Pollen metabarcoding is emerging as
a powerful tool for ecological research and offers
unprecedented scale in citizen science projects for
environmental monitoring via honey bees. Biases
in metabarcoding can be introduced at any stage of
sample processing and preservation is at the forefront
of the pipeline. While in metabarcoding studies
pollen has been preserved at − 20 °C (FRZ), this
is not the best method for citizen scientists. Herein,
we compared this method with ethanol (EtOH), silica
gel (SG) and room temperature (RT) for preservation
of pollen collected from hives in Austria and
Denmark. After ~ 4 months of storage, DNAs were extracted with a food kit, and their quality and concentration
measured. Most DNA extracts exhibited
260/280 absorbance ratios close to the optimal 1.8,
with RT samples from Austria performing slightly
worse than FRZ and SG samples (P < 0.027). Statistical
differences were also detected for DNA concentration,
with EtOH samples producing lower yields
than RT and FRZ samples in both countries and SG
in Austria (P < 0.042). Yet, qualitative and quantitative
assessments of floral composition obtained using
high-throughput sequencing with the ITS2 barcode
gave non-significant effects of preservation methods
on richness, relative abundance and Shannon diversity,
in both countries. While freezing and ethanol are
commonly employed for archiving tissue for molecular
applications, desiccation is cheaper and easier to use regarding both storage and transportation. Since
SG is less dependent on ambient humidity and less
prone to contamination than RT, we recommend
SG for preserving pollen for metabarcoding. SG is
straightforward for laymen to use and hence robust
for widespread application in citizen science studies.
We are deeply indebted to Susana Lopes
and Maria Magalhães, from CIBIO—Research Centre in Biodiversity
and Genetic Resources—InBIO Associate Laboratory,
for their time devoted to library preparation and sequencing
in the MiSeq. AQ acknowledges the PhD scholarship
(DFA/BD/5155/2020) funded by FCT. This work was funded by the Health and Food
Safety Directorate General, European Commission through the
project INSIGNIA—Environmental monitoring of pesticide
use through honeybees SANTE/E4/SI2.788418-SI2.788452-
INSIGINIA-PP-1–1-2018. Fundação para a Ciência e a Tecnologia
(FCT) provided financial support by national funds (FCT/MCTES) to CIMO (UIDB/00690/2020).
