Differential sensitivity of honey bees and bumble bees to a dietary insecticide(imidacloprid)

• Currently, there is concern about declining bee populations and the sustainability of pollination services.One potential threat to bees is the unintended impact of systemic insecticides, which are ingested bybees in the nectar and pollen from flowers of treated crops. To establish whether imidacloprid, a systemicneonicotinoid and insect neurotoxin, harms individual bees when ingested at environmentally realisticlevels, we exposed adult worker bumble bees, Bombus terrestris L. (Hymenoptera: Apidae), and honeybees, Apis mellifera L. (Hymenoptera: Apidae), to dietary imidacloprid in feeder syrup at dosages between0.08 and 125 g l−1. Honey bees showed no response to dietary imidacloprid on any variable that wemeasured (feeding, locomotion and longevity). In contrast, bumble bees progressively developed overtime a dose-dependent reduction in feeding rate with declines of 10–30% in the environmentally relevantrange of up to 10 g l−1, but neither their locomotory activity nor longevity varied with diet. To explaintheir differential sensitivity, we speculate that honey bees are better pre-adapted than bumble bees tofeed on nectars containing synthetic alkaloids, such as imidacloprid, by virtue of their ancestral adaptationto tropical nectars in which natural alkaloids are prevalent. We emphasise that our study does not suggestthat honey bee colonies are invulnerable to dietary imidacloprid under field conditions, but our findingsdo raise new concern about the impact of agricultural neonicotinoids on wild bumble bee populations.

Nyckelord

Apis mellifera

Bombus terrestris

Detoxification

Neonicotinoid

Toxic nectar

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