Glyphosate-based herbicide increases the number of foraging trips but does not affect the homing of Bombus terrestris

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Abstract
The intensification of pesticide use is believed to be one of the main causes of the global decline in pollinators. The ability to forage resources effectively and return to the colony is crucial for individual eusocial bees and their colonies, and some pesticides are known to disturb this ability. Our study investigated the effects of the most widely used type of pesticide, glyphosate-based herbicides (GBHs), on the foraging and homing ability of the buff-tailed bumblebee, Bombus terrestris (L.) (Hymenoptera: Apidae). We conducted two experiments in which we exposed bees to field-realistic doses of GBH at colony and/or individual levels and observed their foraging activity and the homing ability of displaced bees. We found that 24-h colony-level GBH exposure increased the number of bumblebees’ foraging bouts, but it did not affect the duration of bouts or the homing ability. Regarding the homing rate, there was a marginally significant interaction between acute individual-level treatment and release distance from the colony. Even though the negligible impacts of short-term GBH exposure on homing ability are encouraging, the greater number of (possibly unnecessary) foraging bouts after colony-level GBH exposure might be costly for bumblebees.
Funding Information
  • Research Council of Finland (311077)
  • Suomen Kulttuurirahasto
  • Novo Nordisk Fonden (NNF0093951)
  • University of Turku

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