2.2 Pollinator insects and plant characterization
Sampling activities were performed in October 2019, from 9:00 to 16:00 only with good climate conditions. Pollinator insects were sampled by hand-collecting flower visitors through entomological nets along free transects around and crossing over an area of continuous vegetation about 50 m x 50 m at each sampling location. Pollinator insects were captured after being observed foraging on flowers for a few seconds and captures were performed during a fixed time of three hours to allow unbiased comparison between sampling sites (similarly to Tommasi et al., 2021 a). After collection, each insect was individually stored in a clean tube and filled with 70% ethanol. A clean entomological net was used in each sampling site to prevent cross contamination between samples from different sites.
Insects identification was performed through morphological inspection and via standard DNA barcoding (Supporting information - Table S2). Specifically, insects were first sorted at the lowest possible taxonomic level (family or genus) following morphological criteria and identification keys (e.g. , Bratra, 1977; Gupta, 2003; Thompson, 1981). Morpho-species grouping was subsequently confirmed by analysing representative individuals (1- 11 individuals representative for sex and atoll of provenance) for each morpho-species through a standard DNA barcoding approach using primers LCO1490 and HCO2198 (Folmer et al., 1994) and the laboratory protocols described in Galimberti et al., 2021. For doubtful identifications where two or more candidate DNA barcode identification were equally likely, a detailed morphological scrutiny was additionally performed by an expert (author PB). Flower species richness was also estimated identifying all the flowering species observed in the whole area involved in insect sampling and plants were identified in the field or in the lab following Sujanapal & Sankaran (2016). Sampling localities and details are available in BOLD under the project code ZPLML (https://www.boldsystems.org/index.php/MAS_Management_DataConsole?codes=ZPLML) and are also reported in Supporting information - Table S1.