Novel uptake systems for atmospheric water vapor among insects

Abstract

AbstractUptake of water vapor from subsaturated atmospheres in the Psocodea is accomplished by an oral device. During uptake paired lingual sclerites of the ventral hypopharynx are brought into a typical absorbing position. Vapor condensation proceeds onto a fluid layer covering this surface. This fluid presumably originates from a pair of dorsal labial glands. The condensed vapor is transferred from the site of condensation to the entrace of the gut via a sclerotized tubule traversing the hypopharynx. Propulsion of the fluid is achieved by a cibarial sucking pump which operates intermittently. Below the critical equilibrium humidity (CEH) the fluid layer dries up, the salivarium is closed, and uptake of vapor ceases. Uptake of water vapor is a feature common to the whole order Psocoptera and is apparently not related to specific environmental conditions. Among the ectoparasitic descendants from the Psocopteran stock the absorbing system is preserved in both groups of the Mallophaga (Amblycera and Ischnocera); the faculty has, however, been lost independently by single species in both lines. In these species structural components of the uptake device are modified or reduced. The faculty appears to be completely absent in the Anoplura. The distribution of vapor uptake among the Phthiraptera is neither correlated with the type of host nor the mode of nutrition. The CEHs of the Mallophagans (43 to 52% relative humidity: R. H.) are markedly lower than those of the Psocoptera (58 to 85% R. H.). The uptake rates of most Mallophagans are extraordinarily high. A novel case of anal vapor uptake is reported in flea larvae and a preliminary account of rectal structures, possibly involved in vapor uptake, is given.