The effects of exposure of honey bees to a 50 Hz magnetic field on aversive learning and the aggression level should be investigated.
Honey bees, Apis mellifera, are a significant pollinator species and are currently in decline. Environmental stressors, like ELF MF, are suspected of being a reason for this. Therefore, the effects of ELF MF on aversive learning and aggression levels were investigated in this study, as they are critical factors for bees to maintain colony strength.
Bees were divided into the following groups: exposure to a magnetic field of 1) 100 µT, 2) 1000 µT oder 3) sham exposure.
The sting extension response assay for testing aversive learning, was completed by a total of 357 bees: n=118 in group 1, n=120 in group 2 and n=119 in group 3 (remark EMF-Portal: the initial numbers of bees which entered the test are not clear). In the intruder assay for testing of the aggression level, bees were collected from 5 different hives in groups of 20 bees from the same hive of origin. Each group of 20 was split into 2 paired subgroups of 10. One subgroup of each pair was exposed to the 100 µT magnetic field (group 1) and the other one was sham exposed (group 3). No exposure to the 1000 µT magnetic field was conducted for this test. In total 60 intruder assay samples were conducted (n = 30 per treatment, with 6 assays/treatment/hive).
| Exposure | Parameters |
|---|---|
|
Exposure 1:
50 Hz
Exposure duration:
17 hours
|
|
|
Exposure 2:
50 Hz
Exposure duration:
17 hours
|
|
| Frequency | 50 Hz |
|---|---|
| Type | |
| Waveform | |
| Exposure duration | 17 hours |
| Exposure source | |
|---|---|
| Setup | in the intruder assay, bees were exposed in petri dishes over night at 22 ± 1˚C |
| Sham exposure | A sham exposure was conducted. |
| Additional info | for sham exposure no current was passed through the coil system |
| Measurand | Value | Type | Method | Mass | Remarks |
|---|---|---|---|---|---|
| magnetic flux density | 100 µT | - | measured | - | - |
| Frequency | 50 Hz |
|---|---|
| Type | |
| Waveform | |
| Exposure duration | 17 hours |
| Exposure source |
|
|---|
| Measurand | Value | Type | Method | Mass | Remarks |
|---|---|---|---|---|---|
| magnetic flux density | 1,000 µT | - | measured | - | - |
Exposure to both the magnetic field of 100 μT (group 1) and 1000 μT (group 2) significantly reduced the aversive learning performance. Moreover, exposure to the 100 µT magnetic field (group 1) significantly increased aggression scores.
The authors conclude that exposure of honey bees to a 50 Hz magnetic field might reduce aversive learning and increase the aggression level, which might have ecological implications for bees in nature.
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