Postembryonic Development

affect growth rates and the frequency of ecdysis that the law is frequently inapplicable. In any event, the law requires that the interval between molts remains constant, but this is rarely the case.

As winged insects grow, they change shape; that is, the relative proportions of different parts of the body change. This disproportionate growth, which is not unique to insects, is described as "allometric" (heterogonic, disharmonic). In other words, each part has its own growth rate, expressed by the equation y = bxk (y = linear size of the part, x = linear size of the standard (e.g., body length), b = initial growth index (y intercept), and k = allometric coefficient). Normally, allometric growth is expressed as a log-log plot, when k is the gradient of the slope (Figure 21.3).

Growth laws do not apply in situations where the number of instars is variable. This variability may be a natural occurrence, especially in primitive insects such as mayflies that have many instars. In addition, females that are typically larger than males may have a greater number of instars than males. Variability may also be induced by environmental conditions. For example, rearing insects at abnormally high temperature often increases the number of instars, as does semistarvation. In contrast, in some caterpillars crowding leads to a decrease in the number of molts.

Caterpillars and probably other larvae whose cylindrical body is covered with a thin integument rely on hydrostatic (hemolymph) pressure to maintain the rigidity necessary for locomotion. However, this presents a problem with respect to their body form during growth. Mechanically, in a cylinder under internal pressure the hoop stress (around the body) is twice the axial (lengthwise) stress. Thus, a caterpillar theoretically should become proportionately fatter as it grows, much like a balloon when inflated. That it does not do

FIGURE 21.3. Allometric growth in Carausius (Phasmida). [After V. B. Wigglesworth, 1965, The Principles of Insect Physiology, 6th ed., Methuen and Co. By permission of the author.]

so is due to the occurrence of axial pleats (transverse cuticular folds) that reduce the axial stress by unfolding as the insect enlarges (Carter and Locke, 1993).

Beekeeping for Beginners

Beekeeping for Beginners

The information in this book is useful to anyone wanting to start beekeeping as a hobby or a business. It was written for beginners. Those who have never looked into beekeeping, may not understand the meaning of the terminology used by people in the industry. We have tried to overcome the problem by giving explanations. We want you to be able to use this book as a guide in to beekeeping.

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