollinators. Bees rely on their antennae's odour sensors to decipher volatile signals released by flowers, helping them locate flowers and assess the quality of their pollen and nectar. A study conducted by Guaraci Duran Cordeiro and Stefan Dötterl from the University of Salzburg, published in BMC Plant Biology, explores whether changes in the floral scent of strawberry plants due to temperature shifts impacts their attractiveness to bee pollinators.

The researchers used gas chromatography to analyse volatile organic compounds in scent samples and electroantennography to measure the detection of volatiles perceived by the antennal olfactory apparatus of bees to test whether temperature-induced shifts in the floral scent of strawberries affect their attractiveness to bees (Apis mellifera, Bombus terrestris, Osmia bicornis). They found that strawberry flowers grown under optimum temperatures (mean 20 °C) released 10.4 ng/flower/hour of scent compounds. However, the flowers did not emit any detectable scent in warmer conditions (mean 25 °C). In behavioural experiments, the bees were attracted by the scents emitted under the optimum temperature scenario.

The findings suggest that changes in floral scent emissions due to global warming could potentially impact pollination, adversely affecting ecosystem functioning and crop productivity. The study highlights the need for further research into the influence of temperature-induced changes in floral scent on plant-pollinator chemical communication.

BMC Genomics - Differential bumble bee gene expression associated with pathogen infection and pollen diet

The gut parasite, Crithidia bombi, is commonly found in the bumblebee species Bombus impatiens. This protozoan pathogen is spread among colonies through flowers and is prevalent in Europe, Australasia, and the Americas. While benign in favourable conditions, Crithidia bombi can significantly affect bumblebee health, including reduced colony reproduction and fitness, impaired cognitive abilities, and altered foraging behaviour when combined with other stressors. Recent studies have shown that consuming sunflower pollen (Helianthus annuus) can lessen the severity of the pathogen in Bombus impatiens. However, the specific mechanisms underlying this therapeutic effect are not fully understood.

To help elucidate the medicinal effect, the authors of a study in BMC Genomics analysed the transcriptomes of bumble bee workers to understand the physiological response to sunflower pollen consumption and Crithidia bombi infection. Workers were exposed to parasite cells or control and were fed either sunflower or wildflower pollen. The gene expression profiles from their entire abdomens were then sequenced using Illumina NextSeq 500 technology.

Sequencing data analysis found that sunflower pollen boosts the expression of genes expressed by immune cells, such as serine proteases and Toll receptors, as well as the transcript encoding the anti-microbial peptide hymenopteran in Crithidia bombi infected bees. Additionally, sunflower pollen upregulates genes associated with detoxification and the maintenance of gut health in both infected and uninfected bees. Further research into understanding host responses that drive the medicinal effect of sunflower pollen in bumble bees may open new avenues for managing bee pathogens.

BMC Research Notes - The first ITS2 sequence data set of eDNA from honey of Malaysian giant honeybees (Apis dorsata) and stingless bees (Heterotrigona itama) reveals plant species diversity

Bees gather genetic traces of many organisms belonging to the same community while visiting flowers to collect honey. The authors of a study in BMC Research Notes have generated sequencing datasets to analyze the environmental DNA (eDNA) found in honey collected by two native Malaysian bee species, Apis dorsata and Heterotrigona itama. The datasets provide valuable insights into the plant species visited by these bees, shedding light on important plant-pollinator interactions within Malaysian forests. Additionally, investigators can use the datasets to determine the geographical and botanical origins of the honey.  

Fueled by recent technological advances, researchers are beginning to unlock genetic information in honey for various uses. Using honey as a source of eDNA can help evaluate community composition and answer many questions regarding biotic interactions within ecosystems. For example, eDNA datasets from honey or pollen found on the body of pollinators can help determine plant-pollinator interactions, monitor bee and plant health and detect pathogens and parasites. Such data is also helpful in ascertaining the geographical origin of honey to combat food fraud.

Call for papers!

If you're interested in learning more about pollinators, explore the following BMC Series article collections that are currently open for submissions:

• Ecology and evolution of plant–pollinator interactions at BMC Ecology and Evolution
• Genomics of social insects at BMC Genomics