The Abiotic Environment

diapause. In Mansingh's scheme the final phase of diapause is the termination phase, which 671

occurs when environmental conditions become favorable for development. In this phase the metabolic rate returns to normal, the endocrine system once more becomes active, body tissues again become capable of nucleic acid and protein synthesis, and any cryoprotectants present gradually disappear. As a result of these changes postdiapause development can begin.

In view of the varying degrees of severity of climatic conditions that insects in different geographic regions may encounter, it is perhaps not surprising to find that the intensity (duration and stability) of diapause varies. This variability, which is both interspecific and intraspecific, is manifest as a broad spectrum of dormancy that ranges from a state virtually indistinguishable from quiescence ("weak" or "shallow" diapause) to one of great stability ("strong" or "intense" diapause) in which an insect can resist extremely unfavorable conditions. In each situation the strength of diapause is precisely adjusted through natural selection to provide an insect with adequate protection against the adverse conditions, yet to continue growth and reproduction as soon as an amenable climate returns. Broadly speaking, insects from less extreme climates show weak diapause [called oligopause by Mansingh (1971)], in which development may not be completely suppressed; the insects may continue to grow slowly (and even molt) and feed when conditions permit during the period of generally adverse climate. In weak diapause the induction phase is relatively short, since the biochemical adjustments that an insect makes in order to cope with the adverse conditions are relatively simple. As a corollary of this, insects that overwinter in weak diapause are not, for example, very cold-tolerant. The refractory phase is short so that the activated phase is entered relatively soon after diapause has begun, and diapause is quickly terminated when environmental conditions return to normal. Conversely, in strong diapause, which is the rule in insects from severe climates, there is a lengthy induction phase, after which development is fully suppressed. The refractory phase usually lasts for several weeks or months, and the activated phase usually does not begin until diapause is more than half over. The termination phase is relatively slow, normally spanning 2 or 3 weeks after the return of suitable climatic conditions. Frequently insects that overwinter in strong diapause are very cold-hardy.

Diapause was formerly subdivided into facultative and obligate diapause. Facultative diapause described the environmentally controlled diapause of bivoltine and multivoltine species (having two or more generations per year) in which the members of certain generations had no diapause in their life history. Obligate diapause referred to the diapause found in univoltine species (those with one generation per year) in which every member of the species undergoes diapause. It was incorrectly assumed that in univoltine species diapause was not induced by environmental factors. However, experimental work on a number of univoltine species has revealed that in these species diapause is environmentally controlled. Further study may well demonstrate that this is always the case and render invalid the distinction between obligate and facultative diapause.

Induction, Maintenance, and Termination. Various factors may influence the course of diapause. Photoperiod is especially important in the induction of diapause, though ambient temperatures, population density, and diet during the preparatory and induction phases may influence the incidence (proportion of individuals entering diapause) and intensity of dormancy. For many species photoperiod is also important, though temperature plays an increasing role, either alone or in combination with photoperiod, in diapause maintenance. Examples of both hibernating and estivating species that require a specific photoperiod to terminate diapause are also known.

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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