Evidence Against Hormonal Control of Integumentary Water Loss in Periplaneta Americana

The effect of decapitation on water loss from adult male cockroaches was studied in order to re-examine the possibility of hormonal modulation of integumental permeability. We found no effect of decapitation on the permeability or water content in measurements made on the pronotum. Although overall weight losses of the decapitated animals always exceeded those of intact animals, loss rates and their rate of decline depended on the apparent severity of handling. There was a small but significant difference between the controls and all decapitated and sham-operated animals, and this difference persisted for at least 96 h. We attribute these results principally to the differential effects of cuticle damage, though increased respiratory water loss may also be a factor. Our results draw attention to the complex practical problems involved in obtaining accurate, representative cuticle permeabilities for Periplaneta, and form a basis for questioning the notion of inhibition of cuticular water loss by hormones from the head.