The Effects of Nectar–Nicotine on Colony Fitness of Caged Honeybees

Abstract

Abstract-Nectar of many bee flowers contains secondary compounds, which are considered toxic for honeybees on repeated exposure. Although many anecdotal reports indicate the toxicity of secondary compounds to bees, only a few studies have tested the extent of toxicity at different honeybee ages, especially at the larval stages. Honeybees encounter nicotine at trace concentrations (between 0.1 and 5 ppm) in floral nectar of a few Nicotiana spp. and in Tilia cordata. Adult honeybee workers tolerate these nicotine concentrations. In controlled nonchoice feeding experiments with caged bees, we investigated the effect of nicotine on hatching success and larval and forager survival. Naturally occurring concentrations of nectar-nicotine did not affect hatching success of larvae or their survival, but the latter was negatively affected by higher concentrations of nicotine (50 ppm). Concentrations of nicotine in fresh honey samples from the hives were 90% lower than the concentrations in the offered experimental sucrose solutions. Our results indicate that honeybees can cope with naturally occurring concentrations of nicotine, without notable mortality, even when consumed in large quantities for more than 3 weeks.

Resistance of developing honeybee larvae during chronic exposure to dietary nicotine

“…The lack of consistent, negative effects of nicotine on the survival of developing honeybee larvae supports previous studies showing limited effects of nicotine in sucrose solutions on survival of caged workers (Köhler et al, 2012a) and on hatching success and survival of honeybee larvae in 'minihives' maintained in enclosures (Singaravelan et al, 2006). The latter authors, however, found that 50 ppm nicotine reduced larval survival, with the highest mortality in day 3 larvae: this is 5x higher than the highest concentration in our experiments.…”

“…Previously, we have found that survival of caged Apis mellifera scutellata workers was unaffected by 30 µM (5 ppm) nicotine in sucrose diets, and actually improved in the case of weak colonies (Köhler et al, 2012a). At the colony level, Singaravelan et al (2006) fed honeybees nicotine in sucrose solutions for 26 days: hatching success and larval survival were not affected by nicotine levels up to 30 µM, which can occur naturally in floral nectar of Nicotiana species (Adler et al, 2012). …”

Protein and alkaloid patterns of the floral nectar in some solanaceous species

“…In the nectar of N. attenuata the concentration of nicotine was 3 ± 0.35 µg/mL [13]. The mean concentrations of nicotine measured by us in the nectar of N. alata and N. rustica were within the range of 0.79-2.5 µg/mL which was found to be attractive and even addictive for honeybees [55], whereas nicotine concentrations in N. tabacum nectar slightly exceeded 5 µg/mL, which can already have aversive effect. In a different study, adult honeybee workers and even their larvae were reported to tolerate naturally occurring nectar nicotine-concentrations (0.1-5 µg/mL), with no disadvantageous effect on their emergence success and survival [45].…”

“…Due to their detoxificating enzymes, honeybees show physiological plasticity against pesticides and special floral metabolites [56,59]. However, a higher nicotine concentration (50 µg/mL) was found to cause the post-emergence mortality of the larvae [55]. In another set of honeybee feeding experiments [28] the ED 50 value (the concentration of alkaloid which caused 50% of the maximal possible effect) for both nicotine and scopolamine was determined as 0.3 µg/mL, i.e.…”

“…However, by using modern analytical techniques such as gas chromatography (GC) and high performance liquid chromatography (HPLC), a number of researchers have already succeeded in identifying as well as quantitatively determining the characteristic alkaloids in the floral nectar of various Solanaceae species [3, 13, 17, 28-29, 44, 57]. Some of these alkaloids, like hyoscyamine, scopolamine, tropin, nicotine and anabasine were reported to cause feeding deterrence to animal pollinators [28,55,57]. Alkaloids, along with some non-protein amino acids and phenolic components, belong to the most common nectar toxins [52].…”