DNA barcoding to identify leaf preference of leafcutting bees

Abstract

Leafcutting bees (Megachile: Megachilidae) cut leaves from various trees, shrubs, wildflowers and grasses to partition and encase brood cells in hollow plant stems, decaying logs or in the ground. The identification of preferred plant species via morphological characters of the leaf fragments is challenging and direct observation of bees cutting leaves from certain plant species are difficult. As such, data are poor on leaf preference of leafcutting bees. In this study, I use DNA barcoding of the rcbL and ITS2 regions to identify and compare leaf preference of three Megachile bee species widespread in Toronto, Canada. Nests were opened and one leaf piece from one cell per nest of the native M. pugnata Say (N=45 leaf pieces), and the introduced M. rotundata Fabricius (N=64) and M. centuncularis (L.) (N=65) were analysed. From 174 individual DNA sequences, 54 plant species were identified. Preference by M. rotundata was most diverse (36 leaf species, H′=3.08, phylogenetic diversity (pd)=2.97), followed by M. centuncularis (23 species, H′=2.38, pd=1.51) then M. pugnata (18 species, H′=1.87, pd=1.22). Cluster analysis revealed significant overlap in leaf choice of M. rotundata and M. centuncularis. There was no significant preference for native leaves, and only M. centuncularis showed preference for leaves of woody plants over perennials. Interestingly, antimicrobial properties were present in all but six plants collected; all these were exotic plants and none were collected by the native bee, M. pugnata. These missing details in interpreting what bees need offers valuable information for conservation by accounting for necessary (and potentially limiting) nesting materials.

Foraging preferences of leafcutter bees in three contrasting geographical zones

“…The bees cut and collect circular to elliptical leaf pieces (Figure ) and line the brood cells with a roll of layered discs. A single brood cell may contain 50–100 leaf discs; depending on the size of the cavity, an aboveground nest may contain 1–11 brood cells (MacIvor, ; Sabino & Antonini, ), while the subterranean nests contain a single brood cell (Williams et al., ). The leaf discs are also used to partition the brood cells.…”

“…Surprisingly, information on which species of plants leafcutter bees choose and why is almost entirely lacking (but see, MacIvor, ; Kambli et al., ). We do not know whether the leafcutter bees have preference for leaves of certain plant clades, or leaves with certain physical characteristics.…”

Evolution of leaf-cutter behavior in bees (Hymenoptera: Megachilidae) as inferred from total-evidence tip-dating analyses

“…The study of MacIvor (2016) supports the second adaptive hypothesis. For example, Megachile (Sayapis) pugnata Say, a species with odontogenic laminae only, significantly uses less plant species than M. (Megachile) centuncularis and M. rotundata, species from lineages that developed both types of laminae (MacIvor, 2016). However, leaf choice might not only depend on the ability to cut certain types of leaves, but also on the local availability as well as on their chemichal, mechanical, and antimicrobial properties.…”

Notes on a nest of Megachile (Moureapis) apicipennis Schrottky (Megachilidae) constructed in an abandoned gallery of Xylocopa Frontalis (Olivier) (Apidae)

“…in cells built by females of M. maculata Smith. Other leafcutting bee species belonging to different subgenera, in contrast, collect leaves from a high diversity of plant species ranging from eight to 20 plant families (MacIvor, 2016). The author reported that females of Megachile (Eutricharaea) rotundata (Fabricius) preferred leaves from Fabaceae to the other nine families whereas Rosaceae species were more used by both Megachile (Megachile) centuncularis (L.) and Megachile (Sayapis) pugnata Say.…”

“…The author reported that females of Megachile (Eutricharaea) rotundata (Fabricius) preferred leaves from Fabaceae to the other nine families whereas Rosaceae species were more used by both Megachile (Megachile) centuncularis (L.) and Megachile (Sayapis) pugnata Say. In spite of the high richness of plant species used by those three Megachile spp., MacIvor (2016) pointed out that almost all plant species identified from nest samples had antimicrobial properties, a feature that might inform selection among leaf types.…”