The way pollinators gather resources may play a key role for buffering their population declines. Social pollinators like bumblebees could adjust their foraging after significant workforce reductions to keep provisions to the colony optimal, especially in terms of pollen diversity and quantity. To test what effects a workforce reduction causes on the foraging for pollen, commercially-acquired colonies of the bumblebee Bombus terrestris were allowed to forage in the field and they were experimentally manipulated by removing half the number of workers. For each bumblebee, the pollen pellets were taxonomically identified with DNA metabarcoding of the ITS2 region followed by a statistical filtering based on ROC curves to filter out underrepresented OTUs. Video cameras and network analyses were employed to investigate changes in foraging strategies and behaviour. After filtering out the false-positives, HTS metabarcoding yielded a high plant diversity in the pollen pellets; for plant identity and pollen quantity traits no differences emerged between samples from treated and from control colonies, suggesting that plant choice was influenced mainly by external factors such as the plant phenology. The colonies responded to the removal of 50% of their workers by increasing the foraging activity of the remaining workers, while only negligible changes were found in diet breadth and indices describing the structure of the pollen transport network. Therefore, a consistency in the bumblebees' feeding strategies emerges in the short term despite the lowered workforce.

Czech Academy of Sciences Biology Centre Institute of Entomology České Budějovice Czech Republic

University of Milano Bicocca Department of Biotechnology and Biosciences Milan Italy

University of South Bohemia Faculty of Science Department of Zoology České Budějovice Czech Republic

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PLoS One. 2019 Dec 30;14(12):e0227453. doi: 10.1371/journal.pone.0227453. PubMed

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Individual-level specialisation and interspecific resource partitioning in bees revealed by pollen DNA metabarcoding

Updating the list of flower-visiting bees, hoverflies and wasps in the central atolls of Maldives, with notes on land-use effects