Decline of six native mason bee species following the arrival of an exotic congener

Abstract

A potential driver of pollinator declines that has been hypothesized but seldom documented is the introduction of exotic pollinator species. International trade often involves movement of many insect pollinators, especially bees, beyond their natural range. For agricultural purposes or by inadvertent cargo shipment, bee species successfully establishing in new ranges could compete with native bees for food and nesting resources. In the Mid-Atlantic United States, two Asian species of mason bee (Osmia taurus and O. cornifrons) have become recently established. Using pan-trap records from the Mid-Atlantic US, we examined catch abundance of two exotic and six native Osmia species over the span of fifteen years (2003–2017) to estimate abundance changes. All native species showed substantial annual declines, resulting in cumulative catch losses ranging 76–91% since 2003. Exotic species fared much better, with O. cornifrons stable and O. taurus increasing by 800% since 2003. We characterize the areas of niche overlap that may lead to competition between native and exotic species of Osmia, and we discuss how disease spillover and enemy release in this system may result in the patterns we document.

A keystone mutualism promotes resistance to invasion

“…It is known that invasive pollinators have a strong negative effect on congener native species (Inoue et al, 2008;Morales et al, 2013). For example, LeCroy et al (2020) have recently demonstrated how the presence of a non-native mason bee Osmia taurus leads to declines in the abundance of six native congener species (Osmia sps.). Our study shows that an invasive pollinator not only can drastically affect congener species interactions (B. dalhbomii and B. ruderatus), but also reduces direct and indirect ecological interactions of native non-congener species (P. albopilosa, M. gayi and R. mutabilis).…”

Ultraconserved element phylogenomics and biogeography of the agriculturally important mason bee subgenus Osmia (Osmia)

“…These species have become established in the eastern U.S. and because they share similar host‐plant ranges and nesting requirements with the native Osmia lignaria lignaria and other Osmia species, there has been concern that these introduced species might be competing with and mediating population declines in native species. Recent research suggests that this may be the case (LeCroy et al ., 2020; but see also Centrella, 2019). Other species have also been introduced but have not yet established outside of their native ranges.…”

Intensive monitoring for bees in North America: indispensable or improvident?

“…LeCroy et al . (2020) needed 15 years data to report on precipitous declines of several species of Osmia bees associated with two invasive congeners; actions to reverse these declines were not proposed, nor are any realistic ones immediately evident. Powney et al .…”

“…Other recent field studies of bees attest to the length of time required to establish significant trends. LeCroy et al (2020) needed 15 years data to report on precipitous declines of several species of Osmia bees associated with two invasive congeners; actions to reverse these declines were not proposed, nor are any realistic ones immediately evident. Powney et al (2019) used Bayesian analysis of 33 years of haphazardly gathered survey data in the United Kingdom to report declines in patch occupancy rates for 32% of solitary bee species; no testable hypotheses were offered to explain these declines nor were actions proposed to reverse them.…”