Abstract
Simple SummaryHoneybees are important pollinators, and may contribute to the spread of plant bacteria during their foraging trips. Some of these bacteria, such as Pantoea ananatis, can become deleterious to crops, leading to leaf blotches, die-back, bulb rot, and fruit rot. It is unknown whether honeybees sense the bacteria in the nectar of flowers. We aimed to determine if bees can perceive these bacteria in sugar solutions and if they are deterred by them. Our results indicate that honeybees can perceive these plant bacteria only in high concentrations, which deters them from drinking the respective sugar solution. They may therefore spread P. ananatis bacteria between flowers in field-realistic densities during foraging.1. Honeybees, which are among the most important pollinators globally, do not only collect pollen and nectar during foraging but may also disperse diverse microbes. Some of these can be deleterious to agricultural crops and forest trees, such as the bacterium Pantoea ananatis, an emerging pathogen in some systems. P. ananatis infections can lead to leaf blotches, die-back, bulb rot, and fruit rot. 2. We isolated P. ananatis bacteria from flowers with the aim of determining whether honeybees can sense these bacteria and if the bacteria affect behavioral responses of the bees to sugar solutions. 3. Honeybees decreased their responsiveness to different sugar solutions when these contained high concentrations of P. ananatis but were not deterred by solutions from which bacteria had been removed. This suggests that their reduced responsiveness was due to the taste of bacteria and not to the depletion of sugar in the solution or bacteria metabolites. Intriguingly, the bees appeared not to taste ecologically relevant low concentrations of bacteria. 4. Synthesis and applications. Our data suggest that honeybees may introduce P. ananatis bacteria into nectar in field-realistic densities during foraging trips and may thus affect nectar quality and plant fitness.
Highlights
Many insects such as honeybees (Apis mellifera) are important pollinators globally
Sugar concentrations were contaminated (Table 1, Figure 1). This effect of bacterial density in the sugar solution on proboscis extension responses (PERs) was observed in both pollen and nectar foraging bees (Table 1, Figure 1) to a similar extent. These experiments demonstrate that honeybees are deterred by high bacterial density of P. ananatis in a sugar solution, when they sense the bacteria with their antennae
Our experiments clearly show that honeybees are capable of perceiving P. ananatis bacteria when the bacteria are offered to their antennae in high concentrations in sugar solutions
Summary
Many insects such as honeybees (Apis mellifera) are important pollinators globally. About 75% of major field crops, fruits, and vegetables produced for human consumption require insect pollination [1].the vast majority of wild plants depend on insect pollination [2,3]. Many insects such as honeybees (Apis mellifera) are important pollinators globally. About 75% of major field crops, fruits, and vegetables produced for human consumption require insect pollination [1]. The vast majority of wild plants depend on insect pollination [2,3]. Honeybees are among the most efficient pollinators, not least due to their large colony size. They collect nectar, pollen, and resin from diverse plants. During their visits to flower blossoms, bees frequently come in contact with
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