Historical decrease in agricultural landscape diversity is associated with shifts in bumble bee species occurrence

Abstract

Agricultural intensification is a key suspect among putative drivers of recent insect declines, but an explicit link between historical change in agricultural land cover and insect occurrence is lacking. Determining whether agriculture impacts beneficial insects (e.g. pollinators), is crucial to enhancing agricultural sustainability. Here, we combine large spatiotemporal sets of historical bumble bee and agricultural records to show that increasing cropland extent and decreasing crop richness were associated with declines in over 50% of bumble bee species in the agriculturally intensive Midwest, USA. Critically, we found that high crop diversity was associated with a higher occurrence of many species pre‐1950 even in agriculturally dominated areas, but that current agricultural landscapes are devoid of high crop diversity. Our findings suggest that insect conservation and agricultural production may be compatible, with increasing on‐farm and landscape‐level crop diversity predicted to have positive effects on bumble bees.

Climate change winners and losers among North American bumblebees

“…By contrast, work done in North America and Europe showed that species are failing to track warming at northern range limits and experiencing range losses at southern range limits [16]. Studies looking at North American bumblebee relative abundances have largely found declines, and are generally consistent with our estimates of declines [7,8,11,13].…”

“…Effects of land use on bumblebee occurrence have been difficult to quantify, particularly at this large scale, and here we show that floral resources might not be the ideal metric. For example, Hemberger et al [11] found that crop diversity, rather than crop extent, was a better predictor of changes in bumblebee occurrence and McArt et al [46] found that fungicide usage was a better predictor of bumblebee decline than land use. Lastly, our floral abundance metric was developed with all bee guilds in mind [35] and, thus, may not be appropriate for bumblebees.…”

“…Several recent studies have made such progress for bumblebees. Hemberger et al [11] found that increasing cropland extent and decreasing crop richness were associated with bumblebee species’ declines in the Midwest, USA, but trends varied among species. Specifically, occurrences of B. terricola , B. fervidus and B. borealis declined with cropland extent, while occurrences of B. affinis , B. bimaculatus and B. impatiens increased.…”

“…Whether insect populations are experiencing global declines is a topic of current debate [1][2][3]. bumblebees are widespread, charismatic and provide critical pollination services to many different flowering plants [4][5][6], and thus their population trajectories are among the most well studied of wild insects [7][8][9][10][11]. Species' trends differ [10], with some in serious decline (e.g.…”

Agriculturally Intensified Landscapes Are Associated With Reduced Body Condition of Lady Beetles

“…However, a mixed diet of complementary foods has been shown to be beneficial for several generalist predators and is actively sought by them (Soares et al 2004;Raubenheimer et al 2007;Harwood et al 2009;Marques et al 2015;Stowe et al 2021a). As such, landscapes with fewer diversity of crops or landscape diversity may manifest as decreases in the physiological condition of mobile predatory arthropods such as lady beetles, leading to longer-term population declines, as has been found for other beneficial insects (Hemberger et al 2021).…”