Microbiota and pathogens in an invasive bee: Megachile sculpturalis from native and invaded regions.

The present study aimed to characterise the bacterial, fungal and parasite gut community of the invasive bee Megachile sculpturalis sampled from native (Japan) and invaded (USA and France) regions via 16S rRNA and ITS2 amplicon sequencing and PCR detection of bee microparasites. The bacterial and fungal gut microbiota communities in bees from invaded regions were highly similar and differed strongly from those obtained in Japan. Core amplicon sequence variants (ASVs) within each population represented environmental micro-organisms commonly present in bee-associated niches that likely provide beneficial functions to their host. Although the overall bacterial and fungal communities of the invasive M. sculpturalis in France and the co-foraging native bees Anthidium florentinum and Halictus scabiosae, were significantly different, five out of eight core ASVs were shared suggesting common environmental sources and potential transmission. None of the 46 M. sculpturalis bees analysed harboured known bee pathogens, while microparasite infections were common in A. florentinum, and rare in H. scabiosae. A common shift in the gut microbiota of M. sculpturalis in invaded regions as a response to changed environmental conditions, or a founder effect coupled to population re-establishment in the invaded regions may explain the observed microbial community profiles and the absence of parasites. While the role of pathogen pressure in shaping biological invasions is still debated, the absence of natural enemies may contribute to the invasion success of M. sculpturalis.

The impact of mass-flowering crops on bee pathogen dynamics.

Nearly two fifths of the Earth's land area is currently used for agriculture, substantially impacting the environment and ecosystems. Besides the direct impact through land use change, intensive agriculture can also have an indirect impact, for example by changing wildlife epidemiology. We review here the potential effects of mass-flowering crops (MFCs), which are rapidly expanding in global cropping area, on the epidemiology of known pathogens in bee pollinators. We bring together the fifty MFCs with largest global area harvested and give an overview of their pollination dependency as well as their impact on bee pollinators. When in bloom these crops provide an abundance of flowers, which can provide nutrition for bees and increase bee reproduction. After their short bloom peak, however, the fields turn into green deserts. These big changes in floral availability strongly affect the plant-pollinator network, which in turn affects the pathogen transmission network, mediated by shared flowers. We address this dual role of flowers provided by MFCs, serving as nutritional resources as well as pathogen transmission spots, and bring together the current knowledge to assess how MFCs could affect pathogen prevalence in bee pollinator communities.

On the road: Anthropogenic factors drive the invasion risk of a wild solitary bee species.

Complex biotic networks of invaders and their new environments pose immense challenges for researchers aiming to predict current and future occupancy of introduced species. This might be especially true for invasive bees, as they enter novel trophic interactions. Little attention has been paid to solitary, invasive wild bees, despite their increasing recognition as a potential global threat to biodiversity. Here, we present the first comprehensive species distribution modelling approach targeting the invasive bee Megachile sculpturalis, which is currently undergoing parallel range expansion in North America and Europe. While the species has largely colonised the most highly suitable areas of North America over the past decades, its invasion of Europe seems to be in its early stages. We showed that its current distribution is largely explained by anthropogenic factors, suggesting that its spread is facilitated by road and maritime traffic, largely beyond its intrinsic dispersal ability. Our results suggest that M. sculpturalis is likely to be negatively affected by future climate change in North America, while in Europe the potential suitable areas at-risk of invasion remain equally large. Based on our study, we emphasise the role of expert knowledge for evaluation of ecologically meaningful variables implemented and interpreted for species distribution modelling. We strongly recommend that the monitoring of this and other invasive pollinator species should be prioritised in areas identified as at-risk, alongside development of effective management strategies.