Pollen Metabarcoding and Pollinator Networks
The pollen loads of 267 insects were successfully analyzed for plant
family or genus composition. The total read count after filtering was
15,205,661 ranging from 22 (Sylvanelater cylindriformis ) to 2.7 M
(Toxomerus marginatus ) (Supplementary Table 3). After removal of
OTUs (operational taxonomic units) from negative controls, we found 129
plant genera with at least 98% hit match to reference library
(Supplementary Table 4). As a more conservative estimate, 49 plant
families were found across all insects (Supplementary Table 3, Figure
2). The relative abundance of sequence reads was used as a proxy of
relative abundance of pollen load composition for the remaining analysis
(Richardson et al. 2015, Kraaijeveld et al. 2015, Pornon et al. 2017).
All species, apart from one undetermined cecidomyiid had strawberry
pollen on their bodies. Species with only strawberry pollen on their
bodies were the dipterans Lucilia sericata, Liohippelates
bishoppi, Discomyza incurva , the coleopterans Collops
quadrimaculatus, Macrodactylus subspinosus, Sylvanelater
cylindriformis , and the hemipteran Lygaeus kalmii (Supplementary
Table 3). The most generalist families were Syrphidae (for which pollen
data from 32 plant families, and 73 genera were recorded), Pollenidae
(29 plant families, 55 genera), and Anthomyiidae (22 plant families, 43
genera). At first glance syrphids appeared quite generalist in their
choice of flower visitations. However, this picture was driven by two
generalist species (Toxomerus marginatus and Sphaerophoria
scripta ) and the remaining species were more selective, carrying pollen
from only 2-6 plant species (Figure 3).