Dominance of Fructose-Associated Fructobacillus in the Gut Microbiome of Bumblebees (Bombus terrestris) Inhabiting Natural Forest Meadows

Bumblebees are key pollinators in agricultural landscapes. However, little is known about how gut microbial communities respond to anthropogenic changes. We used commercially produced colonies of buff-tailed bumblebees (Bombus terrestris) placed in three habitats. Whole guts (midgut, hindgut, and rectum) of B. terrestris specimens were dissected from the body and analyzed using 16S phylogenetic community analysis. We observed significantly different bacterial community composition between the agricultural landscapes (apple orchards and oilseed rape (Brassica napus) fields) and forest meadows, whereas differences in gut communities between the orchards and oilseed rape fields were nonsignificant. Bee-specific bacterial genera such as Lactobacillus, Snodgrassella, and Gilliamella dominated gut communities of B. terrestris specimens. In contrast, the guts of B. terrestris from forest meadows were dominated by fructose-associated Fructobacillus spp. Bacterial communities of workers were the most diverse. At the same time, those of males and young queens were less diverse, possibly reflecting greater exposure to the colony’s inner environment compared to the environment outside the colony, as well as bumblebee age. Our results suggest that habitat quality, exposure to environmental microbes, nectar quality and accessibility, and land use significantly affect gut bacterial composition in B. terrestris.

Substantial variability in morphological scaling among bumblebee colonies

Differences in organ scaling among individuals may play an important role in determining behavioural variation. In social insects, there are well-documented intraspecific differences in colony behaviour, but the extent that organ scaling differs within and between colonies remains unclear. Using 12 different colonies of the bumblebee Bombus terrestris , we aim to address this knowledge gap by measuring the scaling relationships between three different organs (compound eyes, wings and antennae) and body size in workers . Though colonies were exposed to different rearing temperatures, this environmental variability did not explain the differences of the scaling relationships. Two colonies had differences in wing versus antenna slopes, three colonies showed differences in wing versus eye slopes and a single colony has differences between eye versus antenna slopes. There are also differences in antennae scaling slopes between three different colonies, and we present evidence for putative trade-offs in morphological investment. We discuss the utility of having variable scaling among colonies and the implication for understanding variability in colony fitness and behaviour.

Higher developmental temperature increases queen production and decreases worker body size in the bumblebee Bombus terrestris

Climate change and increasing average temperatures are now affecting most ecosystems. Social insects such as bumblebees are especially impacted because these changes create spatial, temporal and morphological mismatches that could impede their ability to find food resources and mate. However, few studies have assessed how the colony and life cycle are affected when temperatures rise above optimal rearing temperature. It has become imperative to understand how heat stress affects the life history traits of insect pollinators as well as how changes in life history interact with other traits like morphology. For example, a decrease in the number of foraging workers could be balanced by producing larger workers, able to forage at longer distances and gather more resources. Here, we investigated the impact of temperature on colony production and body size in the bumblebee Bombus terrestris. Colonies were exposed to two temperatures: 25 °C, which is around the optimal temperature for larval development and 33 °C, which is slightly above the set-point that is considered stressful for bumblebees. Although the production of males and workers wasn’t significantly affected by these different temperatures, queen production and reproductive investment were much higher for colonies placed in 33 °C than in 25 °C. We also found that, in agreement with the temperature-size rule, workers were significantly smaller in the higher temperature. The decrease in worker body size could affect resource collection and pollination if their foraging distance and the quantity of food they are taking back to the colony decreases. While in our controlled conditions the bumblebees were fed ad libitum, the decrease of resource collection in field conditions could prevent colonies from producing as many queens as in our study. Together with the decrease of worker body size, our results suggest that elevated temperatures could ultimately have a negative impact on bumblebee colony fitness. Indeed, smaller workers are known to have weaker flight performance which could affect foraging performance and consequently colony development.

Aspectos de la fisiología y el cultivo del lulo (Solanum quitoense LAM.) en Colombia: una revisión

Contextualización: el lulo es un fruto promisorio de alta demanda en los mercados, debido a sus excelentes propiedades organolépticas, además de ser fuente importante de vitaminas y minerales. Vacío de conocimiento: en los últimos diez años se han desarrollado múltiples investigaciones sobre la ecofisiología de la planta de lulo, sin que exista una revisión de literatura de este. Propósito del estudio: recopilar aspectos generales del cultivo, incluyendo los principales requerimientos agronómicos y aspectos ecofisiológicos para una producción sustentable. Metodología: la investigación se basó en una revisión metódica y ordenada de los estudios más relevantes publicados en diferentes bases de datos. Resultados y conclusiones: el cultivo de lulo se cultiva entre los 1900 y 2200 msnm en Colombia, con temperaturas de 15 a 24 °C. Requiere entre 1.500 a 2.500 mm de precipitación al año. Se asemeja a una planta de días cortos, que exhibe su mejor desarrollo en sitios sombreados con humedades relativas cercanas al 80 %. El método más eficiente de polinización es el realizado por abejorros (Bombus terrestris y Bombus sp.) por medio de vibraciones. La fotosíntesis neta del cultivo de lulo varia de 5,52 a 34,03 μmol CO2 m-2 s-1 a los 398 y 460 días después de transplante; mientras que la eficiencia máxima del fotosistema II (Fv/Fm) en el cultivo oscila entre 0,55 y 0,65, para plantas sin y con aplicación de nitrógeno foliar. Los valores de clorofila (a, b y total) para plantas de lulo son mayores en plantas en etapa de trasplante que en producción, debido a la reducida área fotosintética. Las concentraciones de nitrógeno mayores a 110 mg L-1 generan mejor rendimiento y mayor área foliar. La planta de lulo comienza la producción entre los ocho y 12 meses después ser trasplantada y produce rendimientos promedio de 8,5 t ha-1. El desarrollo y crecimiento de los frutos de lulo tiene un comportamiento que se ajusta a un modelo logístico sigmoide simple. Los frutos de lulo en la cosecha pueden llegar a alcanzar hasta 209 g con una firmeza de 58 N y valores de 13.6 °Brix y 56,2, 10,8 y 46,8 para los parámetros de color luminosidad (L*), cromaticidad a* y cromaticidad b*, respectivamente.

Parent of origin DNA methylation as a potential mechanism for genomic imprinting in bees.

Genomic imprinting is defined as parent-of-origin allele-specific expression. In order for genes to be expressed in this manner an `imprinting' mark must be present to distinguish the parental alleles within the genome. In mammals imprinted genes are primarily associated with DNA methylation. Genes exhibiting parent-of-origin expression have recently been identified in two species of Hymenoptera with functional DNA methylation systems; Apis mellifera and Bombus terrestris. We carried out whole genome bisulfite sequencing of parents and offspring from reciprocal crosses of two B. terrestris subspecies in order to identify parent-of-origin DNA methylation. We were unable to survey a large enough proportion of the genome to draw a conclusion on the presence of parent-of-origin DNA methylation however we were able to characterise the sex- and caste-specific methylomes of B. terrestris for the first time. We find males differ significantly to the two female castes, with differentially methylated genes involved in many histone modification related processes. We also analysed previously generated honeybee whole genome bisulfite data to see if genes previously identified as showing parent-of-origin DNA methylation in the honeybee show consistent allele-specific methylation in independent data sets. We have identified a core set of 12 genes in female castes which may be used for future experimental manipulation to explore the functional role of parent-of-origin DNA methylation in the honeybee. Finally, we have also identified allele-specific DNA methylation in honeybee male thorax tissue which suggests a role for DNA methylation in ploidy compensation in this species.

Assessing the Toxicological Interaction Effects of Imidacloprid, Thiamethoxam, and Chlorpyrifos on Bombus Terrestris Based on the Combination Index

In modern agricultural production, a variety of pesticides are widely used to protect crops against pests. However, extensive residues of these pesticides in the soil, water, and pollen have negatively affected the health of nontarget organisms, especially among pollinators such as bumblebees. As an important pollinator, the bumblebee plays a vital role in agricultural production and the maintenance of ecosystem diversity. Previous research has focused on the effects of a single pesticide on pollinating insects; however, the synergistic effects of multiple agents on bumblebees have been not studied in detail. In our test, the individual and combined toxicities of chlorpyrifos, thiamethoxam, and imidacloprid to bumblebees after 48 h of oral administration were documented by the equivalent linear equation method. Our results showed that the toxicity of each single pesticide exposure, from high to low, was imidacloprid, thiamethoxam, and chlorpyrifos. All binary and ternary combinations showed synergistic or additive effects. Therefore, our research not only shows that the mixed toxicity of insecticides has a significant effect on bumblebees, but also provides scientific guidelines for assessing the safety risks to bumblebees of these three insecticide compounds. In assessing the risk to pollinating insects, the toxicity levels of laboratory experiments are much lower than the actual toxicity in the field.

Genetic Relationships Between Commercially Produced and Natural Populations of Bombus Terrestris Dalmatinus in Terms of Mitochondrial COI and CytB

Bombus terrestris dalmatinus is naturally common in many countries, including Turkey, and is also used commercially for the pollination of greenhouse plants. Intensive commercial production and international trade in many countries are considered as reasons for the disappearance of some natural populations. Hybridization of native bumble bees with those produced commercially, but having escaped from greenhouses and colonization of these commercial bees in natural habitats are cause for concern. In order to assess this concern, B. t. dalmatinus workers were collected from twelve different populations: five commercial producers, three surrounding greenhouse centers, three natural areas at least 30 km away from greenhouses, and one more recent greenhouse zone in Antalya, Turkey. The genetic variations and relationships among the twelve populations were estimated using SNP haplotypes determined in mitochondrial COI and CytB. Twenty and sixteen haplotypes were obtained for COI and CytB, respectively. A single haplotype, H1, was widespread with a high frequency in all individuals for both genes. Individuals collected from around greenhouse centers and commercial companies had more common haplotypes. The genetic variations of intra-populations were higher than the interpopulations in both COI (65.41%>34.59%) and CytB (72.47%>27.53%). The natural and commercial populations were genetically more distant from each other considering Fst values. However, samples from near the greenhouses had a higher similarity with the commercially produced samples, while the natural populations far away from greenhouses still retained their genetic distinctiveness.

Pollen Source Richness May Be a Poor Predictor of Bumblebee (Bombus terrestris) Colony Growth

Agricultural intensification has drastically altered foraging landscapes for bees, with large-scale crop monocultures associated with floral diversity loss. Research on bumblebees and honeybees has shown individuals feeding on pollen from a low richness of floral sources can experience negative impacts on health and longevity relative to higher pollen source richness of similar protein concentrations. Florally rich landscapes are thus generally assumed to better support social bees. Yet, little is known about whether the effects of reduced pollen source richness can be mitigated by feeding on pollen with higher crude protein concentration, and importantly how variation in diet affects whole colony growth, rearing decisions and sexual production. Studying queen-right bumblebee (Bombus terrestris) colonies, we monitored colony development under a polyfloral pollen diet or a monofloral pollen diet with 1.5–1.8 times higher crude protein concentration. Over 6 weeks, we found monofloral colonies performed better for all measures, with no apparent long-term effects on colony mass or worker production, and a higher number of pupae in monofloral colonies at the end of the experiment. Unexpectedly, polyfloral colonies showed higher mortality, and little evidence of any strategy to counteract the effects of reduced protein; with fewer and lower mass workers being reared, and males showing a similar trend. Our findings (i) provide well-needed daily growth dynamics of queenright colonies under varied diets, and (ii) support the view that pollen protein content in the foraging landscape rather than floral species richness per se is likely a key driver of colony health and success.

Acute Imidacloprid Exposure Alters Mitochondrial Function in Bumblebee Flight Muscle and Brain

Mitochondria are intracellular organelles responsible for cellular respiration with one of their major roles in the production of energy in the form of ATP. Activities with increased energetic demand are especially dependent on efficient ATP production, hence sufficient mitochondrial function is fundamental. In bees, flight muscle and the brain have particularly high densities of mitochondria to facilitate the substantial ATP production required for flight activity and neuronal signalling. Neonicotinoids are systemic synthetic insecticides that are widely utilised against crop herbivores but have been reported to cause, by unknown mechanisms, mitochondrial dysfunction, decreasing cognitive function and flight activity among pollinating bees. Here we explore, using high-resolution respirometry, how the neonicotinoid imidacloprid may affect oxidative phosphorylation in the brain and flight muscle of the buff-tailed bumblebee, Bombus terrestris. We find that acute exposure increases routine oxygen consumption in the flight muscle of worker bees. This provides a candidate explanation for prior reports of early declines in flight activity following acute exposure. We further find that imidacloprid increases the maximum electron transport capacity in the brain, with a trend towards increased overall oxygen consumption. However, intra-individual variability is high, limiting the extent to which apparent effects of imidacloprid on brain mitochondria are shown conclusively. Overall, our results highlight the necessity to examine tissue-specific effects of imidacloprid on respiration and energy production.

Genetic diversity among queen bee, worker bees and larvae in terms of retrotransposon movements

Objective Honeybee (Apis mellifera L.) is a model organism, contributing significant effect on global ecology by pollination and examining due to its social behaviour. Methods In this study, barley-specific Sukkula and Nikita retrotransposons were analysed using IRAP (Inter-Retrotransposon Amplification Polymorphism) marker technique, and the relationships between retrotransposon movements and development were also investigated in three different colonies of the Caucasian bee (Apis mellifera caucasica). Furthermore, transposon sequences belonging to Apis mellifera, Bombus terrestris, Triticum turgidum and Hordeum vulgare were also examined to figure out evolutionary relationships. Results For this purpose, a queen bee, five worker bees, and five larvae from each colony were studied. Both retrotransposons were found in all samples in three colonies with different polymorphism ratios (0-100% for Nikita and 0-67% for Sukkula). We also determined polymorphisms in queen-worker (0-83% for Nikita, 0-63% for Sukkula), queen-larvae (0-83% for Nikita, 0-43% for Sukkula) and worker-larvae comparisons (0-100% for Nikita, 0-63% for Sukkula) in colonies. Moreover, close relationships among transposons found in plant and insect genomes as a result of in silico evaluations to verify experimental results. Conclusion This work could be one of the first studies to analyse plant-specific retrotransposons’ movements in honeybee genome. Results are expected to understand evolutionary relationships in terms of horizontal transfer of transposons among kingdoms.