Recent reports of global declines in pollinator species imply an urgent need to assess the abundance of native pollinators and density-dependent benefits for linked plants. In this study, we ...investigated (1) pollinator nest distributions and estimated colony abundances, (2) the relationship between abundances of foraging workers and the number of nests they represent, (3) pollinator foraging ranges, and (4) the relationship between pollinator abundance and plant reproduction. We examined these questions in an alpine ecosystem in the Colorado Rocky Mountains, focusing on four alpine bumble bee species (
Bombus balteatus
,
B. flavifrons
,
B. bifarius
, and
B. sylvicola
), and two host plants that differ in their degrees of pollinator specialization (
Trifolium dasyphyllum
and
T. parryi
).
Using microsatellites, we found that estimated colony abundances among
Bombus
species ranged from ~18 to 78 colonies/0.01 km
2
. The long-tongued species
B. balteatus
was most common, especially high above treeline, but the subalpine species
B. bifarius
was unexpectedly abundant for this elevation range. Nests detected among sampled foragers of each species were correlated with the number of foragers caught. Foraging ranges were smaller than expected for all
Bombus
species, ranging from 25 to 110 m. Fruit set for the specialized plant,
Trifolium parryi
, was positively related to the abundance of its
Bombus
pollinator. In contrast, fruit set for the generalized plant,
T. dasyphyllum
, was related to abundance of all
Bombus
species. Because forager abundance was related to nest abundance of each
Bombus
species and was an equally effective predictor of plant fecundity, forager inventories are probably suitable for assessing the health of outcrossing plant populations. However, nest abundance, rather than forager abundance, better reflects demographic and genetic health in populations of eusocial pollinators such as bumble bees. Development of models incorporating the parameters we have measured here (nest abundance, forager abundance, and foraging distance) could increase the usefulness of foraging worker inventories in monitoring, managing, and conserving pollinator populations.
There is considerable and ongoing debate as to the harm inflicted on bees by exposure to agricultural pesticides. In part, the lack of consensus reflects a shortage of information on field-realistic ...levels of exposure. Here, we quantify concentrations of neonicotinoid insecticides and fungicides in the pollen of oilseed rape, and in pollen of wildflowers growing near arable fields. We then compare this to concentrations of these pesticides found in pollen collected by honey bees and in pollen and adult bees sampled from bumble bee colonies placed on arable farms. We also compared this with levels found in bumble bee colonies placed in urban areas. Pollen of oilseed rape was heavily contaminated with a broad range of pesticides, as was the pollen of wildflowers growing nearby. Consequently, pollen collected by both bee species also contained a wide range of pesticides, notably including the fungicides carbendazim, boscalid, flusilazole, metconazole, tebuconazole and trifloxystrobin and the neonicotinoids thiamethoxam, thiacloprid and imidacloprid. In bumble bees, the fungicides carbendazim, boscalid, tebuconazole, flusilazole and metconazole were present at concentrations up to 73nanogram/gram (ng/g). It is notable that pollen collected by bumble bees in rural areas contained high levels of the neonicotinoids thiamethoxam (mean 18ng/g) and thiacloprid (mean 2.9ng/g), along with a range of fungicides, some of which are known to act synergistically with neonicotinoids. Pesticide exposure of bumble bee colonies in urban areas was much lower than in rural areas. Understanding the effects of simultaneous exposure of bees to complex mixtures of pesticides remains a major challenge.
•Pollen of oilseed rape and wildflowers growing nearby contained a wide range of pesticides.•Pollen collected by honeybees and bumblebees also contained a broad range of pesticides.•Pesticide exposure of bumblebee colonies in urban areas was lower than in rural areas.
•Structural complexity enhancement promoted bees in coniferous forest.•Aboveground, solitary and cuckoo bees reacted positively to creation of deadwood.•Bilberry cover on plot scale and meadows on ...landscape scale support bees in forests.•Creation of deadwood is a viable conservation measure for some wild bees in forests.
Structural complexity enhancement (SCE) is a forest restoration approach aiming to maintain or increase biodiversity in managed, secondary forests. Whether the diversity of wild bees also benefits from such restoration measures in temperate forests is not well studied. We conducted a restoration experiment in secondary spruce forests on twelve 50 × 50 m plots in the Black Forest National Park in Baden-Württemberg, Germany. SCE was carried out on half of the study plots (six) in 2016 comprised create deadwood through girdling and uprooting of 20 spruce trees per plot and thus initiating small gaps. The other six plots were used as control plots with no SCE. Wild bees were sampled in June 2018 and 2019 using coloured pan traps. We hypothesized that creation of deadwood influences bee abundance and richness, especially of aboveground-nesting bees, and thus would also change bee community composition at the plot scale. Furthermore, we assessed the influence of bilberry (Vaccinium myrtillus L.) cover in the plots and areas of meadows and roads of the intermediate surrounding on wild bees.
Estimated species richness was higher on restored plots than on control plots. Deadwood originating from restoration increased the number of aboveground-nesting, solitary and cuckoo bee individuals. In particular standing deadwood had a positive impact on bee individuals. Increased bilberry cover and nearby meadow areas increased abundance and richness of the bee community.
We conclude that creation of deadwood in coniferous forest is a promising restoration measure to promote solitary, aboveground-nesting bees. Increased light availability through restoration, which promotes bilberry flowering, is also beneficial for bees.
Bumble bees are globally important pollinators, especially in temperate regions, and evidence suggests that many species are declining. One recent high profile study by Soroye et al. (2020) applied ...occupancy models to dated historical collection data to quantify declines across North America and Europe. The authors modelled 66 species across a set of sites spanning both North America and Europe, rather than confining species to sites where they might be expected to occur. In addition, they inferred non-detections for time intervals where there is no evidence that the site was visited (by forcing every site to have exactly 3 visits in each era). We use simulated data to (i) investigate the validity of methods used in that study and (ii) test whether a multi-species framework that incorporates species' ranges and site visitation histories produces better estimates. We show that the method used by Soroye et al. (2020) yields biased estimates of declines, whereas our framework does not. We use such a model to provide revised and appreciably lower estimates for bumble bee community declines, with species-specific trends more closely matching classifications from IUCN. The species level trends we provide can help inform future species-at-risk assessments. Well-parameterized occupancy models may be a powerful tool for assessing species-wide trends using curated historical collection data.
The acute decline in global biodiversity includes not only the loss of rare species, but also the rapid collapse of common species across many different taxa. The loss of pollinating insects is of ...particular concern because of the ecological and economic values these species provide. The western bumble bee (
) was once common in western North America, but this species has become increasingly rare through much of its range. To understand potential mechanisms driving these declines, we used Bayesian occupancy models to investigate the effects of climate and land cover from 1998 to 2020, pesticide use from 2008 to 2014, and projected expected occupancy under three future scenarios. Using 14,457 surveys across 2.8 million km
in the western United States, we found strong negative relationships between increasing temperature and drought on occupancy and identified neonicotinoids as the pesticides of greatest negative influence across our study region. The mean predicted occupancy declined by 57% from 1998 to 2020, ranging from 15 to 83% declines across 16 ecoregions. Even under the most optimistic scenario, we found continued declines in nearly half of the ecoregions by the 2050s and mean declines of 93% under the most severe scenario across all ecoregions. This assessment underscores the tenuous future of
and demonstrates the scale of stressors likely contributing to rapid loss of related pollinator species throughout the globe. Scaled-up, international species-monitoring schemes and improved integration of data from formal surveys and community science will substantively improve the understanding of stressors and bumble bee population trends.
Display omitted
•Gonadotropic effect of JH varies between species, caste and queen hibernation status.•JH application stimulates ovary development of non-hibernated queens.•A higher JH dose is needed ...to elicit a gonadotropic effect in B. impatiens than in B. terrestris.•No gonadotropic effect of JH found in newly hatched workers.•JH alone does not affect queen egg laying; additional stimuli required for colony initiation.
Juvenile hormone (JH) regulates developmental and physiological processes in insects. In bumble bees, the hormone acts as a gonadotropin that mediates ovary development, but the exact physiological pathways involved in ovary activation and subsequent egg laying are poorly understood. In this study, we examine how queen hibernation state, caste, and species impact the gonadotropic effect of JH in bumble bee queens through methoprene (JH analogue) application. We extend previous research by assessing queen egg laying and colony initiation, alongside ovary development. Furthermore, we compared sensitivity of workers of both species to the juvenile hormone's gonadotropic effect. In both bumble bee species, the ovaries of hibernated queens were developed five to six days after breaking diapause, regardless of methoprene treatment. By contrast, methoprene did have a stimulatory effect on ovary development in non-hibernated queens. The dose needed to obtain this effect was higher in B. impatiens. Methoprene did not have gonadotropic effects in callow workers of both species. These results indicate that the physiological effect of exogenous methoprene application varies according to species, caste and hibernation status. Interestingly, despite gonadotropic effects in non-hibernated queens, oviposition was not accelerated by JH. This suggests that JH alone is insufficient to induce egg laying and that an additional stimulus, which is naturally present in hibernated queens, is required. Consequently, our findings indicate that other physiological processes, beyond a rise in JH alone, are required for oviposition and colony initiation.
Caffeine is a widely occurring plant defense chemical1,2 that occurs in the nectar of some plants, e.g., Coffea or Citrus spp., where it may influence pollinator behavior to enhance pollination.3,4 ...Honey bees fed caffeine form longer lasting olfactory memory associations,5 which could give plants with caffeinated nectar an adaptive advantage by inducing more visits to flowers. Caffeinated free-flying bees show enhanced learning performance6 and are more likely to revisit a caffeinated target feeder or artificial flower,7–9 although it is not clear whether improved memory of the target cues or the perception of caffeine as a reward is the cause. Here, we show that inexperienced bumble bees (Bombus terrestris) locate new food sources emitting a learned floral odor more consistently if they have been fed caffeine. In laboratory arena tests, we fed bees a caffeinated food alongside a floral odor blend (priming) and then used robotic experimental flowers10 to disentangle the effects of caffeine improving memory for learned food-associated cues versus caffeine as a reward. Inexperienced bees primed with caffeine made more initial visits to target robotic flowers emitting the target odor compared to control bees or those primed with odor alone. Caffeine-primed bees tended to improve their floral handling time faster. Although the effects of caffeine were short lived, we show that food-locating behaviors in free-flying bumble bees can be enhanced by caffeine provided in the nest. Consequently, there is potential to redesign commercial colonies to enhance bees’ forage focus or even bias bees to forage on a specific crop.
Display omitted
•We primed bumble bees with caffeine, sucrose solution, and a floral odor•Caffeine-treated bees made more initial visits to odor-associated target flowers•Our data inform the development of precision pollination technology
Arnold et al. demonstrate that bumble bees provided with caffeinated food in the nest alongside a floral odor blend preferentially seek out targets of matching odor outside the nest more often than will bees that have not been exposed to caffeine. This allows bees to be primed to target specific odors.
Exposure effects of Beauveria bassiana strain Bb-1 (Nostalgist), Isaria fumosorosea (= Paecilomyces fumosoroseus) strain PFs-1 (Priority), Lecanicillium lecanii strain V1-1 (Nibortem), azadirachtin ...(Nimbecidine) and Bacillus thuringiensis var. kurstaki (Rebound) on Bombus terrestris workers were investigated under laboratory conditions. Bombus terrestris workers were exposed to the recommended doses of biopesticides orally via feeding treated sugar syrup and treated pollen, a total of 600 individuals were used during the study. The experiments were carried out between September and November 2019 in the Research and Application laboratory of apiculture in the Department of Animal Science in Isparta University of Applied Sciences, Turkey. It was found that observed side effects differ in terms of the application methods of the biopesticides. Although worker mortalities ranged between 6 and 16% (non-toxic) in treated pollen, mortality rates 100% (highly toxic) for B.t. var. kurstaki and azadirachtin, 44% (weakly toxic) for I. f. strain PFs-1 and 8-14% (non-toxic) for other biopesticides in treated sugar syrup. The results showed that the biopesticides other than Rebound and Nimbecidine were not toxic on workers of B. terrestris in laboratory conditions.
Display omitted
•Pollen contains a mixture of fatty acids (FA) with different saturation.•Bumble bees poorly absorbed palmitate, common FA in pollen of many plants.•Unsaturated oleic and linoleic ...acids are better absorbed and oxidized by Bumble bees.•The pollen consumption rate did not vary among the three pollen-enriched FAs diets.•Pollen is unlikely to have been nutritionally optimized for Bumble bees.
Pollen serves as a crucial source of protein and lipids for numerous insects. Despite the importance of pollen lipids for nutrient regulation in bees, the digestibility and absorption of different fatty acids (FAs) by bees remain poorly understood. We used 13C labeled fatty acids (FAs) to investigate the absorption and allocation of three common dietary FAs in pollen by bumble bees. Palmitic acid, the most common saturated FA in pollen, was poorly absorbed, even when supplied as tripalmitate, emulsified, or mixed in vegetable oil. In contrast, the essential linoleic acid was absorbed and allocated at the highest rate among the three FAs tested. Oleic acid, a non-essential monounsaturated FA, was absorbed and oxidized at lower rates than linoleic acid. Notably, a feeding rate experiment revealed that different fatty acids did not affect the consumption rate of pollen. This results suggests that the specific FA's absorption efficiency and allocation differ in bumble bees, impacting their utilization. These findings demonstrate the importance of considering the digestibility and absorption of different FAs. Furthermore, the study highlights the influence of pollen lipid composition on the nutritional content for pollinators and raises questions about the utilization of polyunsaturated FAs in insect metabolism.
PDF
