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THE EVAPORATION OF WATER FROM INSECTS
Author(s) -
MELLANBY KENNETH
Publication year - 1935
Publication title -
biological reviews
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 4.993
H-Index - 165
eISSN - 1469-185X
pISSN - 1464-7931
DOI - 10.1111/j.1469-185x.1935.tb00487.x
Subject(s) - desiccation , humidity , cockroach , biology , relative humidity , saturation (graph theory) , air humidity , insect , transpiration , water vapor , botany , ecology , chemistry , photosynthesis , meteorology , physics , mathematics , organic chemistry , combinatorics
Summary. This article deals with the way in which climatic conditions and insect metabolism affect the rate at which water is evaporated from insects' bodies. It appears that practically all the water evaporated from insects is lost from the tracheal system. At high temperatures the body wall of the cockroach becomes permeable to water. Experimental results may be explained by assuming that when the spiracles are closed, the air in the tracheae is saturated, and in most cases it remains saturated when the spiracles are opened. In some cases, however, particularly in very dry air, the air in the tracheae becomes somewhat dry. The evidence for these suppositions is mainly indirect, but appears reasonably conclusive. The proportion of dry matter in insects, and the ratio of bound water to free, cannot, of themselves, affect the resistance of insects to desiccation. The best protection against desiccation appears to be an efficient mechanism for closing the spiracles, together with the ability to conserve water in the rectum and pass dry excreta. Experiments in which the rate of loss of water is measured in air of various humidities show that the rate is more nearly proportional to the saturation deficiency of the air than to any other measure of humidity. As the temperature rises, the rate of loss at one saturation deficiency sometimes increases, because the insect opens its spiracles more frequently. Experiments to determine the conditions of temperature and humidity which limit survival and breeding of various species support the view that the rate of loss of water is proportional to saturation deficiency. In work of this kind, it is important that results be attributed to the effects of humidity only when humidity alone is the causal factor. The occurrence of optimum temperatures, at which insects can develop over a wider range of humidity than at higher or lower temperatures, is discussed, and a simple explanation is suggested. The ways in which the various environmental and internal factors influence the rate of loss of water are discussed, and the law governing the rate of evaporation of water from insects is stated in a revised form, and its implications are defined.