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Experiments were carried out to investigate the effects of fluctuating low-level magnetic fields on the demography and behaviour of Rhyzopertha dominica (F.). Adult insects were exposed to low-level magnetic fields, generated from both full- and half-wave rectified power supplies at 50 Hz and with magnetic-field strengths of 2–4 times that of the earth. Significant insect responses, in terms of changes to fecundity, development period and aspects of behaviour, were observed in many of the experiments and the nature of the response depended upon the power supply generating the magnetic field used. There appeared to be a dose effect because the reduction in progeny production diminished with distance from the centre of the field and the effects upon fecundity were cumulative. Numbers of progeny produced declined steadily over a 5-week period of exposure to the magnetic field, contrasting with the control which increased over the same period. The behavioural experiments showed that, despite a marked position effect within the experimental room, the magnetic field clearly had a deterrent effect upon the insects. The complex nature of the observed responses is discussed in relation to measured differences between the power supplies used in the experiments. The general issue of experimental methodology in such studies is also explored. |
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