EVIDENCE FOR HYDRATION-DEPENDENT CLOSING OF PORE STRUCTURES IN THE CUTICLE OF PERIPLANETA AMERICANA

Integumental electrical resistances were measured on the antenna, pronotum, forewing, second abdominal tergite, fifth abdominal sternite and the femur of the third leg in restrained male and female Periplaneta americana. The same measurements, excepting those on antenna and wing, were made on last-instar nymphs. Electrical contact was made through two externally applied glass tubes filled with cockroach Ringer with a combined contact area of about 2 mm2. Resistances corresponding to current flows through two thicknesses of integument were measured using a current-clamping amplifier. Calculated electrical conductances tended to be higher in the antennae, pronotum and abdominal tergites than in the legs and wings. Conductances of the pronotum and abdominal tergites were significantly higher (P<0.001) in males than in females. The literature suggests that male abdominal tergites are the site of sex pheromone production. In nymphs as well as adults, the conductances of all areas, except the antennae of males, decreased following dehydration and a decline in animal water content. In most cases the magnitude of the decrease was tightly correlated with initial hydrated conductance. The data suggest that variations in regional conductances in hydrated animals are principally due to differences in dermal gland density. We argue that the decrease in conductance following dehydration is evidence of a mechanism closing dermal gland openings in times of water stress.