Honey bees and wild pollinators differ in their preference for and use of introduced floral resources

Introduced plants may be important foraging resources for honey bees and wild pollinators, but how often and why pollinators visit introduced plants across an entire plant community is not well understood. Understanding the importance of introduced plants for pollinators could help guide management of these plants and conservation of pollinator habitat. We assessed how floral abundance and pollinator preference influence pollinator visitation rate and diversity on 30 introduced versus 24 native plants in central New York. Honey bees visited introduced and native plants at similar rates regardless of floral abundance. In contrast, as floral abundance increased, wild pollinator visitation rate decreased more strongly for introduced plants than native plants. Introduced plants as a group and native plants as a group did not differ in bee diversity or preference, but honey bees and wild pollinators preferred different plant species. As a case study, we then focused on knapweed (Centaurea spp.), an introduced plant that was the most preferred plant by honey bees, and that beekeepers value as a late‐summer foraging resource. We compared the extent to which honey bees versus wild pollinators visited knapweed relative to coflowering plants, and we quantified knapweed pollen and nectar collection by honey bees across 22 New York apiaries. Honey bees visited knapweed more frequently than coflowering plants and at a similar rate as all wild pollinators combined. All apiaries contained knapweed pollen in nectar, 86% of apiaries contained knapweed pollen in bee bread, and knapweed was sometimes a main pollen or nectar source for honey bees in late summer. Our results suggest that because of diverging responses to floral abundance and preferences for different plants, honey bees and wild pollinators differ in their use of introduced plants. Depending on the plant and its abundance, removing an introduced plant may impact honey bees more than wild pollinators.     

Bee Species Diversity Enhances Productivity and Stability in a Perennial Crop

Wild bees provide important pollination services to agroecoystems, but the mechanisms which underlie their contribution to ecosystem functioning—and, therefore, their importance in maintaining and enhancing these services—remain unclear. We evaluated several mechanisms through which wild bees contribute to crop productivity, the stability of pollinator visitation, and the efficiency of individual pollinators in a highly bee-pollination dependent plant, highbush blueberry. We surveyed the bee community (through transect sampling and pan trapping) and measured pollination of both open- and singly-visited flowers. We found that the abundance of managed honey bees, Apis mellifera, and wild-bee richness were equally important in describing resulting open pollination. Wild-bee richness was a better predictor of pollination than wild-bee abundance. We also found evidence suggesting pollinator visitation (and subsequent pollination) are stabilized through the differential response of bee taxa to weather (i.e., response diversity). Variation in the individual visit efficiency of A. mellifera and the southeastern blueberry bee, Habropoda laboriosa, a wild specialist, was not associated with changes in the pollinator community. Our findings add to a growing literature that diverse pollinator communities provide more stable and productive ecosystem services.     

Pollination efficiency and foraging behaviour of honey bees and non‐Apis bees to sweet cherry

1. Crop pollination generally increases with pollinator diversity and wild pollinator visitation. To optimize crop pollination, it is necessary to investigate the pollination contribution of different pollinator species. In the present study, we examined this contribution of honey bees and non‐Apis bees (bumble bees, mason bees and other solitary bees) in sweet cherry.
2. We assessed the pollination efficiency (fruit set of flowers receiving only one visit) and foraging behaviour (flower visitation rate, probability of tree change, probability of row change and contact with the stigma) of honey bees and different types of non‐Apis bees.
3. Single visit pollination efficiency on sweet cherry was higher for both mason bees and solitary bees compared with bumble bees and honey bees. The different measures of foraging behaviour were variable among non‐Apis bees and honey bees. Adding to their high single visit efficiency, mason bees also visited significantly more flower per minute, and they had a high probability of tree change and a high probability to contact the stigma.
4. The results of the present study highlight the higher pollination performance of solitary bees and especially mason bees compared with bumble bees and honey bees. Management to support species with high pollination efficiency and effective foraging behaviour will promote crop pollination.

     

Foraging at a safe distance: crab spider effects on pollinators

1. The ability of pollinating insects to discover and evade their predators can affect plant–pollinator mutualisms and have cascading ecosystem effects. Pollinators will avoid flowers with predators, but it is not clear how far away they will move to continue foraging. If these distances are relatively small, the impact of predators on the plant–pollinator mutualism may be lessened. The plant could continue to receive some pollination, and pollinators would reduce the time and energy needed to search for another patch. 2. A native crab spider, Xysticus elegans, was placed on one cluster in a small array of Baccharis pilularis inflorescence clusters, and the preferred short‐range foraging distances of naturally visiting pollinators was determined. 3. Nearly all pollinator taxa (honey bees, wasps, other Hymenoptera, and non‐bombyliid flies) spent less time foraging on the predator cluster. 4. The key result of this study is that inflorescences within 90 mm of the crab spider were avoided by visiting honey bees and wasps, which spent three‐ and 18‐fold more time, respectively, foraging on more distant flower clusters. 5. Whether honey bees can use olfaction to detect spiders was then tested, and this study provides the first demonstration that honey bees will avoid crab spider odour alone at a food source.     

Keystone resources available to wild pollinators in a winter‐flowering tree crop plantation

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Potential negative effects of exotic honey bees on the diversity of native pollinators and yield of highland coffee plantations

• 1 The honey bee Apis mellifera is native to Eurasia and Africa, although it is commonly introduced into crop fields of different parts of the world because of the assumption that it improves yield. This bee is, however, a poor pollinator of several crops compared with native insects. Indeed, honey bees can displace native pollinators and reduce their diversity. The present study evaluated the potential impacts of A. mellifera on the diversity of native pollinators of highland coffee (Coffea arabica) and its putative consequences for coffee production at the state of Veracruz, Mexico.
• 2 The abundance of A. mellifera and diversity of native pollinators were assessed during blooming at 12 shade coffee plantations and pollination experiments were conducted to determine the impacts of pollinators on coffee fruit production. Regression analyses were used to assess whether the abundance of honey bees was related to native pollinator diversity, and whether fruit production was influenced by both the diversity of pollinators and the abundance of A. mellifera.
• 3 Native pollinator diversity decreased as the number of honey bees increased. Furthermore, although coffee fruit production was positively related to the diversity of native pollinators, an increasing abundance of A. mellifera was correlated with a decrease in fruit production.
• 4 Highland shade coffee plantations are considered as reservoirs of the Mexican insect fauna. Thus, native pollinator diversity could be better preserved if beekeepers reduced the number of managed hives that they brought into plantations. This may also help to increase coffee yield by decreasing the putative negative effects of A. mellifera on native pollinators.

     

Native flowering shrubs promote beneficial insects in avocado orchards

1. Flower strips can promote and conserve beneficial insects in agroecosystems. Knowing which groups are favoured and which plant traits affect visitation rates by beneficial insects is important for the design of plant strips.
2. We established 21 Native Flower Strips (NFS) in avocado orchards in Central Chile. NFS contained 7–11 plant species, with variable corolla length and flowering period, to promote beneficial insects. We assessed flight activity of ladybirds (Coccinellidae) and bees (Apiformes) in sites adjacent to and far from NFS within avocado orchards. Additionally, we evaluated flower visitation for the main flower visitor groups (Apiformes, Lepidoptera, Diptera, and Coleoptera) to the plant species in NFS according to season and corolla length.
3. We found almost six times greater flight activity of coccinellids and bees in NFS than sites far from NFS within avocado orchards. Visitation rates of pollinator groups varied according to corolla length and season. Diptera, Coleoptera, and Lepidoptera consistently visited short corolla flowers. NFS were highly visited in summer and autumn, when avocados were not in bloom.
4. NFS in orchards should be encouraged by policymakers because they support beneficial insects that could deliver ecosystem services and contribute to local biological conservation.

     

Farming practices influence wild pollinator populations on squash and pumpkin

Recent declines in managed honey bee, Apis mellifera L., colonies have increased interest in the current and potential contribution of wild bee populations to the pollination of agricultural crops. Because wild bees often live in agricultural fields, their population density and contribution to crop pollination may be influenced by farming practices, especially those used to reduce the populations of other insects. We took a census of pollinators of squash and pumpkin at 25 farms in Virginia, West Virginia, and Maryland to see whether pollinator abundance was related to farming practices. The main pollinators were Peponapis pruinosa Say; honey bees, and bumble bees (Bombus spp.). The squash bee was the most abundant pollinator on squash and pumpkin, occurring at 23 of 25 farms in population densities that were commonly several times higher than that of other pollinators. Squash bee density was related to tillage practices: no-tillage farms hosted three times as great a density of squash bees as tilled farms. Pollinator density was not related to pesticide use. Honey bee density on squash and pumpkin was not related to the presence of managed honey bee colonies on farms. Farms with colonies did not have more honey bees per flower than farms that did not keep honey bees, probably reflecting the lack of affinity of honey bees for these crops. Future research should examine the economic impacts of managing farms in ways that promote pollinators, particularly pollinators of crops that are not well served by managed honey bee colonies.     

Pollination efficiency of wild bees and hoverflies provided to oilseed rape

• 1 Declining numbers in honeybees and various wild bee species pose a threat to global pollination services. The identification and quantification of the pollination service provided by different taxa within the pollinator guild is a prerequisite for the successful establishment of nature conservation and crop management regimes.
• 2 Wild bees and hoverflies are considered to be valuable pollinators in agricultural and natural systems. Although some information on pollination efficiency of individual pollinator species is available, comparative studies of both taxa at different densities are rare. In the present study, the efficiency of the solitary mason bee Osmia rufa and two hoverfly species (Eristalis tenax and Episyrphus balteatus) as pollinators of oilseed rape Brassica napus was examined in a standardized caged plant breeding regime. Honeybee Apis mellifera colonies were used as a reference pollinator taxon.
• 3 Yield parameters responded differently to pollinator density and identity. Fruit set and number of seeds per pod increased with increasing pollinator density, although these were stronger in the mason bee than the hoverfly treatment. Weight per 1000 seeds did not respond to any pollinator treatment, indicating that seed quality was not affected. Oilseed rape yield in the highest tested densities of both pollinator taxa resulted in yield values close to the efficiency of small honeybee colonies.
• 4 Hoverflies required approximately five‐fold densities of the red mason bees to reach a similar fruit set and yield. Thus, mason bees are more efficient in plant breeding and managed pollination systems. Both natural pollinator taxa, however, are of potential value in open and closed crop production systems.

     

Relationships between wild bees,hoverflies and pollination success in apple orchards with different landscape contexts

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Bee Preference for Native versus Exotic Plants in Restored Agricultural Hedgerows

Habitat restoration to promote wild pollinator populations is becoming increasingly common in agricultural lands. Yet, little is known about how wild bees, globally the most important wild pollinators, use resources in restored habitats. We compared bee use of native and exotic plants in two types of restored native plant hedgerows: mature hedgerows (>10 years from establishment) designed for natural enemy enhancement and new hedgerows (≤2 years from establishment) designed to enhance bee populations. Bees were collected from flowers using timed aerial netting and flowering plant cover was estimated by species using cover classes. At mature hedgerow sites, wild bee abundance, richness, and diversity were greater on native plants than exotic plants. At new sites, where native plants were small and had limited floral display, abundance of bees was greater on native plants than exotic plants; but, controlling for floral cover, there was no difference in bee diversity and richness between the two plant types. At both mature and new hedgerows, wild bees preferred to forage from native plants than exotic plants. Honey bees, which were from managed colonies, also preferred native plants at mature hedgerow sites but exhibited no preference at new sites. Our study shows that wild bees, and managed bees in some cases, prefer to forage on native plants in hedgerows over co‐occurring weedy, exotic plants. Semi‐quantitative ranking identified which native plants were most preferred. Hedgerow restoration with native plants may help enhance wild bee abundance and diversity, and maintain honey bee health, in agricultural areas.     

The Potential Influence of Bumble Bee Visitation on Foraging Behaviors and Assemblages of Honey Bees on Squash Flowers in Highland Agricultural Ecosystems

Bee species interactions can benefit plant pollination through synergistic effects and complementary effects, or can be of detriment to plant pollination through competition effects by reducing visitation by effective pollinators. Since specific bee interactions influence the foraging performance of bees on flowers, they also act as drivers to regulate the assemblage of flower visitors. We selected squash (Cucurbita pepo L.) and its pollinators as a model system to study the foraging response of honey bees to the occurrence of bumble bees at two types of sites surrounded by a high amount of natural habitats (≥ 58% of land cover) and a low amount of natural habitats (≤ 12% of land cover) in a highland agricultural ecosystem in China. At the individual level, we measured the elapsed time from the departure of prior pollinator(s) to the arrival of another pollinator, the selection of honey bees for flowers occupied by bumble bees, and the length of time used by honey bees to explore floral resources at the two types of sites. At the community level, we explored the effect of bumble bee visitation on the distribution patterns of honey bees on squash flowers. Conclusively, bumble bee visitation caused an increase in elapsed time before flowers were visited again by a honey bee, a behavioral avoidance by a newly-arriving honey bee to select flowers occupied by bumble bees, and a shortened length of time the honey bee takes to examine and collect floral resources. The number of overall bumble bees on squash flowers was the most important factor explaining the difference in the distribution patterns of honey bees at the community level. Furthermore, decline in the number of overall bumble bees on the squash flowers resulted in an increase in the number of overall honey bees. Therefore, our study suggests that bee interactions provide an opportunity to enhance the resilience of ecosystem pollination services against the decline in pollinator diversity.     

Hedgerows surrounding organic apple orchards in north‐west Spain: potential to conserve beneficial insects

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Exposure of the wild bee Osmia bicornis to the honey bee pathogen Nosema ceranae

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Managed bumble bees increase flower visitation but not fruit weight in polytunnel strawberry crops

Animal-mediated pollination is essential for the production and quality of fruits and seeds of many crops consumed by humans. However, crop pollination services might be compromised when wild pollinators are scarce. Managed pollinators are commonly used in crops to supplement such services with the assumption that they will enhance crop yield. However, information on the spatiotemporal pollinator-dependence of crops is still limited. We assessed the contribution of commercial bumble bee colonies compared to the available pollinator community on strawberry (‘Fortuna’ variety) flower visitation and strawberry quality across a landscape gradient of agricultural intensification (i.e. polytunnel berry crop cover). We used colonies of bumble bees in winter and in spring, i.e. when few and most wild pollinators are in their flight period, respectively. The placement of colonies increased visits of bumble bees to strawberry flowers, especially in winter. The use of bumble bee colonies did not affect flower visitation by other insects, mainly honey bees, hoverflies and other Diptera. Flower visitation by both honey bees and wild insects did not vary between seasons and was unrelated to the landscape gradient of berry crop cover. Strawberries were of the highest quality (i.e. weight) when insect-mediated pollination was allowed, and their quality was positively related to wild flower visitors in winter but not in spring. However, increased visits to strawberry flowers by managed bumble bees and honey bees had no effect on strawberry weight. Our results suggest that the pollination services producing high quality strawberry fruits are provided by the flower visitor community present in the study region without the need to use managed bumble bees.     

Farmland in U.S. Conservation Reserve Program has unique floral composition that promotes bee summer foraging

Bee conservation is a topic of global concern, particularly in agroecosystems where their contribution to crop pollination is highly valued. Over a decade ago, bees and other pollinators were made a priority of the Conservation Reserve Program (CRP), a U.S. federal program that pays land owners to establish a conservation cover, typically grassland, on environmentally sensitive farmland. Despite large financial investment in this program, few studies have measured the benefit of CRP to bees, particularly in complex agroecosystems with abundant alternative forage. To determine if CRP land seeded with pollinator-attractive native flowers and/or introduced legumes provides distinct floral composition that attracts more foraging bees than non-CRP habitats, we compared CRP land to paired non-CRP fields and roadsides at 31 sites in Michigan, U.S.A.. We found CRP land had unique floral species community composition, higher floral abundance, greater species richness, more native floral species, and greater inflorescence coverage. Greater inflorescence coverage on CRP land was associated with a greater abundance of both honey bees and wild bees than either non-CRP fields or roadsides, as was native flower abundance for wild bees. Showy native plant species were important forage resources on CRP land: Monarda fistulosa was the most foraged upon species by both honey bees and wild bees, and goldenrod species were important late-summer forage resources for honey bees. These findings demonstrate the benefit of managing CRP land with herbaceous seed mixes to create dense, showy, native plant communities that provide summer-long resources to both bee groups. Insights from this study could be used to enhance the composition of future conservation program investments and management of non-CRP land to benefit pollinators.     

Habitat loss and degradation due to farming intensification modify the floral visitor assemblages of a semiarid keystone shrub

1. The expansion of intensive agriculture has severely altered landscapes, a process that has been aggravated by the increase of greenhouse agriculture. However, few studies have considered the combined effects of habitat loss/degradation and greenhouse farming on insect visitors to native plants.
2. We analysed how habitat loss/degradation and greenhouse farming are related to the composition, abundance, and richness of the insect assemblages visiting flowers in a semiarid keystone shrub (Ziziphus lotus) in southeast Spain, home to Europe's largest area of greenhouses. We studied 21 populations distributed across a gradient of greenhouse intensification and habitat loss.
3. The composition, abundance, and richness of the Ziziphus insect assemblage substantially varied between populations and were differently affected by natural habitat-remnant and landscape degradation and population isolation.
4. Insect abundance was negatively affected by habitat loss at population level but positively affected at individual Ziziphus scale. Honey-bee relative abundance increased in highly degraded landscapes and isolated populations, being positively associated with hoverflies and negatively with ants and bee-flies. Wild bees, carrion flies, and wasps remain neutral along the degradation axes. Insect visitor abundance per plant affected positively the flower visitation rate, which was also favoured by the relative abundance of honey bees, wild bees, and hoverflies. Species richness was not influenced by anthropogenic degradation, and did not affect flower visitation rate.
5. Our results highlight the fragility of wild pollinator communities to landscape and habitat degradation, and the need to regulate intensive farming practices to preserve wild insect pollinator assemblages in semiarid habitats.

     

Biodiversity buffers pollination from changes in environmental conditions

A hypothesized underlying principle of the diversity‐functioning relationship is that functional groups respond differently to environmental change. Over 3 years, we investigated how pollinator diversity contributes to the magnitude of pollination service through spatial complementarity and differential response to high winds in California almond orchards. We found honey bees preferentially visited the top sections of the tree. Where wild pollinators were present, they showed spatial complementarity to honey bees and visited the bottom tree sections more frequently. As wind speed increased, honey bees' spatial preference shifted toward the bottom tree sections. In high winds (>2.5 m s^?1), orchards with low pollinator diversity (honey bees only) received almost no flower visits. In orchards with high pollinator diversity, visitation decreased to a lesser extent as wild bee visitation was unaffected by high winds. Our results demonstrate how spatial complementarity in diverse communities can help buffer pollination services to environmental changes like wind speed.     

Native bees buffer the negative impact of climate warming on honey bee pollination of watermelon crops

If climate change affects pollinator‐dependent crop production, this will have important implications for global food security because insect pollinators contribute to production for 75% of the leading global food crops. We investigate whether climate warming could result in indirect impacts upon crop pollination services via an overlooked mechanism, namely temperature‐induced shifts in the diurnal activity patterns of pollinators. Using a large data set on bee pollination of watermelon crops, we predict how pollination services might change under various climate change scenarios. Our results show that under the most extreme IPCC scenario (A1F1), pollination services by managed honey bees are expected to decline by 14.5%, whereas pollination services provided by most native, wild taxa are predicted to increase, resulting in an estimated aggregate change in pollination services of +4.5% by 2099. We demonstrate the importance of native biodiversity in buffering the impacts of climate change, because crop pollination services would decline more steeply without the native, wild pollinators. More generally, our study provides an important example of how biodiversity can stabilize ecosystem services against environmental change.     

Characterization of wild bee communities in apple and blueberry orchards

1. Wild bees provide invaluable ecosystem services in agricultural landscapes such as pollination. However, in recent decades, pollinator biodiversity, especially in wild bees, is declining on a global scale, with potentially far‐reaching consequences for crop production. Thus, there is an urgent need to determine whether wild bees are present in agricultural systems, such as fruit orchards.
2. In the present study, we examined the wild bee fauna at species and community levels during the period of bee activity (May to August) in apple and high‐bush blueberry orchards in New England.
3. Bee communities are crop‐specific and dominated by very few species, which fluctuate according to crop and season. The blueberry associated bee fauna was more diverse. In apple, communities were phylogenetically clustered at the genus level and dominated by solitary ground nesting bees within the genus Andrena. Species fluctuated widely in presence and abundance throughout the season, leading to differences in community composition and functional trait structure.
4. The results obtained in the present study show that apple and blueberry harbour a distinct and diverse bee fauna that performs vital pollination services in orchards. Our results provide essential baseline data for wild bees in blueberry and apple orchards and this can be used to improve management and conservation strategies for wild bee preservation in these crops.