Flower plantings support wild bee reproduction and may also mitigate pesticide exposure effects

Abstract

Sustainable agriculture relies on pollinators, and wild bees benefit yield of multiple crops. However, the combined exposure to pesticides and loss of flower resources, driven by agricultural intensification, contribute to declining diversity and abundance of many bee taxa. Flower plantings along the margins of agricultural fields offer diverse food resources not directly treated with pesticides. To investigate the potential of flower plantings to mitigate bee pesticide exposure effects and support bee reproduction, we selected replicated sites in intensively farmed landscapes where half contained flower plantings. We assessed solitary bee Osmia lignaria and bumble bee Bombus vosnesenskii nesting and reproduction throughout the season in these landscapes. We also quantified local and landscape flower resources and used bee‐collected pollen to determine forage resource use and pesticide exposure and risk. Flower plantings, and their local flower resources, increased O. lignaria nesting probability. Bombus vosnesenskii reproduction was more strongly related to landscape than local flower resources. Bees at sites with and without flower plantings experienced similar pesticide risk, and the local flowers, alongside flowers in the landscape, were sources of pesticide exposure particularly for O. lignaria. However, local flower resources mitigated negative pesticide effects on B. vosnesenskii reproduction. Synthesis and applications. Bees in agricultural landscapes are threatened by pesticide exposure and loss of flower resources through agricultural intensification. Therefore, finding solutions to mitigate negative effects of pesticide use and flower deficiency is urgent. Our findings point towards flower plantings as a potential solution to support bee populations by mitigating pesticide exposure effects and providing key forage. Further investigation of the balance between forage benefits and added pesticide risk is needed to reveal contexts where net benefits occur.

Ecological traits interact with landscape context to determine bees’ pesticide risk

“…Using our trait-based approach, we conclude that landscape context modifies pesticide risk but only for limited and intermediate foragers (here, O. bicornis and B. terrestris, respectively). These findings highlight the potential for seminatural habitats to buffer pesticide-related risks for wild bees 26,46,66 . We also conclude that A. mellifera-collected pollen can predict environmental pesticide risk for other species and is precautionary, particularly in less agriculturally dominated landscapes.…”

“…Our use of O. bicornis as a sentinel allowed us to estimate exposure and risk of a limited forager in landscapes where they may not naturally occur, which, combined with the relatively generalised diet of Osmia spp. 26,48,50 , means that our estimates for limited foragers are probably precautionary among solitary bee species.…”

“…The pesticide exposure of bees arises from their activity intersecting pesticide use 12 . Thus, pesticide exposure and its correlated risk (additive toxicity-weighted concentrations) to bees are likely to be affected by their life-history traits 37 , particularly foraging habits 23 , 26 , 38 and land-use and pesticide-use patterns, especially in bee-attractive crops 39 , 40 . Using an ecological approach to pesticide risk, we found that extensive foragers ( A. mellifera ) experienced the greatest risk irrespective of the proportion of agricultural land in the landscape.…”

“…Thus, seminatural habitats that could provide refuge from pesticides are more likely to be potential sources of exposure in intensively managed agricultural landscapes 22 . As central place foragers, the reproduction of bees depends on the density and value of food resources within their foraging range [23][24][25][26] and the proportion of the foraging range of a bee affected by pesticide use should correlate to their pesticide exposure 15,27,28 .…”

Experimental heatwaves disrupt bumblebee foraging through direct heat effects and reduced nectar production

“…Most bumblebee colonies maintain only a few days of food reserves (Couvillon & Dornhaus, 2010) and an extended heatwave could exacerbate food limitation and create resource bottlenecks (Maron et al, 2015; Schellhorn et al, 2015), especially in landscapes with limited resources (Samuelson et al, 2018). Extended heatwaves may also negatively synergize with other stressors such as pesticide use (Goulson et al, 2015; Kenna et al, 2019; Rundlöf et al, 2022; Stuligross & Williams, 2020) and land‐use change (Hemberger et al, 2021; Marshall et al, 2018). Alarmingly, the time of year when heatwaves are most likely to push temperatures above thermal optima corresponds with periods of reduced resource abundance, typically in early and late summer (Timberlake et al, 2019), although larger colonies may be more able to handle short‐term reductions in foraging given food stores (Heinrich, 2004).…”