1

662 known in which insects exposed to short days (but not low temperatures) develop increased cold tolerance, presumably by synthesizing cryoprotectants (Saunders, 2002). Denlinger (1991) concluded that, given the diversity of overwintering strategies found among insects, generalization was not possible. Thus, in some species cold-hardiness occurs in the absence of diapause; in others, diapause and cold-hardiness may occur coincidentally or may be physiologically linked (regulated by the same signals). According to Pullin (1996) there is increasing evidence that the production of polyhydroxyls is linked to the great suppression of metabolic rate which accompanies diapause.

3. Light

Light exerts a major influence on the ability of almost all insects to survive and multiply. A well-developed visual system enables insects to respond immediately and directly to light stimuli of various kinds in their search for food, a mate, a "home," or an oviposition site, and in avoidance of danger (Chapter 12, Section 7). But light influences the biology of many insects in another manner which stems from the earth's rotation about its axis, resulting in a regularly recurring 24-hour cycle of light and darkness, the photoperiod.* Because the earth's axis is not perpendicular to the plane of the earth's orbit around the sun, and because the orbit varies throughout the year, the relative amounts of light and darkness in the photoperiod change seasonally and from point to point over the earth's surface.

Photoperiod influences organisms in two ways: it may either induce short-term (diurnal) behavioral responses which occur at specified times in the 24-hour cycle, or bring about long-term (seasonal) physiological responses which keep organisms in tune with changing environmental conditions. In both situations, however, a key feature is that the organisms that respond have the ability to measure time. In short-term responses the time interval between the onset of light or darkness and commencement of the activity is important. For seasonal responses, the absolute day length (number ofhours of light in a 24-hour period) is usually critical, though in some species it is the day-to-day increase or decrease in the light period that is measured. In other words, organisms that exhibit photoperiodic responses are said to possess a "biological clock," the nature of which is unknown, though its effects in animals are frequently manifest through changes in endocrine activity.

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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