On managing the Red mason Bee (Osmia bicornis) in apple orchards.

International audienceA worldwide decline of pollinator abundance is recorded and the worldwide pollination of insect-pollinated crops has traditionally depended on a single species, the honeybee. The risks of relying on a single species are obvious. Other species have been developed for particular crops. Here we present an extension of the framework of Bosch and Kemp (2002) that deals on how to develop a bee species into a crop pollinator. We used nesting aids in different settings to address five important issues that are necessary for an effective management of a bee species in a commercial setting. Our study system was the red mason bee (Osmia bicornis) in apple orchards in eastern Germany, but our approach should be transferable to other settings. The first issue was to demonstrate that it is possible to increase population size of O. bicornis by providing nesting aids. Second, we present how someone can study landscape features that promote the occurrence and abundance of O. bicornis. Further, we studied the dispersal of the species inside the orchard, and could demonstrate that bees prefer to disperse along lines of trees. Finally, we studied the effect of nesting substrate and type of farming on the recruitment of bees. We found a close relationship between the length of nesting tubes and achieved sex ratio and a negative effect of conventional farming on the number of nests built. We conclude with recommendations on how our findings can be used to optimize the management of O. bicornis in apple orchards

Fragmentation of nest and foraging habitat affects time budgets of solitary bees, their fitness and pollination services, depending on traits: Results from an individual-based model

<div><p>Solitary bees are important but declining wild pollinators. During daily foraging in agricultural landscapes, they encounter a mosaic of patches with nest and foraging habitat and unsuitable matrix. It is insufficiently clear how spatial allocation of nesting and foraging resources and foraging traits of bees affect their daily foraging performance. We investigated potential brood cell construction (as proxy of fitness), number of visited flowers, foraging habitat visitation and foraging distance (pollination proxies) with the model SOLBEE (simulating pollen transport by solitary bees, tested and validated in an earlier study), for landscapes varying in landscape fragmentation and spatial allocation of nesting and foraging resources. Simulated bees varied in body size and nesting preference. We aimed to understand effects of landscape fragmentation and bee traits on bee fitness and the pollination services bees provide, as well as interactions between them, and the general consequences it has to our understanding of the system. This broad scope gives multiple key results. 1) Body size determines fitness more than landscape fragmentation, with large bees building fewer brood cells. High pollen requirements for large bees and the related high time budgets for visiting many flowers may not compensate for faster flight speeds and short handling times on flowers, giving them overall a disadvantage compared to small bees. 2) Nest preference does affect distribution of bees over the landscape, with cavity-nesting bees being restricted to nesting along field edges, which inevitably leads to performance reductions. Fragmentation mitigates this for cavity-nesting bees through increased edge habitat. 3) Landscape fragmentation alone had a relatively small effect on all responses. Instead, the local ratio of nest to foraging habitat affected bee fitness positively through reduced local competition. The spatial coverage of pollination increases steeply in response to this ratio for all bee sizes. The nest to foraging habitat ratio, a strong habitat proxy incorporating fragmentation could be a promising and practical measure for comparing landscape suitability for pollinators. 4) The number of flower visits was hardly affected by resource allocation, but predominantly by bee size. 5) In landscapes with the highest visitation coverage, bees flew least far, suggesting that these pollination proxies are subject to a trade-off between either longer pollen transport distances or a better pollination coverage, linked to how nests are distributed over the landscape rather than being affected by bee size.</p></div

Simulated responses to landscape fragmentation in landscapes with different foraging habitat availability.

<p>Each model response, i.e. brood cells (a), flower visits (b), visited foraging habitat (c) and foraging distance (d), is displayed for six bee types (panels A-F) to illustrate the effect of traits. The panels depict from the left to the right small (panel A, D), intermediate (panel B, E) and large bees (panel C, F) and from top to bottom wood-nesting (panel A-C) and soil-nesting (panel D-F) bees. Within each panel 100 different simulated landscapes are displayed and characterized by a gradient of <i>landscape fragmentation</i> (bottom to top) and <i>foraging habitat availability</i> (left to right), with each landscape being represented by a single coloured square (legend on the right for each response, accompanied by natural ranges) being the mean of 20 replicate simulations. Contour lines visually guide the gradients that are present in these 100 means (calculated by prediction). The standard error to each mean of 20 replicates, as complementary information, is indicated by a circle. The smallest circle always represents zero, while the largest circle represents 0.09 for brood cells, 0.05 for flower visits, 2.29 for visited foraging habitat and 4.92 for foraging distance. Natural ranges (black lines and extreme values as grey dotted line) were reviewed and discussed (such values are rarely measured and not well known for bees of different size) in an earlier manuscript ([<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0188269#pone.0188269.ref037" target="_blank">37</a>]) and are added here for rough comparison with the results only (as the model's aim is to understand the system and not to reproduce exact values). Photographic material by the main author, also available on Wikimedia.</p

Comparison of two vegetation types for their effect on visited foraging habitat and for two conflicting pollination proxies both fitted with logistic functions.

<p>Visited foraging habitat in response to the ratio of nest to foraging habitat is plotted for a) initial vegetation (same conditions as in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0188269#pone.0188269.g003" target="_blank">Fig 3i</a>) and for b) with adjusted vegetation parameters. The logistic curves are fitted for all bees independent of nesting preference and body length (inlay with fitted values) and untransformed to the main plot. Two conflicting response variables, visited foraging habitat and foraging distance, are plotted against each other for: c) initial vegetation and for d) with adjusted vegetation parameters. The logistic curves are fitted for each body size separately (inlay with fitted values for intermediate sized bees) and untransformed to the main plot. Details for all curves are given in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0188269#pone.0188269.t005" target="_blank">Table 5</a>. All remaining conditions are the same as described for <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0188269#pone.0188269.g003" target="_blank">Fig 3</a>.</p

Analysis of variance for the number of brood cells, flower visits, visited foraging habitat and foraging distance in response to landscape fragmentation.

<p>Analysis of variance for the number of brood cells, flower visits, visited foraging habitat and foraging distance in response to landscape fragmentation.</p

Analysis of variance for the number of brood cells, flower visits, visited foraging habitat and foraging distance (top to bottom) in response to one of three focal predictors; nest habitat availability, local bee density and ratio of nest to foraging habitat (left to right) based on 20 replicates.

<p>Analysis of variance for the number of brood cells, flower visits, visited foraging habitat and foraging distance (top to bottom) in response to one of three focal predictors; nest habitat availability, local bee density and ratio of nest to foraging habitat (left to right) based on 20 replicates.</p

The simulation results in response to single landscape-level gradients.

<p>The simulation results for the four responses (rows)brood cells (a-c), flower visits (d-f), visited foraging habitat (g-i) and foraging distance (j-l) in response to three landscape-level gradients (columns) of: nest habitat availability (left column, a,d,g,j), local bee density (middle column, b,e,h,k) and the ratio of nest to foraging habitat (right column, c,f,i,l). The three y-axes in each row have equal dimensions and are labelled on the most left figure of each row, while the four x-axes in each column have equal dimensions as well and are labelled on the bottom figure of each column. Points are plotted for three replicate simulations (for 100 landscapes) with six colours representing the different bee types (i.e. 1800 points per plot). Lines are based on the full linear models with 20 replicate simulations. How landscape fragmentation affects each gradient is visualized with a landscape with intermediate <i>foraging habitat availability</i> (0.45) increasing from low <i>landscape fragmentation</i> (0.05) to intermediate (0.45) to high (0.95) for small, intermediate sized and large wood-nesting bees (i.e. nine points of 1800 are plotted with extra symbol).</p

List of model parameters with definitions, units and simulated values.

<p>List of model parameters with definitions, units and simulated values.</p