Volume of Hemolymph

The hemolymph in an insect varies with the species, the diet, the age, the state of hydration and the methods used to measure its volume. Exsanguination, dye dilution methods and C14 inulin are the most common ways of measuring the volume of hemolymph.

A bee's volume of hemolymph may be expressed as a percentage of the weight of her body. This percentage of an insect's weight varies with the type of insect and its state of hydration. Generally, hemolymph forms between fifteen to seventy percent of an insect's weight. Consider the hemolymph of an insect as being about 26% of its body weight, a percentage that is greater than the percent of blood volume in vertebrates.

Hemolymph is a reservoir for water. The water in hemolymph is about one-quarter of the bee's total body water. As an example of volumes, one can remove about 0.01 microliters of fluid from a honeybee and about 20,000 microliters from a large queen termite. Some insects appear, however, to possess very little hemolymph in their bodies when attempts are made to extract it from the hemocoel. In general, the smaller the insect, the smaller the volume of hemolymph relative to the size of the hemocoel, but to my knowledge, careful modern comparative studies of this important relationship in large and small insects do not yet exist. One example of a large insect having a small volume of hemolymph is the periodical cicada, Magicicada sp. We expect, however, to find low volumes of hemolymph in the smallest forms, as the three-dimensional volume of hemolymph in larger forms shrinks down to become a moistened two-dimensional layer lining the external surfaces of the organs and the inner surfaces of the hemocoel in the smallest insects. A smaller volume of hemolymph reduces weight and should increase the probability of transport within the hemocoel by diffusion (Chapter 9).

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