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Medical/biological study (experimental study)

Extremely Low Frequency Electromagnetic Fields impair the Cognitive and Motor Abilities of Honey Bees.

Published in: Sci Rep 2018; 8 (1): 7932

Aim of study (acc. to author)

To investigate how acute exposure of honey bees to 50 Hz magnetic fields occurring near high-voltage power lines affects learning and memory, motor ability, foraging activity and feeding.
Background/further details: Three experiments were conducted:
For the first experiment, to examine learning and memory, 438 immobilized bees were used in total and divided into four exposure groups: 1a) sham exposure (n=114), 1b) 20 µT magnetic field (n=111), 1c) 100 µT magnetic field (n=106) and 1d) 1000 µT magnetic field (n=107).
In the second experiment, the wing beat frequency in tethered bees was determined. The following groups were examined (n=30 per group): 2a) sham exposure, 2b) 100 µT magnetic field, 2c) 1000 µT magnetic field or 2d) 7000 µT magnetic field.
The third experiment examined foraging activity and feeding in 2,919 bees and took place in an arena with the hive on one side and the feeder on the other side. After 30 minutes for adaption and locating the feeder, 15 minutes baseline behavior were recorded. Then, behavior was recorded during 15 minutes of exposure to a 100 µT magnetic field or sham exposure. Seven days later, the experiment was repeated. Bees that had been sham exposed in the first trial were now magnetic field-exposed and vice versa.

Endpoint

Exposure

Exposure Parameters
Exposure 1: 50 Hz
Exposure duration: 1 minute (4 times between the 5 conditioning trials)
Exposure 2: 50 Hz
Exposure duration: 2.5 seconds
Exposure 3: 50 Hz
Exposure duration: 15 minutes
General information
A magnetic field present in the environment at a pylon of a 400 kV transmission line was replicated in the laboratory.
Exposure 1
Main characteristics
Frequency 50 Hz
Type
Waveform
Exposure duration 1 minute (4 times between the 5 conditioning trials)
Exposure setup
Exposure source
Setup magnetic field was generated by custom-made paired coils with an inner diameter of 25 cm; coils were fixed 14 cm apart
Sham exposure A sham exposure was conducted.
Additional info for sham exposure, no current was passed through coils
Parameters
Measurand Value Type Method Mass Remarks
magnetic flux density 20 µT - measured - -
magnetic flux density 100 µT - measured - -
magnetic flux density 1,000 µT - measured - -
Exposure 2
Main characteristics
Frequency 50 Hz
Type
Waveform
Exposure duration 2.5 seconds
Exposure setup
Exposure source
Sham exposure A sham exposure was conducted.
Parameters
Measurand Value Type Method Mass Remarks
magnetic flux density 100 µT - measured - -
magnetic flux density 1,000 µT - measured - -
magnetic flux density 7,000 µT - measured - -
Exposure 3
Main characteristics
Frequency 50 Hz
Type
Waveform
Exposure duration 15 minutes
Exposure setup
Exposure source
Setup same set-up as in exposure 1, but coils were fixed 20 cm apart
Sham exposure A sham exposure was conducted.
Parameters
Measurand Value Type Method Mass Remarks
magnetic flux density 100 µT - measured - -
Exposed system:

Methods Endpoint/measurement parameters/methodology

  • cognitive/behavioral endpoints: learning and memory (proboscis extension reflex in an arena after being conditioned with an odour stimulus and sugar solution); motor abilities (wing beat frequency 0.5 seconds before and 2.5 seconds after exposure began, video recording); foraging (number of succesful flights, i.e., flights from one side of the arena (hive) to the other (feeding place) and back) and feeding (number of bees feeding every minute) (video recording)
Investigated material:
Time of investigation:
  • before exposure
  • during exposure
  • after exposure

Main outcome of study (acc. to author)

In the first experiment, exposed bees (groups 1b, 1c, 1d) showed significantly impaired learning acquisition and memory abilities compared to the sham exposed ones (group 1a). With higher magnetic flux densities (100 µT (group 1c) and 1000 µT (group 1d)), this effect was significantly more pronounced with no significant differences between group 1c and 1d.
In the second experiment, the wing beat frequency was higher with increasing magnetic flux density, reaching statistically significant values in the group exposed to a magnetic flux density of 7000 µT (group 2d) when compared to sham exposure (group 2a).
In the third experiment, the number of successful outgoing passes was significantly decreased in exposed bees compared to the sham exposed ones. Additionally, the number of feeding bees per minute was reduced in exposed bees compared to sham exposed ones reaching statistical significance after 10 minutes and more of exposure.
The authors conclude that the results suggest that 50 Hz magnetic fields occurring near high voltage transmission lines could affect learning and memory, motor ability, foraging activity and feeding in bees, which could in turn reduce their crop pollination ability.
Study character:

Study funded by

  • Fundacao de Amparo à Pesquisa do Estado de Minas Gerais (FAPEMIG), Brazil
  • University of Southampton, UK
  • Science without Borders (Ciência sem Fronteiras, Brazil)

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