The mechanics of nectar offloading in the bumblebee Bombus terrestris and implications for optimal concentrations during nectar foraging.

Nectar is a common reward provided by plants for pollinators. More concentrated nectar is more rewarding, but also more viscous, and hence more time-consuming to drink. Consequently, theory predicts an optimum concentration for maximizing energy uptake rate, dependent on the mechanics of feeding. For social pollinators such as bumblebees, another important but little-studied aspect of foraging is nectar offloading upon return to the nest. Studying the bumblebee Bombus terrestris, we found that the relationship between viscosity (µ) and volumetric transfer rates (Q) of sucrose solutions differed between drinking and offloading. For drinking, Q ∝ µ-0.180, in good agreement with previous work. Although offloading was quicker than drinking, offloading rate decreased faster with viscosity, with Q ∝ µ-0.502, consistent with constraints imposed by fluid flow through a tube. The difference in mechanics between drinking and offloading nectar leads to a conflict in the optimum concentration for maximizing energy transfer rates. Building a model of foraging energetics, we show that including offloading lowers the maximum rate of energy return to the nest and reduces the concentration which maximizes this rate by around 3%. Using our model, we show that published values of preferred nectar sugar concentrations suggest that bumblebees maximize the overall energy return rather than the instantaneous energy uptake during drinking.This work was supported by a Biotechnology and Biological Sciences Research Council PhD Studentship under grant BB/J014540/1 to J.G.P

Froghoppers jump from smooth plant surfaces by piercing them with sharp spines.

Attachment mechanisms used by climbing animals facilitate their interactions with complex 3D environments and have inspired novel types of synthetic adhesives. Here we investigate one of the most dynamic forms of attachment, used by jumping insects living on plants. Froghopper insects can perform explosive jumps with some of the highest accelerations known among animals. As many plant surfaces are smooth, we studied whether Philaenus spumarius froghoppers are able to take off from such substrates. When attempting to jump from smooth glass, the insects' hind legs slipped, resulting in weak, uncontrolled jumps with a rapid forward spin. By contrast, on smooth ivy leaves and smooth epoxy surfaces, Philaenus froghoppers performed strong jumps without any slipping. We discovered that the insects produced traction during the acceleration phase by piercing these substrates with sharp spines of their tibia and tarsus. High-speed microscopy recordings of hind legs during the acceleration phase of jumps revealed that the spine tips indented and plastically deformed the substrate. On ivy leaves, the spines of jumping froghoppers perforated the cuticle and epidermal cell walls, and wounds could be visualized after the jumps by methylene blue staining and scanning electron microscopy. Improving attachment performance by indenting or piercing plant surfaces with sharp spines may represent a widespread but previously unrecognized strategy utilized by plant-living insects. This attachment mechanism may also provide inspiration for the design of robotic grippers.This study was supported by scholarships from the Gates Cambridge Trust, the Balfour Fund, and the Cambridge Philosophical Society (to H.H.G.), a UK Biotechnology and Biological Research Council PhD Studentship, Grant BB/J014540/1 (to J.G.P.), and UK Biotechnology and Biological Sciences Research Council Grant BB/I008667/1 (to W.F.)

FLORAL SCENT IN A WHOLE-PLANT CONTEXT Floral volatiles controlling ant behaviour

Summary 1. Ants show complex interactions with plants, both facultative and mutualistic, ranging from grazers through seed predators and dispersers to herders of some herbivores and guards against others. But ants are rarely pollinators, and their visits to flowers may be detrimental to plant fitness. 2. Plants therefore have various strategies to control ant distributions, and restrict them to foliage rather than flowers. These 'filters' may involve physical barriers on or around flowers, or 'decoys and bribes' sited on the foliage (usually extrafloral nectaries -EFNs). Alternatively, volatile organic compounds (VOCs) are used as signals to control ant behaviour, attracting ants to leaves and ⁄ or deterring them from functional flowers. Some of the past evidence that flowers repel ants by VOCs has been equivocal and we describe the shortcomings of some experimental approaches, which involve behavioural tests in artificial conditions. 3. We review our previous study of myrmecophytic acacias, which used in situ experiments to show that volatiles derived from pollen can specifically and transiently deter ants during dehiscence, the effects being stronger in ant-guarded species and more effective on resident ants, both in African and Neotropical species. In these plants, repellence involves at least some volatiles that are known components of ant alarm pheromones, but are not repellent to beneficial bee visitors. 4. We also present new evidence of ant repellence by VOCs in temperate flowers, which is usually pollen-based and active on common European ants. We use these data to indicate that across a wide range of plants there is an apparent trade-off in ant-controlling filter strategies between the use of defensive floral volatiles and the alternatives of decoying EFNs or physical barriers

Humans Share More Preferences for Floral Phenotypes With Pollinators Than With Pests.

Studies on the selection of floral traits usually consider pollinators and sometimes herbivores. However, humans also exert selection on floral traits of ornamental plants. We compared the preferences of bumblebees (Bombus terrestris), thrips (Frankliniella occidentalis), and humans for flowers of snapdragon. From a cross of two species, Antirrhinum majus and Antirrhinum linkianum, we selected four Recombinant Inbred Lines (RILs). We characterised scent emission from whole flowers and stamens, pollen content and viability, trichome density, floral shape, size and colour of floral parts. We tested the preferences of bumblebees, thrips, and humans for whole flowers, floral scent bouquets, stamen scent, and individual scent compounds. Humans and bumblebees showed preferences for parental species, whereas thrips preferred RILs. Colour and floral scent, in combination with other floral traits, seem relevant phenotypes for all organisms. Remarkably, visual traits override scent cues for bumblebees, although, scent is an important trait when bumblebees cannot see the flowers, and methyl benzoate was identified as a key attractant for them. The evolutionary trajectory of flowers is the result of multiple floral traits interacting with different organisms with different habits and modes of interaction

How can an understanding of plant-pollinator interactions contribute to global food security?

Pollination of crops by animals is an essential part of global food production, but evidence suggests that wild pollinator populations may be declining while a number of problems are besetting managed honey bee colonies. Animal-pollinated crops grown today, bred in an environment where pollination was less likely to limit fruit set, are often suboptimal in attracting and sustaining their pollinator populations. Research into plant-pollinator interactions is often conducted in a curiosity-driven, ecological framework, but may inform breeding and biotechnological approaches to enhance pollinator attraction and crop yield. In this article we review key topics in current plant-pollinator research that have potential roles in future crop breeding for enhanced global food security

Resolving ant-plant conflicts : mechanisms and functions of floral ant-repellence

Although ants have numerous, often beneficial interactions with plants, as pollinators they are poor. Potential reasons for this include restrictions resulting from their morphology and specific foraging behaviours, and detrimental effects of their surface secretions on pollen. This, coupled with other possible negative effects of ants on floral structures, puts pressure on plants to exclude ants from flowers. One common strategy to achieve this is via behaviour-modifying repellent floral volatiles; however, few studies have identified the volatiles concerned. Here I considered two aspects of this interaction. Firstly, I assessed seven temperate angiosperm species for floral repellence to Formica aquilonia ants using a simple two-way olfactometer. In agreement with previous studies showing that floral ant-repellence is common, significant repellent effects were found in 3/7 species. I also analysed the floral bouquet of Petasites fragrans, a plant previously shown to possess ant-repellent floral volatiles. The most prominent volatile was identified as 4-methoxybenzaldehyde and olfactometer testing of a pure sample of this confirmed it as the likely source of floral repellence in P. fragrans. Although the natural interactions between P. fragrans and ants are unknown, intriguingly 4-methoxybenzaldehyde has been detected from floral volatiles of two further species with frequent ant interactions. A second study compared effects of ants and bees on pollen function to explore the supposed significance of ant-induced reductions in pollen viability. Lily pollen was exposed to either F. aquilonia, Apis mellifera, or Bombus pascuorum, germinated in vitro and assessed for viability. Small, marginally significant reductions in viability were identified for all three insects compared to a control, but with no differences in the reduction between each insect. Although this indicates that the pollen inviability hypothesis for the scarcity of ant pollination may be incorrect, a comparative study with several pollinator and plant species is needed to substantiate this conclusion

Research data supporting “The effect of the 'Bee Gym'(TM) Grooming Device on Varroa destructor Mite Fall from Honey Bee (Apis mellifera) Colonies”

Varroa destructor mite fall over 14 counts from honey bee colonies before (7 counts) and after (7 counts) insertion of a test device (The Bee Gym) or control object. The number of damaged mites is included for the 'counts after'. Data were collected between 30 June and 30 July 2014. The time the drop boards were in place for, for each count, and the time of count are also given.BBSRC [BB/J014540/1], Stuart Roweth (private funder