A framework for comparing pollinator performance: effectiveness and efficiency

Measuring pollinator performance has become increasingly important with emerging needs for risk assessment in conservation and sustainable agriculture that require multi-year and multi-site comparisons across studies. However, comparing pollinator performance across studies is difficult because of the diversity of concepts and disparate methods in use. Our review of the literature shows many unresolved ambiguities. Two different assessment concepts predominate: the first estimates stigmatic pollen deposition and the underlying pollinator behaviour parameters, while the second estimates the pollinator’s contribution to plant reproductive success, for example in terms of seed set. Both concepts include a number of parameters combined in diverse ways and named under a diversity of synonyms and homonyms. However, these concepts are overlapping because pollen deposition success is the most frequently used proxy for assessing the pollinator’s contribution to plant reproductive success. We analyse the diverse concepts and methods in the context of a new proposed conceptual framework with a modular approach based on pollen deposition, visit frequency, and contribution to seed set relative to the plant’s maximum female reproductive potential. A system of equations is proposed to optimize the balance between idealised theoretical concepts and practical operational methods. Our framework permits comparisons over a range of floral phenotypes, and spatial and temporal scales, because scaling up is based on the same fundamental unit of analysis, the single visit

Monitoring Solitary Bees in Modified Wildland Habitats: Implications for Bee Ecology and Conservation

The long-term goal of this study was to use solitary bees to assess the impact of advancing Africanized honey bees (Apis mellifcra scutellata Lepeletier) on the native California bee fauna. Cavity-nesting, solitary bee species were systematically monitored in wooden trap nests at 6 sites in northern central California from 1990 to 1992. Three sites were in the San Joaquin Valley in wildlife refuges or preserves; 3 were in coastal mountain or Sierran foothill parks or reserves. Differences in frequencies of nesting bees were observed and recorded among sites and habitats through time. A Poisson regression indicated that all explanatory variables and their 1st order interactions were highly significant. There were significant differences among bee taxa, sites and years, and their interactions (bee X site; bee X year; site X year). Megachile species were the predominant cavity nesters in the 3 valley sites; Osmia species were the common group in coastal mountain I foothill sites. In a computer simulation, using a variation of the Poisson regression, several significant differences were also observed between yearly frequency counts for certain bee species at the same site. Possible reasons for year to year changes included differential natural mortality, extreme annual weather patterns, use of marginal habitats, and negative impacts from exotic solitary bee species. Three exotic megachilids (Megachile rotundata (F.), M. apicalis Spinola, and M. concinna Smith) have successfully invaded and become established in California. Possibly, M. apicalis has affected other cavity nesting bee species, including the exotic M. rotundata in our Central Valley sites

Winter 2016 honey bee colony losses in New Zealand

<p>Estimating winter losses for managed honey bee (<i>Apis mellifera</i>) colonies is critical for understanding hive productivity and health. This study reports estimates of overwinter colony losses in New Zealand, which has seen exponential growth in the number of managed colonies in recent years. Over 35% of all beekeepers, and 50% of all commercial beekeepers in the country responded to the internet-based 2016 New Zealand Colony Loss Survey, providing detailed information on over 275,000 colonies (over 40% of all registered colonies) that entered winter 2016. Using three different methods, we estimate overall winter losses to be below 10%. However, nearly 29% of beekeepers lost more than 15% of their colonies over winter 2016, and nearly 25% of beekeepers lost more than 20%, indicating considerable skewness. These results are subject to strong regional variation, with the highest losses reported in areas with significant mānuka resources. Similarly, non-commercial beekeepers report substantially higher loss rates than commercial beekeepers. Beekeepers who lost colonies over the winter of 2016 most frequently attributed the cause to colony death, queen problems, or wasps. However, varroa and competition for apiary sites were also identified as important areas of concern. In this analysis, we explore variation in both region and operation size for all five of these challenges.</p

Alternative pollinator taxa are equally efficient but not as effective as the honeybee in a mass flowering crop

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