*2.1. Bee Pollen Samples*

In this study, 31 bee pollen samples from Galicia (Northwest Spain) were analyzed. The samples were collected using pollen traps from *Apis mellifera* hives in 19 different apiaries. The geographical origin of the pollen samples collected is shown in Figure 1. The apiaries were distributed in the four provinces of the Galician autonomous community (A Coruña, Lugo, Pontevedra and Ourense). Specifically, in A Coruña the samples were collected from 4 apiaries (9 samples), in Lugo from 3 apiaries (4 samples), in Pontevedra from 3 apiaries (4 samples) and in Ourense from 9 apiaries (14 samples). After collection,

the bee pollen samples were cleaned of impurities (such as parts of dead bees or remains of wax), and until further analysis were stored at −20 ◦C.

**Figure 1.** Distribution of geographical origin by municipality in blue of the bee pollen samples in Galicia (Northwest Spain). Created with Datawrapper.
