Abstract
Simple SummaryAlien bee species could have detrimental effects; in particular, they may compete with native bee species for floral resources or nesting sites. Here, we first studied the interaction in artificial trap nests, installed in a semi-urban area of north-western Italy, between the first exotic bee in Europe, Megachile sculpturalis, and native wild bees. Second, we evaluated the performance of the exotic bee by means of the sex ratio, and we screened for the presence of natural enemies affecting its brood. Our results showed that M. sculpturalis brood cells cohabited tunnels with the native Osmia cornuta. Given the exotic cells’ position within tunnels and their resin-based material, exotic cells may act as a block for native bee emergence. Moreover, our study revealed a strong male-biased sex ratio, suggesting a suboptimal reproductive trend for the M. sculpturalis local population. Additionally, we documented for the first time the presence of three natural enemies on the brood of the exotic bee that are common on native co-nesting bees. These novel findings broaden the knowledge on solitary bee invasions.Megachile sculpturalis (Smith, 1853) is the first exotic bee species in Europe. Its remarkably fast expansion across this continent is leading to a growing concern on the extent of negative impacts to the native fauna. To evaluate the interactions of exotic bees with local wild bees, we set up trap nests for above-ground nesting bees on a semi-urban area of north-western Italy. We aimed to investigate the interaction in artificial traps between the exotic and native wild bees and to assess offspring traits accounting for exotic bee fitness: progeny sex ratio and incidence of natural enemies. We found that the tunnels occupied by exotic bees were already cohabited by O. cornuta, and thus the cells of later nesting alien bees may block the native bee emergence for the next year. The progeny sex ratio of M. sculpturalis was strongly unbalanced toward males, indicating a temporary adverse population trend in the local invaded area. In addition, we documented the presence of three native natural enemies affecting the brood of the exotic bee. Our results bring out new insights on how the M. sculpturalis indirectly competes with native species and on its performance in new locations.
Highlights
This study provides new insights on traits linked to M. sculpturalis fitness in the new colonized area in Italy where it has been present since 2009 [5], and it adds novel evidence of likely negative effects of this exotic bee on native bee species
229 out of a total of 324 available tunnels were occupied by two species, M. sculpturalis and O. cornuta, and none of the trap nests were colonized by further wild bee species
25% of nests were built by M. sculpturalis, while 75% were built by O. cornuta (Table 1)
Summary
Introduced non-native bees (Hymenoptera apoidea) can enhance pollination service, but they can have detrimental effects on local ecosystems [1]. Competition for floral resources or nesting sites, diseases transmission and changes in the pollination network are the mechanisms that have been deemed responsible for impacts directly on native bees [2]. Megachile sculpturalis Smith, 1853, native from eastern Asia (China, Korea, Japan), is the first unintentionally introduced bee species in Europe, and it showed a remarkably fast spread across this continent. Since 2008, it expanded from southern France [4] towards eastern Europe [5,6,7,8,9,10], reaching the Crimea peninsula in 2018 [11] and westwards eastern
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