The diversity and abundance of wild insect pollinators have declined in many agricultural landscapes. Whether such declines reduce crop yields, or are mitigated by managed pollinators such as honey bees, is unclear. We found universally positive associations of fruit set with flower visitation by wild insects in 41 crop systems worldwide. In contrast, fruit set increased significantly with flower visitation by honey bees in only 14% of the systems surveyed. Overall, wild insects pollinated crops more effectively; an increase in wild insect visitation enhanced fruit set by twice as much as an equivalent increase in honey bee visitation. Visitation by wild insects and honey bees promoted fruit set independently, so pollination by managed honey bees supplemented, rather than substituted for, pollination by wild insects. Our results suggest that new practices for integrated management of both honey bees and diverse wild insect assemblages will enhance global crop yields.

There is compelling evidence that more diverse ecosystems deliver greater benefits to people, and these ecosystem services have become a key argument for biodiversity conservation. However, it is unclear how much biodiversity is needed to deliver ecosystem services in a cost-effective way. Here we show that, while the contribution of wild bees to crop production is significant, service delivery is restricted to a limited subset of all known bee species. Across crops, years and biogeographical regions, crop-visiting wild bee communities are dominated by a small number of common species, and threatened species are rarely observed on crops. Dominant crop pollinators persist under agricultural expansion and many are easily enhanced by simple conservation measures, suggesting that cost-effective management strategies to promote crop pollination should target a different set of species than management strategies to promote threatened bees. Conserving the biological diversity of bees therefore requires more than just ecosystem-service-based arguments.

Wild and managed bees are well documented as effective pollinators of global crops of economic importance. However, the contributions by pollinators other than bees have been little explored despite their potential to contribute to crop production and stability in the face of environmental change. Non-bee pollinators include flies, beetles, moths, butterflies, wasps, ants, birds, and bats, among others. Here we focus on non-bee insects and synthesize 39 field studies from five continents that directly measured the crop pollination services provided by non-bees, honey bees, and other bees to compare the relative contributions of these taxa. Non-bees performed 25-50% of the total number of flower visits. Although non-bees were less effective pollinators than bees per flower visit, they made more visits; thus these two factors compensated for each other, resulting in pollination services rendered by non-bees that were similar to those provided by bees. In the subset of studies that measured fruit set, fruit set increased with non-bee insect visits independently of bee visitation rates, indicating that non-bee insects provide a unique benefit that is not provided by bees. We also show that non-bee insects are not as reliant as bees on the presence of remnant natural or seminatural habitat in the surrounding landscape. These results strongly suggest that non-bee insect pollinators play a significant role in global crop production and respond differently than bees to landscape structure, probably making their crop pollination services more robust to changes in land use. Non-bee insects provide a valuable service and provide potential insurance against bee population declines.unmanaged pollinator | insect pollinator | fly | bee | beetle

Summary 1.The honeybee Apis mellifera is currently in decline worldwide because of the combined impacts of Colony Collapse Disorder and the Varroa destructor mite. In order to gain a balanced perspective of the importance of both wild and managed pollination services, it is essential to compare these services directly, a priori, within a cropping landscape. This process will determine the capacity of other flower visitors to act as honeybee replacements. 2. In a highly modified New Zealand agricultural landscape, we compared the pollination services provided by managed honeybees to unmanaged pollinator taxa (including flies) within a Brassica rapa var. chinensis mass flowering crop. 3. We evaluate overall pollinator effectiveness by separating the pollination service into two components: efficiency (i.e. per visit pollen deposition) and visit rate (i.e. pollinator abundance per available flower and the number of flower visits per minute). 4. We observed 31 species attending flowers of B. rapa. In addition to A. mellifera, seven insect species visited flowers frequently. These were three other bees (Lasioglossum sordidum, Bombus terrestris and Leioproctus sp.) and four flies (Dilophus nigrostigma, Melanostoma fasciatum, Melangyna novae-zelandiae and Eristalis tenax). 5. Two bee species, Bombus terrestris and Leioproctus sp. and one fly, Eristalis tenax were as efficient as the honeybee and as effective (in terms of rate of flower visitation). A higher honeybee abundance, however, resulted in it being the more effective pollinator overall. 6. Synthesis and applications. Alternative land management practices that increase the population sizes of unmanaged pollinator taxa to levels resulting in visitation frequencies as high as A. mellifera, have the potential to replace services provided by the honeybee. This will require a thorough investigation of each taxon's intrinsic biology and a change in land management practices to ensure year round refuge, feeding, nesting and other resource requirements of pollinator taxa are met.

Insects other than bees (i.e., non-bees) have been acknowledged as important crop pollinators, but our understanding of which crop plants they visit and how effective they are as crop pollinators is limited. To compare visitation and efficiency of crop-pollinating bees and non-bees at a global scale, we review the literature published from 1950 to 2018 concerning the visitors and pollinators of 105 global food crops that are known to benefit from animal pollinators. Of the 105 animal-pollinated crops, a significant proportion are visited by both bee and non-bee taxa ( n = 82; 77%), with a total gross domestic product (GDP) value of US$780.8 billion. For crops with a narrower range of visitors, those that favor non-bees ( n = 8) have a value of US$1.2 billion, compared to those that favor bees ( n = 15), with a value of US$19.0 billion. Limited pollinator efficiency data were available for one or more taxa in only half of the crops ( n = 61; 58%). Among the non-bees, some families were recorded visiting a wide range of crops (>12), including six families of flies (Syrphidae, Calliphoridae, Muscidae, Sarcophagidae, Tachinidae, and Bombyliidae), two beetle families (Coccinelidae and Nitidulidae), ants (Formicidae), wasps (Vespidae), and four families of moths and butterflies (Hesperiidae, Lycaenidae, Nymphalidae, and Pieridae). Among the non-bees, taxa within the dipteran families Syrphidae and Calliphoridae were the most common visitors to the most crops, but this may be an artifact of the limited data available. The diversity of species and life histories in these groups of lesser-known pollinators indicates that diet, larval requirements, and other reproductive needs will require alternative habitat management practices to bees.

Pollinator decline has attracted global attention and substantial efforts are underway to respond through national pollinator strategies and action plans. These policy responses require clarity on what is driving pollinator decline and what risks it generates for society in different parts of the world. Using a formal expert elicitation process, we evaluated the relative regional and global importance of eight drivers of pollinator decline and ten consequent risks to human well-being. Our results indicate that global policy responses should focus on reducing pressure from changes in land cover and configuration, land management and pesticides, as these were considered very important drivers in most regions. We quantify how the importance of drivers and risks from pollinator decline, differ among regions. For example, losing access to managed pollinators was considered a serious risk only for people in North America, whereas yield instability in pollinator-dependent crops was classed as a serious or high risk in four regions but only a moderate risk in Europe and North America. Overall, perceived risks were substantially higher in the Global South. Despite extensive research on pollinator decline, our analysis reveals considerable scientific uncertainty about what this means for human society.

Summary1 A data base on the flowering phenology of the Wet Tropics bioregion of far northern Queensland, Australia, has been constructed, based upon over 36 774 records from two Queensland-based herbaria. 2 Flowering patterns have been analysed against the predictions of three overlapping hypotheses based on climatic, biotic and phylogenetic explanations. No one hypothesis is supported to the exclusion of the others. 3 Patterns of flowering in the Wet Tropics show marked seasonal increases and decreases, except in the northern lowlands. In general this seasonality correlates with rainfall and temperature and is exacerbated by increasing latitude and altitude. 4 There is little or no statistical evidence for the over-dispersion of flowering times that would indicate a competition-avoidance mechanism: flowering within taxa or morphological groups tends to be clumped (and if not, is random). 5 That clumping of flowering within taxa does not coincide with a single season provides support for a mass action hypothesis based on the minimization of generalist predation and/or the avoidance of flower predation. 6 Timing of flowering did show some consistency among species within genera and within families, but there was little consistency at higher taxonomic levels. Clear separation of the biotic and phylogenetic hypotheses requires greater knowledge of pollination ecology and phylogeny of this large and diverse flora. 7 Understanding of flowering patterns and their underlying determining mechanisms is a key to assessing the ecosystem health of the forest. Our results highlight the importance of competitive interactions and of physical and evolutionary factors as determinants of flowering time, intensity and co-occurrence in tropical forests.

Summary1. Recent declines in honeybee populations have focused attention on the potential for unmanaged insects to replace them as pollinators of food crops. The capacity of unmanaged pollinators to replace services currently provided by honeybees depends on the spatial and temporal variability of these services, but few quantitative assessments currently exist. 2. We investigated spatial variation in pollinator importance by comparing pollinator efficiency and effectiveness in stigmatic pollen loads, stigmatic contact and visitation rate between honeybees and the seven most abundant unmanaged taxa in 2007. We assessed temporal variability in pollinator visitation using floral visits recorded three times a day over four consecutive years (2005)(2006)(2007)(2008) in 43 'Pak Choi' Brassica rapa ssp. chinensis mass flowering fields in the Canterbury region of New Zealand. Further, we compared the aggregate effect of the unmanaged pollinator assemblage to the managed honeybee. 3. Pak Choi was visited by many insect species that vary in abundance and effectiveness as pollen transfer agents. There was spatial variation in the four measures of pollinator importance. Pollen deposited on stigmas and flower visits per minute were not significantly different comparing the unmanaged assemblage to honeybees, although stigmatic contact and visitor abundance per number of open flowers were greater in honeybees. 4. Unmanaged taxa were frequent visitors to the crop in all 4 years. The pooled services provided by the unmanaged assemblage did not differ within a day and were equal to or greater than those provided by honeybees in 2 of the 4 years. Pollinator importance changed little irrespective of the spatial and temporal variations among taxa. 5. Synthesis and applications. The results of this study suggest that some unmanaged insect taxa are capable of providing consistent pollination services over a 4-year period in a commercial mass flowering crop. As these taxa already contribute substantially to the pollination of food crops, they offer a safety net in the case of sudden collapse of managed honeybee hives. To optimize pollination services, we recommend pollinator-specific farm management practices that consider the needs of both managed and unmanaged pollinator taxa.