A14 Electromagnetic interference

Topic

The insect in flight shares the air with a source of disturbance that did not exist before in its natural environment: the artificial electromagnetic fields generated by high voltage lines, radio frequency emissions and the fields radiated by mobile phones. These artificial electromagnetic fields can interfere with the flight of the insect through several different physical mechanisms, which act in parallel on different parts of the insect itself.

The first of these mechanisms acts directly on the insect's wings: during flight, the wings accumulate triboelectric charges by simple friction with the air, and when the insect passes through an artificial electromagnetic field, the Lorentz force acts on these accumulated charges, pushing them in a way that ends up disturbing the insect's flight path.

The second mechanism does not act on the wings but on the antennae and other conductive structures of the insect: the same artificial electromagnetic field can induce electrical currents within those structures of the insect, and those induced currents generate spurious signals that mix with the real signals within the insect's nervous system, interfering with the information that the insect uses to fly.

The third mechanism acts on the insect in a different way than the previous two: instead of disturbing the trajectory or the nervous system, it depends on how much radiofrequency energy, coming from those same artificial electromagnetic fields, the insect tissue absorbs per unit of mass. When this energy absorbed by the tissue reaches high values, it causes direct heating of the insect tissue and can denature the proteins that compose it, physically damaging the insect instead of only confusing its trajectory or its nervous information.

The most documented mechanism of all, however, acts on the insect in a different way than the previous three: it does not depend on the strength of these fields but on the insect navigating using the Earth's magnetic field as if it were a compass. Bees and flies have magnetoreception, a sense based on biogenic magnetite or cryptochromes, which allows them to orient themselves with respect to that natural magnetic field. When an artificial magnetic field of the order of fifty microteslas—a magnitude comparable to that of the Earth's own magnetic field—is superimposed on this natural compass, the insect is no longer able to clearly distinguish which is the real Earth's field, and this conflict between both magnetic fields generates significant orientation errors in the insect.

How strongly the insect senses any of these four mechanisms—the Lorentz force on wing charges, the induction of spurious currents, tissue heating, or magnetic compass confusion—ultimately depends on how far the insect flies from the source of the artificial electromagnetic field. The intensity of these fields decreases with distance in two combined ways: on the one hand, it decays with the square of the distance once the insect moves far enough from the source, and on the other hand, the medium itself through which the field travels absorbs part of that energy exponentially as the distance increases.

The practical result of these four combined mechanisms is that, near a sufficiently intense source of artificial electromagnetic fields, the insect can see its flight path disturbed, the information traveling through its nervous system interfered, its own tissue damaged, or the magnetic compass with which it normally orients itself confused — and this last alteration is, as documented, the one that most often ends up diverting the insect from the route it needed to follow to fly, migrate or forage correctly.

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