Survival at Extreme Temperatures

In many tropical areas climatic conditions are suitable for year-round development and reproduction in insects. In other areas of the world, the year is divisible into distinct seasons, in some of which growth and/or reproduction is not possible. One reason for this arrest of growth and/or reproduction may be the extreme temperatures that occur at this time and are potentially lethal to an insect. In many instances shortage of food would also occur under these conditions.

To avoid the detrimental effects of periods of moderately low (down to freezing) or high temperature, and to ensure that development and reproduction occur at favorable times of the year, insects use an array of behavioral and physiological mechanisms (Danks, 2001,2002). First, the life history of many species is arranged so that the period of adverse temperature is passed as the immobile, non-feeding egg or pupa. Second, prior to the advent of adverse conditions [and it should be realized that the token stimulus that triggers this behavior is not, in itself, adverse (see Section 3.2)], an insect may actively seek out a habitat in which the full effect of the detrimental temperature is not felt. For example, it may burrow or oviposit in soil, litter, or plant tissue, which acts as an insulator. Third, it may enter diapause where its physiological systems are largely inactive and resistant to extremes of temperature.

2.4.1. Cold-Hardiness

Cold-hardiness refers to an insect's ability to adapt to and survive low temperatures. Some insects are "chill-intolerant," that is, suffer lethal injury even at temperatures above 0° C. Others are "chill-tolerant," though a period of gradual temperature acclimation (hardening) may be required for tolerance to develop (Bale, 1993, 1996; S0mme, 1999). For insects in environments that experience temperatures below 0°C, an additional problem presents itself, namely, how to avoid being damaged by freezing of the body cells. The formation of ice crystals within cells causes irreversible damage to and frequently death of an organism (1) by physical disruption of the protoplasm and (2) by dehydration, reduction of the liquid water content that is essential for normal enzyme activity. Insects that survive freezing temperatures are described as either freezing-susceptible or freezing-tolerant. Freezing-susceptible species are those whose body fluids have a lower freezing point and may undergo supercooling. Freezing-tolerant (= freezing-resistant = frost-resistant) species are ones whose extracellular body fluids can freeze without damage to the insect.

In both groups, two or three types of cryoprotectants (substances that protect against freezing) are produced. Cryoprotectants identified to date fall into three categories: (1) ice-nucleating agents (proteins), produced only in freezing-tolerant species; (2) low-molecular-weight polyhydroxyl substances such as proline, glycerol, sorbitol, mannitol, threitol, sucrose and trehalose; and (3) thermal-hysteresis or antifreeze proteins (Duman and Horwath, 1983; Lee, 1991; Bale, 2002). Typically, insects produce two or more polyhydroxyls. This may be because they are toxic at higher concentrations, an effect that can be avoided by the use of a multicomponent system.

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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