Evidence for pyroelectric and piezoelectric sensory mechanisms in the insect integument

Quantitative pyroelectric (PE) and piezoelectric (PZE) measurements were carried out on the insect integument of live Blaberus giganteus (cockroach) and on dry integument preparations of the same species. Voltage responses to optical pulses of 10--500 ms, absorbed in the live integument, were PE: interference filter measurements showed the responses to be proportional to the absorbed thermal radiation flux and independent of the wavelength. The voltage/time-course of the responses was in agreement with theoretically calculated PE signals. Voltage responses to mechanical pulses were PZE. The responses of the inner and outer integument surfaces always had opposite electric signs. The polar character of the integument was confirmed by means of a separate dielectric heating method. To explain these results, we hypothesize that the PE properties are for the most part localized in the two outermost layers (outer and inner epicuticle) of the integument, which consists mainly of polar lipids and proteins. Parallel alignment of these polar molecules perpendicular to the integument surface is very likely. PE and PZE responses, therefore, will not only occur in live insects but will also be measurable in dead, dry integument preparations as long as the polar tissue texture remains intact. Due to its polar texture, the insect integument will react to rapid changes in temperature, illumination, or uniaxial pressure in the same way as nonbiological PE materials, where the voltage responses depend on dX/dt (X, pressure or temperature). It seems clear, therefore, that the well-known physiological reactions of various arthropods to such physical outside influences may be related to the PE property of their integument.