Watermelon pollinators exhibit complementarity in both visitation rate and single-visit pollination efficiency

Insect-Mediated Pollination of Strawberries in an Urban Environment

Pollination services provided by a diversity of pollinators are critical in agriculture because they enhance the yield of many crops. However, few studies have assessed pollination services in urban agricultural systems. We performed flower-visitor observations and pollination experiments on strawberries (Fragaria × ananassa) in an urban area near Paris, France, in order to assess the effects of (i) insect-mediated pollination service and (ii) potential pollination deficit on fruit set, seed set, and fruit quality (size, weight, and malformation). Flower-visitor observations revealed that the pollinator community solely comprised unmanaged pollinators, despite the presence of beehives in the surrounding landscape. Based on the pollination experiments, we found that the pollination service mediated by wild insects improved the fruit size as a qualitative value of production, but not the fruit set. We also found no evidence of pollination deficit in our urban environment. These results suggest that the local community of wild urban pollinators is able to support strawberry crop production and thus plays an important role in providing high-quality, local, and sustainable crops in urban areas.

Effects of Managed and Unmanaged Floral Margins on Pollination Services and Production in Melon Crops

Melon is among the most consumed fruits in the world, being a crop that depends almost entirely on insects for its reproduction, which is why it is especially sensitive to declining pollination services. Restoration and maintenance of hedgerows and agricultural borders around crops are generally carried out by sowing flowering herbaceous plants or establishing shrubby species; however, a cost-effective and lower-maintenance alternative for farmers could be as simple as allowing vegetation to regenerate naturally without any management actions. This work aimed to test the effects of three different types of margins (managed herbaceous, managed shrubby, and unmanaged herbaceous) on the overall abundance and richness of wild pollinators in melon crops. The work was performed in three localities in southern Spain over two years. Pollinators were monitored visually using 1 × 1 m sampling squares and pan traps within melon fields. Moreover, crop yield was estimated by measuring fruit weight and the number of seeds. In general, higher abundances of pollinators were observed in melon fields during the second year. In addition, the abundances of Syrphidae, Andrenidae, Apidae (excl. Apis mellifera), and pollinators other than bees, belonging to the orders Diptera, Coleoptera, Hymenoptera, and Lepidoptera, showed higher values in melon fields with shrubby margins than in fields with herbaceous margins (managed or unmanaged). However, no effect of floral margins on the yield of melon crops was found.

The Role of Uncultivated Habitats in Supporting Wild Bee Communities in Mediterranean Agricultural Landscapes

In agricultural landscapes, uncultivated habitat patches may have a focal role in supporting communities of ecosystem service providers. However, little is known on the variances among different types of uncultivated habitat patches in providing resources and maintaining populations of these beneficial organisms. We studied wild bee communities in natural and semi-natural uncultivated patches embedded in semi-arid Mediterranean agricultural landscapes. We investigated the effects of local- and landscape-scale land-use characteristics, as well as their interactions, on bee diversity, functional composition, and forage and nesting resources. Most bee community parameters were affected by both local- and landscape-scale characteristics, but no significant interactions were found among the scales. Local land-use effects were related primarily to overall plant cover, and to the abundance and richness of flowering plants. Landscape effects, mostly limited to a 400 m range, were varied. The abundance of focal crop pollinators varied considerably between patch type and pollinator species. The different types of uncultivated habitats maintain complementary bee and flower communities. Our findings show the important role of uncultivated habitat patches in providing floral and nesting resources for bees, and creating resource-landscapes that can support wild bee communities and crop pollination services in Mediterranean agricultural landscapes.

Prioritizing pollinators over pests: wild bees are more important than beetle damage for watermelon yield

Insect pests and pollinators can interact directly and indirectly to affect crop production; however, impacts of these interactions on marketable yield are little known. Thus, the evaluation of interactions between pests and pollinators are needed to best prioritize management efforts. Over 2 years, we evaluated the impact of pollinator visitation and/or beetle (Acalymma vittatum) infestation on fruit set and yield in seedless watermelon production. In 2020, we tested the main effect of pollinator visitation: two or eight honeybee visits, two wild bee visits, hand pollinated and open pollinated. In 2021, we crossed wild and managed pollinator visitation (two or four honeybee visits, two or four wild bee visits, hand pollinated and open pollinated) with varying beetle infestation levels (0, 3, 6 and 9 beetles/plant). In both years, wild bees contributed significantly to high fruit yields, and exclusive visitation from wild bees increased yield by a factor of 1.5-3 compared to honeybees. In 2021, pollination was the only significant factor for fruit set and marketable yield even when compared to the varying beetle infestation levels. These data advocate for a reprioritization of management, to conserve and protect wild bee pollination, which could be more critical than avoiding pest damage for ensuring high yields.

Pollination Effectiveness of the Hoverfly Eristalinus aeneus (Scopoli, 1763) in Diploid and Triploid Associated Watermelon Crop

Watermelon (Citrullus lanatus) is an important crop worldwide. Pollination of this crop is carried out by insects, with honey bees (Apis spp.) and bumble bees (Bombus spp.) as the most used in greenhouse production. Nevertheless, due to the extreme conditions in closed enclosures, these hymenopterans suffer management and behavior problems leading to insufficient pollination. The effectiveness of three release densities (15, 30, and 45 individuals/m²) of Eristalinus aeneus was compared in diploid- and triploid-associated watermelon varieties under protected cultivation. Floral visits, pollen-pistil interaction after pollen transport, yield, and fruit quality were evaluated. The number of floral visits increased with release density in both pistillate and staminate flowers. No significant differences were observed, however, among release densities or between flower types in the duration of the visits. Floral preferences were not found in the behavior of E. aeneus in watermelon. High and medium release densities increased pollen deposition onto the stigma, and consequently the yield of the triploid variety compared to low release density, by 23.8 to 41.8% in 2020 and by 36.3 to 46.7% in 2021. The results of this trial demonstrate the potential of E. aeneus as a managed pollinator in protected cultivation of triploid watermelon.

Local diversification enhances pollinator visitation to strawberry and may improve pollination and marketability

Numerous studies show that semi-natural habitats within agricultural landscapes benefit native pollinating insects and increase resultant crop pollination services. More recently, evidence is emerging that agricultural diversification techniques on farms, as well as increased compositional and configurational heterogeneity within the cropped portion of landscapes, enhance pollinator communities. However, to date, only a few studies have investigated how diversifying the crops within the farm field itself (i.e., polyculture) influences wild pollinator communities and crop pollination services. In the Central Coast of California, we investigate how local crop diversification within fields, crossed with the proportion of natural habitat in the surrounding landscape, jointly affect pollinator communities and services to strawberry. On 16 organic farms varying in farm type (monoculture vs. polyculture) and proportion of natural land cover, we find that both factors enhance pollinator abundance and richness, although neither affect honey bee abundance. Further, natural cover has a stronger effect on pollinator richness on monoculture (vs. polyculture) farms. Although strawberry can self-pollinate, we document experimentally that pollinator exclusion doubles the probability of berry malformation, while excluding both pollinators and wind triples malformation, with corresponding effects on berry marketability. Finally, in post-hoc tests, we find that berry malformation is significantly higher with greater visitation by honey bees, and observed a trend that this reduction was mitigated by increased native bee richness. These results suggest that both polyculture and semi-natural habitat cover support more abundant and diverse pollinator communities, and that ambient levels of pollinator visitation to strawberry provide an important crop pollination service by improving berry marketability (i.e., by reducing berry malformation). Although further confirmation would be needed, our work suggests that honey bees alone do not provide sufficient pollination services. Prior work has shown that honey bees tend to visit only the top of the strawberry flower receptacle, while other native bees often crawl around the flower base, leading to more complete pollination of the achenes and, consequently, better formed berries. If honey bee visits reduced native bee visitation in our system, this could explain the unexpected correlation between increased honey bee visits and malformation.

The effects of pollinator diversity on pollination function

Pollination is a key ecological function of most terrestrial ecosystems. Decades of research on single-trophic-level communities, particularly plant communities, have helped build the foundation of diversity-function theory. Yet as it stands, this theory appears to be less useful for inter-trophic-level functions such as pollination, as evidenced by empirical findings that are often inconsistent with theoretical expectations. In this review, we evaluate how canonical diversity-function theory has been applied to pollination function, focusing on empirical studies of the mechanisms that drive pollinator diversity-function relationships. We first identify key features of pollination function that have hampered reconciliation with current theory. We then examine terminology for mechanisms used to discuss the findings from pollinator diversity-function studies that are sometimes inconsistent with established ecological concepts. We propose a revised diversity-function framework and describe two non-canonical diversity-function mechanisms that are particularly applicable to pollination. The first, 'interactive functional complementarity', was identified previously but remains overlooked. The second, a new diversity-function mechanism, 'functional enhancement', occurs when pollinator diversity increases within-niche activity. Finally, we discuss experimental approaches necessary to detect diversity-function effects in pollination. This article is protected by copyright. All rights reserved.

Complementary Contribution of Wild Bumblebees and Managed Honeybee to the Pollination Niche of an Introduced Blueberry Crop

The entomophilous pollination niche (abundance, phenotypic traits, foraging behaviours and environmental tolerances of insect pollinators) helps to understand and better manage crop pollination. We apply this niche approach to assess how an entomophilous crop (blueberry, Vaccinium ashei) can be expanded into new territories (i.e., northern Spain) far from their original area of domestication (North America). Insect visits to blueberry flowers were monitored in a plantation on 12 different days, at 8 different times during day and covering various weather conditions. Abundance, visitation rate, pollen gathering behaviour, and frequency of inter-plant and inter-row movements were recorded. The pollinator assemblage was basically composed of one managed honeybee species (50.8% of visits) and three native bumblebee species (48.3%). There was a marked pattern of seasonal segregation throughout bloom, with bumblebees dominating the early bloom and honeybee the late bloom. Pollinators also segregated along gradients of daily temperature and relative humidity. Finally, the two pollinator types differed in foraging behaviour, with bumblebees having a visitation rate double that of honeybee, collecting pollen more frequently and changing plant and row more frequently. The spatio-temporal and functional complementarity between honeybee and bumblebees suggested here encourages the consideration of an integrated crop pollination strategy for blueberries, based on the concurrence of both wild and managed bees.

Pollination in Agroecosystems: A Review of the Conceptual Framework with a View to Sound Monitoring

The pollination ecology in agroecosystems tackles a landscape in which plants and pollinators need to adjust, or be adjusted, to human intervention. A valid, widely applied approach is to regard pollination as a link between specific plants and their pollinators. However, recent evidence has added landscape features for a wider ecological perspective. Are we going in the right direction? Are existing methods providing pollinator monitoring tools suitable for understanding agroecosystems? In Italy, we needed to address these questions to respond to government pressure to implement pollinator monitoring in agroecosystems. We therefore surveyed the literature, grouped methods and findings, and evaluated approaches. We selected studies that may contain directions and tools directly linked to pollinators and agroecosystems. Our analysis revealed four main paths that must come together at some point: (i) the research question perspective, (ii) the advances of landscape analysis, (iii) the role of vegetation, and (iv) the gaps in our knowledge of pollinators taxonomy and behavior. An important conclusion is that the pollinator scale is alarmingly disregarded. Debate continues about what features to include in pollinator monitoring and the appropriate level of detail: we suggest that the pollinator scale should be the main driver.

Metatranscriptome Analysis of Sympatric Bee Species Identifies Bee Virus Variants and a New Virus, Andrena-Associated Bee Virus-1

Bees are important plant pollinators in agricultural and natural ecosystems. High average annual losses of honey bee (Apis mellifera) colonies in some parts of the world, and regional population declines of some mining bee species (Andrena spp.), are attributed to multiple factors including habitat loss, lack of quality forage, insecticide exposure, and pathogens, including viruses. While research has primarily focused on viruses in honey bees, many of these viruses have a broad host range. It is therefore important to apply a community level approach in studying the epidemiology of bee viruses. We utilized high-throughput sequencing to evaluate viral diversity and viral sharing in sympatric, co-foraging bees in the context of habitat type. Variants of four common viruses (i.e., black queen cell virus, deformed wing virus, Lake Sinai virus 2, and Lake Sinai virus NE) were identified in honey bee and mining bee samples, and the high degree of nucleotide identity in the virus consensus sequences obtained from both taxa indicates virus sharing. We discovered a unique bipartite + ssRNA Tombo-like virus, Andrena-associated bee virus-1 (AnBV-1). AnBV-1 infects mining bees, honey bees, and primary honey bee pupal cells maintained in culture. AnBV-1 prevalence and abundance was greater in mining bees than in honey bees. Statistical modeling that examined the roles of ecological factors, including floral diversity and abundance, indicated that AnBV-1 infection prevalence in honey bees was greater in habitats with low floral diversity and abundance, and that interspecific virus transmission is strongly modulated by the floral community in the habitat. These results suggest that land management strategies that aim to enhance floral diversity and abundance may reduce AnBV-1 spread between co-foraging bees.

National scale mapping of ecosystem services in Israel – genetic resources, pollination and cultural services

The Israel - National Ecosystem Assessment (I-NEA) project aims to present a comprehensive picture of the state and trends of Israel's ecosystem services across all ecosystems, by integrating existing data and information collected from a wide range of sources. Although there is a lack of information about the spatial distribution of ecosystem services’ provisioning in Israel, their mapping constitutes an important part of the assessment.

In this paper, we present a national-scale mapping of three ecosystem services, each of them implemented using different methods: 1) Genetic resources service, mapped using spatial observations of the Crop Wild Relatives species; 2) potential of pollination service, which is provided by wild bees, mapped using an expert-based habitat model related to land use and land cover; and 3) cultural service of recreation, mapped by analysing the distribution of geotagged digital photographs uploaded to social media resources. The derived maps visualise, for the first time in Israel, the spatially distributed values of the three ecosystem services. Supply hotspots with high values for all three services were identified, as well as spatial differences amongst the ecosystem services. These national-scale maps provide overlooked insights and can be very useful for strategic discussions of stakeholders and decision-makers but should be regarded with caution given existing knowledge gaps and possible inaccuracies due to data scarcity and low resolution.

Examination of a Managed Pollinator Strategy for Almond Production Using Apis mellifera (Hymenoptera: Apidae) and Osmia lignaria (Hymenoptera: Megachilidae)

Pollination services provided by managed bees are essential for California almond (Prunus dulcis Mill.; Rosales: Rosaceae) production. Currently, pollination needs are met by rented or owned Apis mellifera L. (Hymenoptera: Apidae; honey bee) colonies. Excessive demand on a challenged A. mellifera industry to provide strong colonies in early spring has caused sharp increases in rental prices over the past decade, inviting the consideration of alternative pollinators in addition to, or in place of, A. mellifera. Osmia lignaria Say (Hymenoptera: Megachilidae; the blue orchard bee) is an excellent pollinator of fruit and nut trees, but its pollination impacts when used in tandem with A. mellifera have yet to be evaluated in commercial almond orchards. A 2-yr study was conducted in California orchards to compare almond pollination and production using A. mellifera as sole pollinator to an alternative practice of adding O. lignaria as a co-pollinator with A. mellifera. Almond orchard managerial decisions, such as for pesticide use and irrigation intensity, vary between almond growing regions because of local climates. Therefore, both north-central and southern sites of California's San Joaquin Valley are represented. We compared bee visitation, nut set, and nut yield between orchards and between tree rows within orchards. Also, O. lignaria reproductive success was recorded to assure that these bees remained in the orchards as pollinators and to assess the ability to sustain these bees under regional orchard conditions. We demonstrated that augmenting large commercial almond orchards with O. lignaria can significantly increase nut set and sometimes nut yield in both regions evaluated.

Using niche breadth theory to explain generalization in mutualisms

For a mutualism to remain evolutionarily stable, theory predicts that mutualists should limit their associations to high-quality partners. However, most mutualists either simultaneously or sequentially associate with multiple partners that confer the same type of reward. By viewing mutualisms through the lens of niche breadth evolution, we outline how the environment shapes partner availability and relative quality, and ultimately a focal mutualist's partner breadth. We argue that mutualists that associate with multiple partners may have a selective advantage compared to specialists for many reasons, including sampling, complementarity, and portfolio effects, as well as the possibility that broad partner breadth increases breadth along other niche axes. Furthermore, selection for narrow partner breadth is unlikely to be strong when the environment erodes variation in partner quality, reduces the costs of interacting with low-quality partners, spatially structures partner communities, or decreases the strength of mutualism. Thus, we should not be surprised that most mutualists have broad partner breadth, even if it allows for ineffective partners to persist.

Florally rich habitats reduce insect pollination and the reproductive success of isolated plants

Landscape heterogeneity in floral communities has the potential to modify pollinator behavior. Pollinator foraging varies with the diversity, abundance, and spatial configuration of floral resources. However, the implications of this variation for pollen transfer and ultimately the reproductive success of insect pollinated plants remains unclear, especially for species which are rare or isolated in the landscape. We used a landscape-scale experiment, coupled with microsatellite genotyping, to explore how the floral richness of habitats affected pollinator behavior and pollination effectiveness. Small arrays of the partially self-compatible plant Californian poppy (Eschscholzia californica) were introduced across a landscape gradient to simulate rare, spatially isolated populations. The effects on pollinator activity, outcrossing, and plant reproduction were measured. In florally rich habitats, we found reduced pollen movement between plants, leading to fewer long-distance pollination events, lower plant outcrossing, and a higher incidence of pollen limitation. This pattern indicates a potential reduction in per capita pollinator visitation, as suggested by the lower activity densities and richness of pollinators observed within florally rich habitats. In addition, seed production reduced by a factor of 1.8 in plants within florally rich habitats and progeny germination reduced by a factor of 1.2. We show this to be a consequence of self-fertilization within the partially self-compatible plant, E. californica. These findings indicate that locally rare plants are at a competitive disadvantage within florally rich habitats because neighboring plant species disrupt conspecific mating by co-opting pollinators. Ultimately, this Allee effect may play an important role in determining the long-term persistence of rarer plants in the landscape, both in terms of seed production and viability. Community context therefore requires consideration when designing and implementing conservation management for plants which are comparatively rare in the landscape.

How Efficient Is Apis cerana (Hymenoptera: Apidae) in Pollinating Cabbage, Brassica oleracea var. capitata? Pollination Behavior, Pollinator Effectiveness, Pollinator Requirement, and Impact of Pollination

Cabbage is a cross-pollinated crop because of sporophytic self-incompatibility, and honey bees play an important role in its pollination. Though Asian honey bees, Apis cerana F., are used in pollination of cabbage, the rate of visitation, behavior, pollinator efficacy, and impact on seed-set are to be determined. Apis cerana occupy a share of 19.18% of all the flower visitors of cabbage in natural habitat of North Western Indian Himalayas. Pollination behavior in terms of peak activity, flowers processed per unit time, time spent per flower, and time spent in search of flowers are studied separately for both pollen and nectar foragers. Pollinator effectiveness as measured by seed set in flowers excluded from bee visitation, single bee visit, and unrestricted pollinator visits was 0.11. Studies on the impact of A. cerana bee pollination in cabbage seed production revealed an increase of 17.28% in siliqua per panicle, with 26.11% increase in seed yield. For assessing the requirement of A. cerana to pollinate one hectare of cabbage, flower availability and the speed with which the pollen and nectar foragers process the flowers are taken into consideration. A forager is estimated to pollinate 4,780 flowers a day, but cabbage flower requires 9.09 visits of A. cerana for optimum seed set. Thus, a maximum of 4,999 bee foragers or 8.33 colonies are needed to effectively pollinate 1 ha of cabbage. Though A. cerana is a good pollinator, our findings suggest that it is not an ideal pollinator of cabbage.