Bee-plant interactions of Megachile sculpturalis: evidence vs. misconceptions, basic patterns, and the way forward

Abstract

There is a growing concern about the current trends in alien bee introductions, regarding their potential to cause various environmental problems. Among other negative effects, non-native bees may alter the pollination interactions and reproduction of various plants, including the enhancement of invasive ones. More generally, it is important to understand trophic interactions of each introduced bee in a non-native range, in order to evaluate its potential to become a successful invader, and to establish an efficient monitoring. We studied the trophic affinities of Megachile sculpturalis, an alien bee native to East Asia which is now widespread in North America and Europe (since 1994 and 2008, respectively). This bee is commonly referred to as polylectic, but without clear evaluation of the documented patterns of visitation and pollen usage, or possible source of evidence bias. The genuine trophic preferences of this species are still insufficiently clear, to some extent even controversial or partly misinterpreted. We compiled extensive evidence of M. sculpturalis plant visitations from various public sources and our unpublished data: on the worldwide basis until 2019, and at European scale for 2020–2021 (after initiating the targeted monitoring and citizen science engagement). We designed a semi quantitative approach to evaluate various obscured or contentious patterns in food-plant preferences (relevance of plant phylogenetic relatedness vs. geographic origin, relevance of availability in spatial and phenological aspect, recording biases, etc.). With limited availability of direct analyses of pollen usage by bees, we indirectly quantified the relative merits of compiled interactions (counts of localities, specimen totals, female presences, pollen collecting). Worldwide, Megachile sculpturalis was recorded on over 75 plant genera and at least 25 families. Majority of recorded visitations were made on species of E-Asian Fabaceae, with greatest share of the single genus Styphnolobium. Generally, the Fabaceae account for the highest share of female-based records, and largely dominate in pollen-based records. Arguably, a more suitable category for M. sculpturalis trophic patterns could be the mesolecty, or at most a polylecty with very strict and narrow preference. Our parallel extensive metabarcoding survey of bee-collected pollen (on-going) indicates a possibly more complex usage pattern.