Large variation among photoreceptors as the basis of visual flexibility in the common backswimmer

The common backswimmer, Notonecta glauca, uses vision by day and night for functions such as underwater prey animal capture and flight in search of new habitats. Although previous studies have identified some of the physiological mechanisms facilitating such flexibility in the animal''s vision, neither the biophysics of Notonecta photoreceptors nor possible cellular adaptations are known. Here, we studied Notonecta photoreceptors using patch-clamp and intracellular recording methods. Photoreceptor size (approximated by capacitance) was positively correlated with absolute sensitivity and acceptance angles. Information rate measurements indicated that large and more sensitive photoreceptors performed better than small ones. Our results suggest that backswimmers are adapted for vision in both dim and well-illuminated environments by having open-rhabdom eyes with large intrinsic variation in absolute sensitivity among photoreceptors, exceeding those found in purely diurnal or nocturnal species. Both electrophysiology and microscopic analysis of retinal structure suggest two retinal subsystems: the largest peripheral photoreceptors provide vision in dim light and the smaller peripheral and central photoreceptors function primarily in sunlight, with light-dependent pigment screening further contributing to adaptation in this system by dynamically recruiting photoreceptors with varying sensitivity into the operational pool.     

Performance of blue- and green-sensitive photoreceptors of the cricket Gryllus bimaculatus

The compound eye of the cricket Gryllus bimaculatus contains a specialized dorsal rim area (DRA) populated by distinct blue-sensitive photoreceptors responsible for perception of polarized light. The rest of the eye is dominated by green-sensitive photoreceptors. Using patch clamp we studied dissociated ommatidia of nocturnal adults and diurnal eight-instar nymphs with the goals (1) of characterizing the biophysical properties of cricket photoreceptors in general and (2) describing the functionally dissimilar blue- and green-sensitive photoreceptors in terms of voltage-gated channel composition and signal coding. Despite different lifestyles, adult and nymph photoreceptors were indistinguishable. No significant circadian changes were observed in K⁺ currents. In contrast, prominent differences were seen between blue- and green-sensitive photoreceptors. The former were characterized by relatively low absolute sensitivity, high input resistance, slow quantum bumps with long latencies, small light-induced and K⁺ currents and low steady-state depolarization. Information rate, a measure of photoreceptor performance calculated from voltage responses to bandwidth-limited white noise-modulated light contrast, was 87 ± 8 bits s^?1 in green-sensitive photoreceptors vs. 59 ± 14 bits s^?1 in blue-sensitive photoreceptors, implying a limited role of DRA in the perception of visual contrasts. In addition, evidence of electrical coupling between photoreceptors is presented.     

Pollen diets and niche overlap of honey bees and native bees in protected areas

The decline of both managed and wild bee populations has been extensively reported for over a decade now, with growing concerns amongst the scientific community. Also, evidence is growing that both managed and feral honey bees may exacerbate threats to wild bees. In Australia, there are over 1600 native bee species and introduced European honey bees (Apis mellifera) have established throughout most landscapes. There is a major gap in knowledge of the interactions between honey bees and native bees in Australian landscapes, especially floral resource use.Here we report on the pollen diets of wild bees in protected areas of coastal heathland, an ecosystem characterised by mass flowering in late winter and spring. We sampled bees within three sites and DNA metabarcoding was used to compare the pollen diets of honey bees and native bees. We recorded 2, 772 bees in total, with 13 genera and 18 described species identified. Apis mellifera was the most common species across all locations, accounting for 42% of all bees collected. Native bee genera included eusocial Tetragonula (stingless bees) (37%), and semi-social Exoneura and Braunsapis (19.8% combined). Metabarcoding data revealed both Tetragonula and honey bees have wide foraging patterns, and the bipartite network overall was highly generalised (H₂’ = 0.24). Individual honey bees carried pollen of 7–29 plant species, and significantly more species than all other bees. We found niche overlap in the diets of honey bees and native bees generally (0.42), and strongest overlap with stingless bees (0.70) and species of Braunsapis (0.62). A surprising finding was that many species carried pollen from Restionaceae and Cyperaceae, families generally considered to be predominantly wind-pollinated in Australia. Our study showed introduced honey bee use of resources overlaps with that of native bees in protected heathlands, but there are clear differences in their diet preferences.     

Differential sensitivity of honey bees and bumble bees to a dietary insecticide (imidacloprid)

Currently, there is concern about declining bee populations and the sustainability of pollination services. One potential threat to bees is the unintended impact of systemic insecticides, which are ingested by bees in the nectar and pollen from flowers of treated crops. To establish whether imidacloprid, a systemic neonicotinoid and insect neurotoxin, harms individual bees when ingested at environmentally realistic levels, we exposed adult worker bumble bees, Bombus terrestris L. (Hymenoptera: Apidae), and honey bees, Apis mellifera L. (Hymenoptera: Apidae), to dietary imidacloprid in feeder syrup at dosages between 0.08 and 125 μg l^?1. Honey bees showed no response to dietary imidacloprid on any variable that we measured (feeding, locomotion and longevity). In contrast, bumble bees progressively developed over time a dose-dependent reduction in feeding rate with declines of 10–30% in the environmentally relevant range of up to 10 μg l^?1, but neither their locomotory activity nor longevity varied with diet. To explain their differential sensitivity, we speculate that honey bees are better pre-adapted than bumble bees to feed on nectars containing synthetic alkaloids, such as imidacloprid, by virtue of their ancestral adaptation to tropical nectars in which natural alkaloids are prevalent. We emphasise that our study does not suggest that honey bee colonies are invulnerable to dietary imidacloprid under field conditions, but our findings do raise new concern about the impact of agricultural neonicotinoids on wild bumble bee populations.     

Acetylcholinesterase in Apis mellifera head during post-embryonic development. Existence of a glycoinositol-anchored membrane form at eary pupal stages

• 1.1. Properties of acetylcholinesterase (AChE, EC 3.1.1.7) from Apis mellifera head were studied during pupal development and at the adult stage.
• 2.2. During post-embryonic development, tissue and specific activities were closely related and increased to reach a maximum value at emergence and at last pupal stage, respectively.
• 3.3. In adults, AChE activity was weaker in foragers than in emerging bees.
• 4.4. The membrane form occurred in adult bees as well as in pupae whereas the soluble enzyme only appeared from Pd pupal stage.
• 5.5. The proportion of soluble and membrane forms fluctuated during late development but, in all cases, the percentage of the soluble form remained less than 10% of total AChE activity.
• 6.6. At all post-embryonic stages, the membrane form was sensitive to the action of phosphatidylinositol-specific phospholipase C (PI-PLC) and was converted into a hydrophilic enzyme.
• 7.7. In adult bees, the sensitivity to PI-PLC depended on the season. In summer, about 60% of the membrane activity could be solubilized by PI-PLC vs only 5% in winter.
• 8.8. The sensitivity of AChE to pirimicarb varied with the developmental stage.
• 9.9. In foraging bees, AChE was more susceptible to pirimicarb than in emerging bees. This difference of sensitivity to carbamate was abolished after removal of the membrane anchor either by mild trypsin digestion of PI-PLC treatment.

     

A Light-Oxygen-Voltage Receptor Integrates Light and Temperature

Sensory photoreceptors enable organisms to adjust their physiology, behavior, and development in response to light, generally with spatiotemporal acuity and reversibility. These traits underlie the use of photoreceptors as genetically encoded actuators to alter by light the state and properties of heterologous organisms. Subsumed as optogenetics, pertinent approaches enable regulating diverse cellular processes, not least gene expression. Here, we controlled the widely used Tet repressor by coupling to light-oxygen-voltage (LOV) modules that either homodimerize or dissociate under blue light. Repression could thus be elevated or relieved, and consequently protein expression was modulated by light. Strikingly, the homodimeric RsLOV module from Rhodobacter sphaeroides not only dissociated under light but intrinsically reacted to temperature. The limited light responses of wild-type RsLOV at 37 °C were enhanced in two variants that exhibited closely similar photochemistry and structure. One variant improved the weak homodimerization affinity of 40 µM by two-fold and thus also bestowed light sensitivity on a receptor tyrosine kinase. Certain photoreceptors, exemplified by RsLOV, can evidently moonlight as temperature sensors which immediately bears on their application in optogenetics and biotechnology. Properly accounted for, the temperature sensitivity can be leveraged for the construction of signal-responsive cellular circuits.     

Adaptation in Skate Photoreceptors

Receptor potentials were recorded extracellularly from the all-rod retina of the skate after the application of sodium aspartate. This agent suppresses the responses of proximal elements, but leaves relatively unaffected the electrical activity of the photoreceptors (a-wave) and pigment epithelium (c-wave). Since the latter develops too slowly to interfere with the receptor response, it was possible to isolate receptor potentials and to compare their behavior in light and dark adaptation with earlier observations on the S-potential, b-wave, and ganglion cell discharge. The results show that the photoreceptors display the full complement of adaptational changes exhibited by cells proximal to the receptors. Thus, it appears that visual adaptation in the skate is governed primarily by the photoreceptors themselves. Of particular interest was the recovery of sensitivity in the presence of background fields that initially saturate the receptor potential. Analysis of this recovery phase indicates that a gain-control mechanism operates within the receptors, at a distal stage of the visual process.     

Monitoring bee populations: are eusocial bees attracted to different colours of pan trap than other bees?

Declines in pollinator populations have made monitoring pollinators, in particular bees, increasingly important. There is general agreement among practitioners that using a mix of trap colours is important, but the empirical evidence to support this is scattered. During studies of bees in forestry cutovers, large differences were noted in capture rate among white, blue, and yellow pan traps. Pooled data from collections in cutovers and commercial cranberry fields demonstrated significant differences in the effect of trap colour, with the largest numbers captured in white traps, and the fewest in yellow, but only for the genus Bombus Latreille (Hymenoptera: Apidae). The colour preference was consistent with the spectral sensitivity of Bombus, and the visible reflectance spectra of the traps. A literature review suggested that among eusocial bees, Apis Linnaeus (Hymenoptera: Apidae) are more attracted to white traps and Bombus are more attracted to blue traps, while non-eusocial bees with a variety of social structures are more attracted to yellow. Among the non-eusocial bees, Halictidae were somewhat attracted to blue, while Andrenidae were not. This supports the common practice of using white, blue, and yellow traps when surveying bees to ensure adequate taxonomic representation.     

Larger bees facilitate the deposition of oilseed rape pollen (Brassica napus L.)

Oilseed rape is the third-largest source of vegetable oil and the second-largest source of protein meal in the world. Pollinators are vital in the production of oilseed rape. However, pollination efficiency could be influenced by the morphology and foraging behaviors of pollinators. To evaluate the effect of pollinator size and foraging behavior on pollination efficiency, the intertegular distances (ITDs) of five bumble bees (Bombus pyrosoma, B. lantschouensis, B. melanurus, B. sichelii and B. sibiricus) and two honey bees (Apis mellifera and A. cerana) were evaluated. Their foraging activities and single visit depositions (SVDs) on oilseed rape were observed and counted. The ITDs of bumble bees were significantly larger than honey bees (P < 0.05). The single-visit duration of A. mellifera (2.43 ± 0.06 s) was significantly longer than other bees (P < 0.05). The interval time of the A. cerana was longer than other bees (P < 0.05). Larger bees tended to deposit more pollen on stigmas at each visit than smaller bees. The interspecific ITD of bees had a positive effect on SVD (P < 0.001). There was no correlation between ITD and SVD among individuals of the same species. In conclusion, the size of bees had a positive impact on pollination efficiency. Bees with a greater ITD deposited substantially more pollen and had a significantly shorter interval between flowers. Understanding the foraging behavior and pollination efficiency of these bee species and developing habitats to support them should enable growers to achieve resilient production.     

A presumed case of functional convergence between the flowers of Schizolobium parahyba (Fabaceae) and species of Malpighiaceae

Flowers of Malpighiaceae have a flag petal with a sturdy base that Centridini bees clasp with their mandibles to free their legs and thus be able to harvest oil. We found that the yellow, nectariferous flowers of Schizolobium parahyba (Fabaceae) have a forward-flexed upper petal with a sturdy claw and an adnate filament. Two Centris species were among the most frequent bee visitors to S. parahyba flowers. These bees clasped the adnate filament and the claw of the upper petal with their mandibles and extended their mouthparts into the corolla to take nectar. During the visit they leaned on, or loosely grabbed, the stamens. Blooming in the same area and period were two yellow-flowered Stigmaphyllon species (Malpighiaceae) whose pollen was also found on loads carried by the Centris bees. The flexion and the sturdiness of the upper petal claw of Schizolobium parahyba flowers may be viewed as a trait that suits the mandible clasp of Centris bees. Although this clasp is not needed when the bees visit S. parahyba flowers, it is vital when the bees exploit flowers of the Malpighiaceae. We suggest that the sturdy claw and the adnate filament of S. parahyba may be viewed as an instance of presumed functional convergence with the upper petal of Malpighiaceae.     

Coexpression of three middle wavelength-absorbing visual pigments in sexually dimorphic photoreceptors of the butterfly Colias erate

The tiered ommatidia of the Eastern Pale Clouded yellow butterfly, Colias erate, contain nine photoreceptor cells, four of which contribute their rhabdomeral microvilli to the distal tier of the rhabdom. We analyzed the visual pigments and spectral sensitivities of these distal photoreceptors in both sexes of Colias erate. A subset of photoreceptor cells expresses a newly discovered middle wavelength-absorbing opsin, C olias e rate Blue (CeB), in addition to two previously described middle wavelength-absorbing opsins, CeV1 and CeV2. The other photoreceptors either coexpress CeV1 and CeV2, or exclusively express a short wavelength-absorbing opsin, CeUV, or a long wavelength-absorbing opsin, CeL. Males and females have the same visual pigment expression patterns, but the photoreceptor spectral sensitivities are sexually dimorphic. The photoreceptors coexpressing three middle wavelength-absorbing opsins are broad-blue receptors in males, but in females they are narrow-blue receptors. Those with CeV1 and CeV2 are violet receptors in females, while they are shouldered-blue receptors in males. The sexual dimorphism in spectral sensitivity is caused by a sex-specific distribution of fluorescent pigment that functions as a spectral filter.     

Opsin expression patterns coincide with photoreceptor development during pupal development in the honey bee,Apis mellifera

The compound eyes of insects allow them to catch photons and convert the energy into electric signals. All compound eyes consist of numerous ommatidia, each comprising a fixed number of photoreceptors. Different ommatidial types are characterized by a specific set of photoreceptors differing in spectral sensitivity. In honey bees, males and females possess different ommatidial types forming distinct retinal mosaics. However, data are lacking on retinal ontogeny and the mechanisms by which the eyes are patterned. In this study, we investigated the intrinsic temporal and circadian expression patterns of the opsins that give rise to the ultraviolet, blue and green sensitive photoreceptors, as well as the morphological maturation of the retina during pupal development of honey bees. qPCR and histological labeling revealed that temporal opsin mRNA expression differs between sexes and correlates with rhabdom elongation during photoreceptor development. In the first half of the pupal stage, when the rhabdoms of the photoreceptors are still short, worker and (dorsal) drone retinae exhibit similar expression patterns with relatively high levels of UV (UVop) and only marginal levels of blue (BLop) and green (Lop1) opsin mRNA. In the second half of pupation, when photoreceptors and rhabdoms elongate, opsin expression in workers becomes dominated by Lop1 mRNA. In contrast, the dorsal drone eye shows high expression levels of UVop and BLop mRNA, whereas Lop1 mRNA level decreases. Interestingly, opsin expression levels increase up to 22-fold during early adult life. We also found evidence that opsin expression in adult bees is under the control of the endogenous clock. Our data indicate that the formation of the sex-specific retinal composition of photoreceptors takes place during the second half of the pupal development, and that opsin mRNA expression levels continue to increase in young bees, which stands in contrast to Drosophila, where the highest expression levels are found during the late pupal stage and remain constant in adults. From an evolutionary perspective, we hypothesize that the delayed retinal maturation during the early adult phase is linked to the delayed transition from indoor to outdoor activities in bees, when vision becomes important.     

Retinal degeneration-3 protein attenuates photoreceptor degeneration in transgenic mice expressing dominant mutation of human retinal guanylyl cyclase

Different forms of photoreceptor degeneration cause blindness. Retinal degeneration-3 protein (RD3) deficiency in photoreceptors leads to recessive congenital blindness. We proposed that aberrant activation of the retinal membrane guanylyl cyclase (RetGC) by its calcium-sensor proteins (guanylyl cyclase–activating protein [GCAP]) causes this retinal degeneration and that RD3 protects photoreceptors by preventing such activation. We here present in vivo evidence that RD3 protects photoreceptors by suppressing activation of both RetGC1 and RetGC2 isozymes. We further suggested that insufficient inhibition of RetGC by RD3 could contribute to some dominant forms of retinal degeneration. The R838S substitution in RetGC1 that causes autosomal-dominant cone–rod dystrophy 6, not only impedes deceleration of RetGC1 activity by Ca²⁺GCAPs but also elevates this isozyme''s resistance to inhibition by RD3. We found that RD3 prolongs the survival of photoreceptors in transgenic mice harboring human R838S RetGC1 (R838S⁺). Overexpression of GFP-tagged human RD3 did not improve the calcium sensitivity of cGMP production in R838S⁺ retinas but slowed the progression of retinal blindness and photoreceptor degeneration. Fluorescence of the GFP-tagged RD3 in the retina only partially overlapped with immunofluorescence of RetGC1 or GCAP1, indicating that RD3 separates from the enzyme before the RetGC1:GCAP1 complex is formed in the photoreceptor outer segment. Most importantly, our in vivo results indicate that, in addition to the abnormal Ca²⁺ sensitivity of R838S RetGC1 in the outer segment, the mutated RetGC1 becomes resistant to inhibition by RD3 in a different cellular compartment(s) and suggest that RD3 overexpression could be utilized to reduce the severity of cone–rod dystrophy 6 pathology.     

Effect of royal jelly on longevity and memory-related traits of Apis mellifera workers

Royal jelly (RJ) is a key factor for honey bee caste determination. The queen bee is fed with RJ by worker bees throughout her life, while the worker bees eat bee bread themselves. This study was designed to explore the effect of nutrient-rich RJ on longevity and learning and memory abilities of workers of the western honey bee Apis mellifera. The newly emerged worker bees were randomly divided into three groups and were fed 50% sucrose solution containing 0%, 10%, and 20% RJ. We found that worker bees fed with 10% and 20% RJ showed significantly improved longevity and higher proboscis extension response success rate compared to bees fed with 50% sucrose containing 0% RJ. Additionally, bees fed with 20% RJ showed significantly higher level of expression of memory related genes (GluRA and Nmdar1) compared to the control group. Furthermore, expression of the Nmdar1 gene of worker bees fed with 10% RJ was also significantly higher than in the control group. These results indicate that RJ has potential effects on the longevity and learning and memory abilities of A. mellifera.     

Multi-Drug Resistance Transporters and a Mechanism-Based Strategy for Assessing Risks of Pesticide Combinations to Honey Bees

Annual losses of honey bee colonies remain high and pesticide exposure is one possible cause. Dangerous combinations of pesticides, plant-produced compounds and antibiotics added to hives may cause or contribute to losses, but it is very difficult to test the many combinations of those compounds that bees encounter. We propose a mechanism-based strategy for simplifying the assessment of combinations of compounds, focusing here on compounds that interact with xenobiotic handling ABC transporters. We evaluate the use of ivermectin as a model substrate for these transporters. Compounds that increase sensitivity of bees to ivermectin may be inhibiting key transporters. We show that several compounds commonly encountered by honey bees (fumagillin, Pristine, quercetin) significantly increased honey bee mortality due to ivermectin and significantly reduced the LC₅₀ of ivermectin suggesting that they may interfere with transporter function. These inhibitors also significantly increased honey bees sensitivity to the neonicotinoid insecticide acetamiprid. This mechanism-based strategy may dramatically reduce the number of tests needed to assess the possibility of adverse combinations among pesticides. We also demonstrate an in vivo transporter assay that provides physical evidence of transporter inhibition by tracking the dynamics of a fluorescent substrate of these transporters (Rhodamine B) in bee tissues. Significantly more Rhodamine B remains in the head and hemolymph of bees pretreated with higher concentrations of the transporter inhibitor verapamil. Mechanism-based strategies for simplifying the assessment of adverse chemical interactions such as described here could improve our ability to identify those combinations that pose significantly greater risk to bees and perhaps improve the risk assessment protocols for honey bees and similar sensitive species.     

Perception of floral volatiles involved in host-plant finding behaviour: comparison of a bee specialist and generalist

Specialist and generalist bees use olfactory and visual cues to find and recognise flowering plants. Specialised (oligolectic) bees rely on few host plants for pollen collection. These bee species are suggested to use specific volatiles, but it is unknown whether they have dedicated adaptations for these particular compounds compared to bees not specialised on the same plants. In the present study, we investigated the perception of host odorants and its neuronal substrate with regard to host-plant finding behaviour in oligolectic bees. We reconstructed the antennal lobes (AL) in the Salix specialist, Andrena vaga, and counted about 135 glomeruli and thereby less than the approximately 160 in honeybees. Using calcium imaging experiments to measure neural activity in the bee brain, we recorded odorant-evoked activity patterns in the AL of A. vaga and, for comparison, in the generalist honeybee, Apis mellifera. Our physiological experiments demonstrated that A. vaga bees were particularly sensitive to 1,4-dimethoxybenzene, a behaviour-mediating odorant of Salix host flowers. We found more sensitive glomeruli in the specialised bees as compared to generalist honeybees. This neural adaptation might allow oligolectic A. vaga bees to effectively locate host plants from distances.     

Visual reliability and information rate in the retina of a nocturnal bee

Nocturnal animals relying on vision typically have eyes that are optically and morphologically adapted for both increased sensitivity and greater information capacity in dim light. Here, we investigate whether adaptations for increased sensitivity also are found in their photoreceptors by using closely related and fast-flying nocturnal and diurnal bees as model animals. The nocturnal bee Megalopta genalis is capable of foraging and homing by using visually discriminated landmarks at starlight intensities. Megalopta's near relative, Lasioglossum leucozonium, performs these tasks only in bright sunshine. By recording intracellular responses to Gaussian white-noise stimuli, we show that photoreceptors in Megalopta actually code less information at most light levels than those in Lasioglossum. However, as in several other nocturnal arthropods, Megalopta's photoreceptors possess a much greater gain of transduction, indicating that nocturnal photoreceptors trade information capacity for sensitivity. By sacrificing photoreceptor signal-to-noise ratio and information capacity in dim light for an increased gain and, thus, an increased sensitivity, this strategy can benefit nocturnal insects that use neural summation to improve visual reliability at night.     

The Honey Bee Parasite Nosema ceranae: Transmissible via Food Exchange?

Nosema ceranae, a newly introduced parasite of the honey bee, Apis mellifera, is contributing to worldwide colony losses. Other Nosema species, such as N. apis, tend to be associated with increased defecation and spread via a fecal-oral pathway, but because N. ceranae does not induce defecation, it may instead be spread via an oral-oral pathway. Cages that separated older infected bees from young uninfected bees were used to test whether N. ceranae can be spread during food exchange. When cages were separated by one screen, food could be passed between the older bees and the young bees, but when separated by two screens, food could not be passed between the two cages. Young uninfected bees were also kept isolated in cages, as a solitary control. After 4 days of exposure to the older bees, and 10 days to incubate infections, young bees were more likely to be infected in the 1-Screen Test treatment vs. the 2-Screen Test treatment (P = 0.0097). Young bees fed by older bees showed a 13-fold increase in mean infection level relative to young bees not fed by older bees (1-Screen Test 40.8%; 2-Screen Test 3.4%; Solo Control 2.8%). Although fecal-oral transmission is still possible in this experimental design, oral-oral infectivity could help explain the rapid spread of N. ceranae worldwide.     

The pollination efficiency of a pollinator depends on its foraging strategy,flowering phenology,and the flower characteristics of a plant species

Honey bees and stingless bees are generalist visitors of several wild and cultivated plants. They forage with a high degree of floral fidelity and thereby help in the pollination services of those plants. We hypothesized that pollination efficiency might be influenced by flowering phenology, floral characteristics, and resource collection modes of the worker bees. In this paper, we surveyed the foraging strategies of honey bees (Apis cerana, Apis dorsata, and Apis florea) and stingless bees (Tetragonula iridipennis) concerning their pollination efficiencies. Bees showed different resource gathering strategies, including legitimate (helping in pollination as mixed foragers and specialized foragers) and illegitimate (serving as nectar robbers and pollen thieves) types of flower visitation patterns. Foraging strategies are influenced by the shape of flowers, the timing of the visitation, floral richness, and bee species. Honey bees and stingless bees mainly acted as legitimate visitors in most plants studied. Sometimes honey bees served as nectar robbers in tubular flowers and stingless bees as pollen thieves in large-sized flowers. Among the legitimate categories, mixed foragers have a comparatively lower flower visitation rate than the specialized nectar and pollen foragers. However, mixed foragers have greater abundance and higher values of the single-visit pollination efficiency index (PEi) than nectar and pollen foragers. The value of the combined parameter ‘importance in pollination (PI)’ was thus higher in mixed foragers than in nectar and pollen foragers.