Polymorphism

Polymorphism, the existence of several distinct forms of the same life stage of an organism, though not a common phenomenon in insects, occurs in representatives of several widely different orders. The phases of locusts (Orthoptera) and some caterpillars (Lepidoptera), castes of social insects (Isoptera and Hymenoptera), wing polymorphism in crickets (Orthoptera), aphids and other Hemiptera, and color polymorphism of mimetic butterflies (Lepidoptera) are examples of insect polymorphism. Though these examples refer only to difference of form, it should be appreciated that the physiology, behavior, and ecology of these forms are also different (Applebaum and Heifetz, 1999).

Polymorphism, like differentiation, has a genetic basis. In some examples of polymorphism, such as the color forms of butterflies and moths, the genetic system is relatively little influenced by short-term changes in environmental conditions. This so-called "genetic (obligate) polymorphism" includes transient polymorphism, the situation in which a trait is spreading through a population (e.g., melanism in the peppered moth, Biston betularia), and balanced polymorphism where a trait is maintained at a constant frequency in the population by opposing selection pressures [e.g., mimicry by the (edible) viceroy butterfly of the (distasteful) monarch butterfly (Figure 9.15)]. At the opposite extreme is "phenotypic (facultative) polymorphism" (now commonly referred to as "polyphenism") in which the development of characters is greatly influenced by changing environmental conditions and is manifest within a few generations (e.g., caste polymorphism, phase polymorphism, and wing polymorphism). The changing environmental conditions exert their influence via the neuroendocrine system; in other words, it is changes in the hormonal milieu that lead to polyphenism, particularly changes in the level of JH, as will be shown in the examples described below (Nijhout and Wheeler, 1982).

Aphid polymorphism is a complex phenomenon for, in addition to extensive structural polymorphism (some species include as many as eight distinct forms) (Figure 21.15) and the physiological polymorphism that accompanies it, there is also "temporal" or "successive"

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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