Floral resource diversification promotes solitary bee reproduction and may offset insecticide effects – evidence from a semi‐field experiment

Abstract

Pollinator declines in agricultural landscapes are driven by multiple stressors, but potential interactions of these remain poorly studied. Using a highly replicated semi‐field study with 56 mesocosms of varying wild plant diversity (2–16 species) and oilseed rape treated with a neonicotinoid, we tested the interacting effects of resource diversity and insecticides on reproduction of a solitary wild bee. Compared to mesocosms with oilseed rape monocultures, availability of resources from wild plants complementing oilseed rape doubled brood cell production. In addition, bee reproduction increased due to plant diversity and identity effects. Exposure to neonicotinoid‐treated oilseed rape reduced bee larval to adult development by 69%, but only in mesocosms with oilseed rape monocultures. Availability of complementary flower resources can thus offset negative effects of neonicotinoid‐treated oilseed rape on wild bee reproduction. Policy should encourage the implementation of diverse floral resources mitigating negative effects of crop monocultures and insecticides, thereby sustaining solitary bee populations in agricultural landscapes.

Supplemental forage ameliorates the negative impact of insecticides on bumblebees in a pollinator-dependent crop

“…It was particularly striking that survival was 100% in all three treatments with zero or one stressor alone, but the combination of two stressors caused survival to plummet to 17%. These data suggest that cultivating or encouraging supplemental flowers in and around crop fields can buffer the negative non-target effects from insecticides [ 14 , 16 ]. In the field, growers could accomplish this by implementing wildflower strips along field borders or adopting a less stringent herbicide regime to encourage flowering weeds.…”

“…The presence of natural habitat in the landscape is known to buffer the negative effects of insecticide use [ 13 , 14 ]. However, few studies have experimentally manipulated supplemental forage and insecticide use in tandem (but see [ 15 , 16 ]), and these mostly employ controlled laboratory experiments that do not resemble a natural foraging arena [ 17 , 18 ]. Virtually, all of the existing work in this area also employs artificial feeders that titrate insecticides or nutritional resources via sugar water rather than simulating actual exposure routes and concentrations that a bee encounters while foraging in the field [ 19 ].…”

Pollinators and plant nurseries: how irrigation and pesticide treatment of native ornamental plants impact solitary bees

“…In the field, a bee's foraging range might encompass plants both with and without pesticides. Available alternative forage can diminish the impacts of neonicotinoids on solitary bees [ 13 ]. However, previous work on wild bee foraging in nurseries suggests high day-to-day fidelity to floral patches [ 6 ].…”

“…Relevant in-field management practices for bees in any agricultural area include those affecting vegetation quality, agrochemical input, and soil characteristics [ 11 ]. Interactions between local management practices, such as whether one mitigates or exacerbates the effects of another, are only recently being investigated using manipulative experiments [ 12 , 13 ].…”

“…Multiple factors influence the amount of these systemic insecticides entering pollen and nectar of ornamental plants [ 15 , 16 ], but we have a poor understanding of these factors and how they interact [ 17 ]. Recent studies revealed that increased local floral resource availability may buffer against some negative impacts of pesticide exposure in solitary bee populations [ 12 , 13 ]. However, supplementation of floral resources [ 11 ] for bees is unlikely to be financially incentivizing in nurseries, as most ornamental crops rarely require pollination services.…”