Pollinator nutrition and its role in merging the dual objectives of pollinator health and optimal crop production

Bee and non-bee insect pollinators play an integral role in the quantity and quality of production for many food crops, yet there is growing evidence that nutritional challenges to pollinators in agricultural landscapes are an important factor in the reduction of pollinator populations worldwide. Schemes to enhance crop pollinator health have historically focused on floral resource plantings aimed at increasing pollinator abundance and diversity by providing more foraging opportunities for bees. These efforts have demonstrated that improvements in bee diversity and abundance are achievable; however, goals of increasing crop pollination outcomes via these interventions are not consistently met. To support pollinator health and crop pollination outcomes in tandem, habitat enhancements must be tailored to meet the life-history needs of specific crop pollinators, including non-bees. This will require greater understanding of the nutritional demands of these taxa together with the supply of floral and non-floral food resources and how these interact in cropping environments. Understanding the mechanisms underlying crop pollination and pollinator health in unison across a range of taxa is clearly a win–win for industry and conservation, yet achievement of these goals will require new knowledge and novel, targeted methods.
 
 This article is part of the theme issue ‘Natural processes influencing pollinator health: from chemistry to landscapes’

Network modularity influences plant reproduction in a mosaic tropical agroecosystem

Biodiversity influences ecosystem function, but there is limited understanding of the mechanisms that support this relationship across different land use types in mosaic agroecosystems. Network approaches can help to understand how community structure influences ecosystem function across landscapes; however, in ecology, network analyses have largely focused on species–species interactions. Here, we use bipartite network analysis in a novel way: to link pollinator communities to sites in a tropical agricultural landscape. We used sentinel plants of Brassica rapa to examine how the structure of the community network influences plant reproduction. Diptera was the most common order of flower visitors at every site. Syrphidae visits were the strongest contributor to the number of fertilized pods, while visits by Syrphidae, Hymenoptera and Lepidoptera had the strongest effect on the number of seeds per pod. Sentinel pots at forest sites were visited by more unique species (i.e. species with higher d′) than sites in other land uses, and dairy sites had more visitors that were common across the network. Participation coefficients, which indicate how connected a single node is across network modules, were strong predictors of ecosystem function: plant reproduction increased at sites with higher participation coefficients. Flower visitor taxa with higher participation coefficients also had the strongest effect on plant reproduction. Hymenoptera visits were the best predictor for participation coefficients but an Allograpta sp. (Diptera: Syrphidae) was the most influential flower visitor species in the landscape network. A diverse insect community contributed to plant reproduction and connection among nodes in this system. Identifying the ‘keystone’ flower visitor species and sites that have a strong influence on network structure is a significant step forward to inform conservation priorities and decision-making in diverse agroecosystems

A new, practicable and economical cage design for experimental studies on small honey bee colonies

Bees are in decline globally as a result of multiple stressors including pests, pathogens and contaminants. The management of bees in enclosures can identify causes of decline under standardized conditions but the logistics of conducting effect studies in typical systems used across several colonies is complex and costly. This study details a practicable, new and economical cage system that effectively houses live honey bee colonies to investigate the impact of physical conditions, biological factors and environmental contaminants on honey bee health. The method has broad application for a range of effect studies concerning honey bee development, physiology, survival and population dynamics because it enables entire colonies, as opposed to individual workers, to be managed well in captivity

Prey removal in cotton crops next to woodland reveals periodic diurnal and nocturnal invertebrate predation gradients from the crop edge by birds and bats

Factors influencing the efficacy of insectivorous vertebrates in providing natural pest control services inside crops at increasing distances from the crop edge are poorly understood. We investigated the identity of vertebrate predators (birds and bats) and removal of sentinel prey (mealworms and beetles) from experimental feeding trays in cotton crops using prey removal trials, camera traps and observations. More prey was removed during the day than at night, but prey removal was variable at the crop edge and dependent on the month (reflecting crop growth and cover) and time of day. Overall, the predation of mealworms and beetles was 1-times and 13-times greater during the day than night, respectively, with predation on mealworms 3-5 times greater during the day than night at the crop edge compared to 95 m inside the crop. Camera traps identified many insectivorous birds and bats over crops near the feeding trays, but there was no evidence of bats or small passerines removing experimental prey. A predation gradient from the crop edge was evident, but only in some months. This corresponded to the foraging preferences of open-space generalist predators (magpies) in low crop cover versus the shrubby habitat preferred by small passerines, likely facilitating foraging away from the crop edge later in the season. Our results are in line with Optimal Foraging Theory and suggest that predators trade-off foraging behaviour with predation risk at different distances from the crop edge and levels of crop cover. Understanding the optimal farm configuration to support insectivorous bird and bat populations can assist farmers to make informed decisions regarding in-crop natural pest control and maximise the predation services provided by farm biodiversity

The role of flies as pollinators of horticultural crops : an Australian case study with worldwide relevance

Australian horticulture relies heavily on the introduced managed honey bee, Apis mellifera Linnaeus 1758 (Hymenoptera: Apidae), to pollinate crops. Given the risks associated with reliance upon a single species, it would be prudent to identify other taxa that could be managed to provide crop pollination services. We reviewed the literature relating to the distribution, efficiency and management potential of a number of flies (Diptera) known to visit pollinator-dependent crops in Australia and worldwide. Applying this information, we identified the taxa most suitable to play a greater role as managed pollinators in Australian crops. Of the taxa reviewed, flower visitation by representatives from the dipteran families Calliphoridae, Rhiniidae and Syrphidae was frequently reported in the literature. While data available are limited, there was clear evidence of pollination by these flies in a range of crops. A review of fly morphology, foraging behaviour and physiology revealed considerable potential for their development as managed pollinators, either alone or to augment honey bee services. Considering existing pollination evidence, along with the distribution, morphology, behaviour and life history traits of introduced and endemic species, 11 calliphorid, two rhiniid and seven syrphid species were identified as candidates with high potential for use in Australian managed pollination services. Research directions for the comprehensive assessment of the pollination abilities of the identified taxa to facilitate their development as a pollination service are described. This triage approach to identifying species with high potential to become significant managed pollinators at local or regional levels is clearly widely applicable to other countries and taxa

Interaction-site networks identify interactions for conserving key pollinators and plants in an agricultural mosaic landscape

Pollinators utilize different land-uses via the plants they visit, however these connections vary within and among land-uses. Identifying which insects are carrying pollen and from where can elucidate key plant-pollinator interactions and identify the most important sites for maintaining community-level interactions in different land-use types. We developed a novel interaction-site bipartite network approach to identify which land-use types at the field- and landscape-scale best conserve plant-pollinator interactions. We identified distinct pollen-insect interactions that were highly specialised to both natural and modified land-uses. Many interactions involved flies, wasps and beetles; groups requiring greater research effort. Field-scale land-use best predicted interaction richness, uniqueness and strength. Management at this scale may provide the best outcomes for conserving or restoring plant-pollinator interactions in modified landscapes. This novel, intuitive approach could inform land-use planning, whereby priority is afforded to conservation areas that represent significant links between plant and pollinator communities within mosaic landscapes

The missing links: Bee and non-bee alpine visitor observation networks differ to pollen transport networks

1. A majority of the world’s flowering plants benefit from insect pollination. Bees in particular are known to carry large amounts of pollen, and the pollen load transported is often highly conspecific. However, there is limited knowledge about the transfer of pollen by other non-bee flower-visiting insect taxa. 2. We observed and collected insects visiting flowers in an Australian alpine plant community. We identified insect body pollen loads to evaluate the relative differences among taxa using visitation and pollen transport networks. We sampled a diverse pollinator community from 39 insect families that visited 31 plant species (n = 488 individual insects). 3. Pollen abundance and richness on insect bodies varied significantly among Diptera, Hymenoptera and Lepidoptera both among individuals and across insect families. 4. Bees carried more pollen overall than the other three insect orders surveyed, yet dipterans were the most frequent flower visitors overall, with six dipteran families observed visiting flowers more frequently than the most frequent hymenopteran visitor (Apis mellifera L.). Apidae was also the only family in this study to carry consistently large quantities of pollen. 5. At the order level, Diptera carried the second highest quantity of pollen but greater diversity of pollen than other insect orders. Importantly, visitation networks revealed visits to plant taxa that were not identified in pollen transport networks and vice versa. 6. Given the missing links in both visitor observation and pollen transfer networks, we advocate combining both types of networks to provide a more accurate estimate of the full range of plant–pollinator interactions occurring within and across taxa at the community level. Understanding the variation in plant–pollinator interactions as a result of differences among taxa and between networks of flower visitors, pollen transfer is important to evaluate the level of generalisation/specialisation among plants and their pollinator partners

Implications of grazing management systems incorporating planned rest for biodiversity conservation and landscape function in rangelands

Livestock grazing is recognised as a major driver of biodiversity decline and land degradation in rangelands around the globe. Protected areas alone cannot conserve global biodiversity, and therefore off-reserve conservation is necessary to achieve biodiversity conservation outside reserves and improve connectivity between reserves. Grazing management strategies that promote both ecological and production outcomes have the potential to conserve biodiversity and maintain or improve landscape function in agricultural landscapes. However, there is a lack of understanding of the response of biodiversity and landscape function to different grazing management systems in arid and semi-arid rangelands. This thesis explored the effects of commercial grazing practices that incorporate frequent periods of rest from grazing on biodiversity and landscape function, and determined the potential for using these alternative grazing practices to achieve broad-scale conservation outcomes. A systematic review and meta-analyses of scientific literature comparing grazing management incorporating periods of planned rest (strategic-rest grazing, SRG) with continuously grazed (CG) and ungrazed (UG) systems was undertaken to determine the effect of SRG on ecological and animal production variables. Where significant differences occurred, the trend analysis of ecological and animal production responses to grazing management predominantly favoured SRG over CG, except for animal weight gain, and favoured SRG over UG systems for plant, mammal and bird richness and diversity, but not invertebrate richness and diversity, biomass and ground cover. Most studies that compared plant species composition reported differences in response to grazing management. While we did not find any differences overall between grazing contrasts, meta-analyses of plant richness, diversity, animal weight gain and animal production per unit area indicated that management incorporating longer periods of rest compared to periods of grazing have the potential to improve animal weight gain and production per unit area, but reduce plant richness. The type of SRG system was also important, with multi-paddock SRG systems having lower plant richness relative to CG systems, and SRG systems based on seasonal or deferred grazing having greater diversity than CG systems. Most of the literature comparing SRG with CG or UG did not consider the response of ecological and animal production response variables simultaneously. Greater collaboration between ecological and animal production scientists is recommended to better understand the ecological and socio-economic trade-offs associated with different grazing management strategies. Understorey floristic species composition and plant biodiversity measures were compared between commercial properties managed under alternative grazing management (incorporating frequent and long periods of rest), traditional (continuous) grazing management, and adjacent ungrazed areas managed for conservation across a broad region of the semi-arid rangelands in western NSW. Significant variation in understorey floristic composition was driven by soil type (clay and sand), season, preceding rainfall and geographic location. These variables were the major drivers of floristic composition. The effect of grazing treatment on floristic composition at the regional scale was comparatively small and not significant. However, infrequent species were more likely to be recorded in conservation areas. Measures of floristic biodiversity varied with the scale of observation, season of sampling and soil type. In comparison to traditional grazing management, alternative grazing management generally resulted in greater understorey floristic species richness and diversity, depending on the season and scale of sampling. Few differences were found in plant species richness, diversity or functional diversity between alternatively grazed properties and adjacent areas ungrazed by commercial livestock and managed for biodiversity conservation. This suggests that alternative grazing management may be compatible with biodiversity conservation on commercial livestock properties in western NSW rangelands, but potentially at the expense of rare species. Ground cover, soil properties and landscape function were also compared between alternative grazing management, traditional grazing management and conservation management in semi-arid NSW. Alternative grazing management had greater total ground cover in comparison to traditional grazing management systems. However, both alternative and traditional grazing management treatments had significantly less ground cover than adjacent areas managed for conservation. Alternative grazing management properties did not differ significantly to areas managed for conservation in terms of landscape function, but many indices of landscape function (stability, nutrient cycling, landscape organisation index, patch area and average interpatch length) were significantly reduced under traditional grazing management compared to conservation. This suggests that alternative grazing management was more beneficial for landscape function than traditional grazing management. Significant differences were observed in floristic biodiversity measures, ground cover, soil properties and landscape function between clay and sandy soils in the study region. Clay soils had greater soil organic carbon and organic nitrogen, and lower bulk density than sandy sites. Soil stability, nutrient cycling and landscape organisation indices were also greater on clay than sand soils, and average interpatch length was shorter on clay soils. There was no difference in total ground cover between sand and clay soils, although clay soils had greater vegetative cover than sand soils, while sandy soils had greater cryptogam cover. Floristic biodiversity measures (species richness, evenness, diversity, turnover) were significantly greater on sandy than clay soils at larger plot and site scales, but there was no difference in species richness at the finest scale of sampling (1 m² quadrats). Despite the common perception that clay soils are more resilient to disturbance than sand communities, we found no difference between sand and clay soils in floristic biodiversity measures, ground cover, landscape function, soil organic carbon, soil organic nitrogen, or bulk density in response to grazing management. This indicates that alternative grazing management may provide a sustainable option for conservation of biodiversity and landscape function across both sandy and clay soils in western NSW semi-arid rangelands. Floristic composition, biodiversity measures and ground cover were also compared at a local scale between an ungrazed public nature reserve and an adjacent rotationally grazed commercial property in Acacia aneura woodland in semi-arid NSW. Significant differences in understorey floristic composition were observed between the two grazing treatments, including a greater frequency of palatable species in the nature reserve and more unpalatable species on the rotationally grazed property. There were no significant differences in understorey floristic species richness, diversity, functional diversity measures or ground cover between the nature reserve and rotationally grazed property. However, these measures increased with distance from water on the rotationally grazed property, highlighting the negative effects of increasing grazing intensity. These results suggest that at a whole-paddock scale (beyond the sacrifice zone of high grazing intensity surrounding water points), rotational grazing management, along with careful management of grazing intensity and stocking rates, has the potential to sustain biodiversity and ground cover and may offer an alternative to grazing exclusion to achieve broad-scale conservation objectives in semi-arid rangelands. However, management would still need to address the impacts on floristic composition. In conclusion, I found improved understorey plant species richness, diversity, ground cover and landscape function under alternative grazing management compared to traditional grazing management, and few differences in these measures between alternatively grazed and ungrazed areas managed for conservation. These results provide support for utilisation of alternative grazing management practices to improve biodiversity conservation and landscape function outside of the public reserve system in semi-arid rangelands. Results also show incorporation of planned periods of rest in grazing management regimes has the potential to achieve dual ecological and animal production outcomes in grazing landscapes throughout the world. Further research is necessary to understand the circumstances in which commercial grazing is compatible with the conservation of biodiversity, landscape function and animal productivity, and to identify best grazing management practices for biodiversity conservation purposes

Pollen collection by honey bee hives in almond orchards indicate diverse diets

Almond is one of the world's most economically valuable crops and many varieties require cross pollination for optimal fruit set. For this reason, western honey bee (Apis mellifera L.) hives are often placed in almond orchards. However, little is known about the usage of almond and other pollen sources by individual hives during almond bloom. Here, we investigated the timing, identity and quantity of pollen collection associated with almond floral abundance and spatial location of individual hives by sampling 440 individual pollen tray samples and counting 45,072 pollen grains from 13,200 pollen pellets collected from 80 individual hives across the flowering season in Victoria, south-eastern Australia. A large proportion of hives collected non-almond pollen in addition to almond pollen (63/80 = 79%). The weight of almond pollen collected by the hives at each sampling time was positively related to the number of concurrently open almond flowers. However, non-almond pollen richness and abundance was not related to the number of almond flowers but had a positive relationship with the weight of almond pollen collected. There was no relationship between the distance among hives and identity of pollen collected. Yet, three plant families in the study area were found to account for a high percentage of the non-almond pollen collected, Euphorbiaceae, Fabaceae and Asteraceae. Understanding crop and non-crop pollen collection could inform honey bee diet needs and identify the plant species of importance to inform best practice bee management during almond flowering