Gut microbiome helps honeybee (Apis mellifera) resist the stress of toxic nectar plant (Bidens pilosa) exposure: Evidence for survival and immunity.

Honeybee (Apis mellifera) ingestion of toxic nectar plants can threaten their health and survival. However, little is known about how to help honeybees mitigate the effects of toxic nectar plant poisoning. We exposed honeybees to different concentrations of Bidens pilosa flower extracts and found that B. pilosa exposure significantly reduced honeybee survival in a dose-dependent manner. By measuring changes in detoxification and antioxidant enzymes and the gut microbiome, we found that superoxide dismutase, glutathione-S-transferase and carboxylesterase activities were significantly activated with increasing concentrations of B. pilosa and that different concentrations of B. pilosa exposure changed the structure of the honeybee gut microbiome, causing a significant reduction in the abundance of Bartonella (p < 0.001) and an increase in Lactobacillus. Importantly, by using Germ-Free bees, we found that colonization by the gut microbes Bartonella apis and Apilactobacillus kunkeei (original classification as Lactobacillus kunkeei) significantly increased the resistance of honeybees to B. pilosa and significantly upregulated bee-associated immune genes. These results suggest that honeybee detoxification systems possess a level of resistance to the toxic nectar plant B. pilosa and that the gut microbes B. apis and A. kunkeei may augment resistance to B. pilosa stress by improving host immunity.

Caffeine Consumption Helps Honey Bees Fight a Bacterial Pathogen.

Caffeine has long been used as a stimulant by humans. Although this secondary metabolite is produced by some plants as a mechanism of defense against herbivores, beneficial or detrimental effects of such consumption are usually associated with dose. The Western honey bee, Apis mellifera, can also be exposed to caffeine when foraging at Coffea and Citrus plants, and low doses as are found in the nectar of these plants seem to boost memory learning and ameliorate parasite infection in bees. In this study, we investigated the effects of caffeine consumption on the gut microbiota of honey bees and on susceptibility to bacterial infection. We performed in vivo experiments in which honey bees, deprived of or colonized with their native microbiota, were exposed to nectar-relevant concentrations of caffeine for a week, then challenged with the bacterial pathogen Serratia marcescens. We found that caffeine consumption did not impact the gut microbiota or survival rates of honey bees. Moreover, microbiota-colonized bees exposed to caffeine were more resistant to infection and exhibited increased survival rates compared to microbiota-colonized or microbiota-deprived bees only exposed to the pathogen. Our findings point to an additional benefit of caffeine consumption in honey bee health by protecting against bacterial infections. IMPORTANCE The consumption of caffeine is a remarkable feature of the human diet. Common drinks, such as coffee and tea, contain caffeine as a stimulant. Interestingly, honey bees also seem to like caffeine. They are usually attracted to the low concentrations of caffeine found in nectar and pollen of Coffea plants, and consumption improves learning and memory retention, as well as protects against viruses and fungal parasites. In this study, we expanded these findings by demonstrating that caffeine can improve survival rates of honey bees infected with Serratia marcescens, a bacterial pathogen known to cause sepsis in animals. However, this beneficial effect was only observed when bees were colonized with their native gut microbiota, and caffeine seemed not to directly affect the gut microbiota or survival rates of bees. Our findings suggest a potential synergism between caffeine and gut microbial communities in protection against bacterial pathogens.

Floral tea polyphenols can improve honey bee memory retention and olfactory sensitivity.

Animal-pollinated plants face a common problem, how their defensive anti-herbivore compounds may impair or alter pollinator behavior. Evolution has tailored multiple solutions, which largely involve pollinator tolerance or manipulation, to the benefit of the plant, not the removal of these compounds from pollen or nectar. The tea plant, Camilla sinensis, is famous for the caffeine and tea polyphenols (TP) that it produces in its leaves. However, these compounds are also found in its nectar, which honey bees readily collect. We examined the effects of these compounds on bee foraging choices, learning, memory, and olfactory sensitivity. Foragers preferred a sucrose feeder with 100 µg or 10 µg TP/ml over a control feeder. Caffeine, but not TP, weakly increased honey bee learning. Both caffeine and TP significantly increased memory retention, even when tested 7 d after the last learning trial. In addition, TP generally elevated EAG responsiveness to alarm pheromone odors. These results demonstrate that other secondary plant compounds, not only caffeine, can attract pollinators and influence their learning and memory.

Pollination in a new climate: Assessing the potential influence of flower temperature variation on insect pollinator behaviour.

Climate change has the potential to enhance or disrupt biological systems, but currently, little is known about how organism plasticity may facilitate adaptation to localised climate variation. The bee-flower relationship is an exemplar signal-receiver system that may provide important insights into the complexity of ecological interactions in situations like this. For example, several studies on bee temperature preferences show that bees prefer to collect warm nectar from flowers at low ambient temperatures, but switch their preferences to cooler flowers at ambient temperatures above about 30° C. We used temperature sensor thermal probes to measure the temperature of outdoor flowers of 30 plant species in the Southern regions of the Australian mainland, to understand how different species could modulate petal temperature in response to changes in ambient temperature and, potentially, influence the decision-making of bees in the flowering plant's favour. We found that flower petal temperatures respond in different ways to changing ambient temperature: linearly increasing or decreasing relative to the ambient temperature, dynamically changing in a non-linear manner, or varying their temperature along with the ambient conditions. For example, our investigation of the difference between ambient temperature and petal temperature (ΔT), and ambient temperature, revealed a non-linear relationship for Erysimum linifolium and Polygala grandiflora that seems suited to bee temperature preferences. The temperature profiles of species like Hibertia vestita and H. obtusifolia appear to indicate that they do not have a cooling mechanism. These species may therefore be less attractive to bee pollinators in changing climatic conditions with ambient temperatures increasingly above 30° C. This may be to the species' detriment when insect-pollinator mediated selection is considered. However, we found no evidence that flower visual characteristics used by bees to identify flowers at close range, such as colour or shape, were straightforward modulators of floral temperature. We could not identify any clear link to phylogenetic history and temperature modulation either. Mapping our test flower distribution on the Australian continent however, indicates a potential clustering that suggests different flower responses may constitute adaptations to local conditions. Our study proposes a framework for modelling the potential effects of climate change and floral temperature on flower pollination dynamics at local and global scales.

[Sugar-Supplemented Substrates Contaminated by Agricultural Inputs Favor the Proliferation of Aedes albopictus (Diptera: Culicidae)]. / Les substrats sucrés contaminés par les intrants agricoles favorisent la prolifération du moustique Aedes albopictus (Diptera : Culicidae).

Originating from South-East Asian tropical forests, Aedes albopictus (Skuse) (Diptera: Culicidae) is a mosquito of great genetic plasticity, which allowed it to adapt to a large variety of environments including the urban ones. Yet many a city nowadays comprises peri urban zones close to land devoted to farming. The sites where Ae. albopictus live and reproduce, located on the fringe of nectarfilled blossoming crops (orchards, colza and sunflower fields) are often polluted by chemical inputs such as fertilizers and pesticides. In this laboratory study we have assessed the impact of sugar-supplemented solutions contaminated by NPK fertilizer and/or by diflubenzuron or pyriproxyfen insecticides on adults of Ae. albopictus mosquitoes. The results have shown that the females feeding on a sweetened solution containing NPK fertilizer laid a significantly greater number of eggs. However when the sweetened solutions contained diflubenzuron or pyriproxyfen insecticides, the actions of both combinations resulted in a noticeable reduction of the numbers of eggs laid and the ones hatching. Finally when the sweetened solutions had been jointly polluted by the fertilizer and either one of the larvicides, the sterilizing effect of the insecticides was completely obliterated regarding both the numbers of eggs laid and the ones hatching. We are led to conclude that the somewhat inconsistent use of pesticides and fertilizers in agriculture bring about new ecological systems favorable to the proliferation of mosquitoes.

Originaire des forêts tropicales d'Asie du Sud-Est, Aedes albopictus (Skuse) (Diptera : Culicidae) est un moustique doté d'une grande plasticité génétique qui lui a permis de s'adapter à des environnements très divers, dont les milieux urbains. Or nombreuses sont les villes aujourd'hui où les quartiers périurbains s'installent à proximité de territoires ruraux à vocation agricole. Lorsque les lieux de vie et de reproduction d'Ae. albopictus se situent en lisière de cultures dont les fleurs sont riches en nectar (à l'exemple des arbres fruitiers, du colza et du tournesol), les adultes mâles et femelles se nourrissent d'exsudats sucrés souvent souillés par des intrants chimiques (engrais et pesticides). Nous avons mesuré dans cette étude de laboratoire, les impacts que généraient des solutions sucrées contaminées par un engrais NPK et/ou par les insecticides diflubenzuron et pyriproxyfen. Les résultats révèlent que lorsque les adultes d'Ae. albopictus absorbent une solution sucrée contenant un engrais NPK, les nombres d'oeufs pondus par les femelles s'en trouvent significativement augmentés. Quand une solution sucrée est au contraire contaminée par les insecticides diflubenzuron ou pyriproxyfen, l'action des deux composés provoque une nette diminution des nombres d'oeufs pondus mais aussi de ceux qui éclosent. Enfin, lorsque les réserves en sucre sont polluées à la fois par l'engrais et l'un ou l'autre des deux larvicides, l'effet stérilisant induit par les deux insecticides disparaît totalement, tant au niveau des nombres d'oeufs pondus que des nombres d'oeufs qui éclosent. Ces observations nous enseignent que l'utilisation pas toujours raisonnée des pesticides et des engrais en agriculture crée des situations écologiques nouvelles, favorables à la pullulation des moustiques.

Dual Effect of Phenolic Nectar on Three Floral Visitors of Elsholtzia rugulosa (Lamiaceae) in SW China.

Some plants secrete toxic nectar to appeal to most effective pollinators and deter non-pollinators or nectar thieves; however available information about ecological function of toxic nectar remains scarce. Elsholtzia rugulosa stands out as a plant with toxic nectar recorded in SW China. We focused on the functional significance of the phenolic compound that imparts toxic to the nectar of E. rugulosa. The effects of phenolic nectar were studied in three visitors of the flowers of the winter-blooming E. rugulosa Hemsl. (Lamiaceae) in SW China. The pollinating species Apis cerana Fabricius (Apidae; Asian honey bee) and two occasional visitors, Vespa velutina Lepeletier (Vespidae; yellow-legged Asian hornet) and Bombus eximius Smith (Apidae; a bumble bee) were tested for their preferences for low and high concentrations of 4-hydroxybenzoic acid in hexose and sucrose solutions. The pollinator is important for the plant, which is dependent on pollinator visits to attain a higher seed production and it is most likely that the combination of phenolic toxic nectar and the adaptation to phenolic nectar by A. cerana delivers an evolutionary advantage to both actors. The low and high concentrations of the phenolic acid were nearly totally refused by both occasional visitors V. velutina and B. eximius and were preferred by the pollinator A. cerana. E. rugulosa gains by having a much higher seed production and the pollinating honey bee by having an exclusive and reliable food source during the winter season at high altitudes in SW China. We found that the function of the toxic phenolic compound has dual roles by appealing to legitimate pollinators and deterring non-pollinators of E. rugulosa.

[Placebo and pediatric cough: the constant reinvention of the wheel]. / Placebo e tosse pediatrica: la riscoperta incessante dell'acqua calda.

The placebo effect has been studied and discussed in depth in recent years but, despite the extensive literature on the subject, the evidence of its impact in the clinic still arouses surprise. A study published in a major international journal of Pediatrics has compared blue agave pasteurized nectar, placebo and no treatment. The results demonstrate the greater effectiveness of both blue agave nectar and placebo versus the no-therapy option. Nothing new under the sun, except for a forced reflection on the real need of clinical research on the subject.

Effects of agave nectar versus sucrose on weight gain, adiposity, blood glucose, insulin, and lipid responses in mice.

Agave nectar is a fructose-rich liquid sweetener derived from a plant, and is often promoted as a low glycemic alternative to refined sugar. However, little scientific research has been conducted in animals or humans to determine its metabolic and/or health effects. The aim of this study was to explore the influence of agave nectar versus sucrose on weight gain, adiposity, fasting plasma blood glucose, insulin, and lipid levels. Eighteen (n=18) male ICR mice (33.8±1.6 g) were divided into two groups (n=6 for agave nectar and n=12 for sucrose) and provided free access to one of two diets of equal energy densities differing only in a portion of the carbohydrate provided. Diets contained 20% carbohydrate (by weight of total diet) from either raw agave nectar or sucrose. Epididymal fat pads were excised, and blood was collected after 34 days. Weight gain (4.3±2.2 vs. 8.4±3.4 g), fat pad weights (0.95±0.54 vs. 1.75±0.66 g), plasma glucose (77.8±12.2 vs. 111.0±27.9 mg/dL), and insulin (0.61±0.29 vs. 1.46±0.81 ng/mL) were significantly lower (P≤.05) for agave nectar-fed mice compared to sucrose-fed mice respectively. No statistically significant differences in total cholesterol or triglycerides were detected. These results suggest that in comparison to sucrose, agave nectar may have a positive influence on weight gain and glucose control. However, more research with a larger sample of animals and/or with human subjects is warranted.

Evaluation of antioxidant and mutagenic activities of honey-sweetened cashew apple nectar.

In vitro chemical properties and antioxidant potential and in vivo mutagenic activity of honey-sweetened cashew apple nectar (HSCAN), a beverage produced from the cashew pseudo-fruit (Anacardium occidentale L.) and of its constituents were assessed. Analytical procedures were carried out to investigate the honey used in the HSCAN preparation, and the results observed are in accordance with Brazilian legal regulations, except for diastase number. HSCAN and pulp were investigated for ascorbic acid, carotenoid, anthocyanin and total phenolic contents, and both showed high acid ascorbic concentrations. Antioxidant capacity using 2,2-diphenyl-1-picrylhydrazyl radical (DPPH) and/or ß-carotene/linoleic acid systems were applied and demonstrated a weak antioxidant capacity of honey and HSCAN, but cashew apple pulp demonstrated high antioxidant capacity. A weakly positive mutagenic effect of cashew pulp 20% was observed using the somatic mutation and recombination test (SMART) in Drosophila melanogaster only in the high-bioactivation (HB) cross. On the contrary, HSCAN was not mutagenic in both standard and high bioactivation crosses. HSCAN exhibited slight antioxidant activity, which could be associated with the high amount of ascorbic acid found in the samples evaluated. The beverage prepared did not induce DNA damage in somatic cells of D. melanogaster, which means that it is neither mutagenic nor recombinagenic in this test system.

Nectar theft and floral ant-repellence: a link between nectar volume and ant-repellent traits?

As flower visitors, ants rarely benefit a plant. They are poor pollinators, and can also disrupt pollination by deterring other flower visitors, or by stealing nectar. Some plant species therefore possess floral ant-repelling traits. But why do particular species have such traits when others do not? In a dry forest in Costa Rica, of 49 plant species around a third were ant-repellent at very close proximity to a common generalist ant species, usually via repellent pollen. Repellence was positively correlated with the presence of large nectar volumes. Repellent traits affected ant species differently, some influencing the behaviour of just a few species and others producing more generalised ant-repellence. Our results suggest that ant-repellent floral traits may often not be pleiotropic, but instead could have been selected for as a defence against ant thieves in plant species that invest in large volumes of nectar. This conclusion highlights to the importance of research into the cost of nectar production in future studies into ant-flower interactions.

High concentration of nectar quercetin enhances worker resistance to queen's signals in bees.

In honeybee colonies, pheromones produced by the host's queen inhibit worker reproductive potential and queen rearing. Here, we showed that worker bees fed with syrup containing high concentrations of the phenolic quercetin are likely to initiate ovarian development and to build many queen cells in their colony throughout the feeding trial. Workers fed syrup containing high levels of quercetin were aggressive against their queen. Our study suggests that increased phenolic compounds in nectar could enhance worker bee resistance to queen signals in honeybee colonies.