The Abiotic Environment

surface area is relatively large in relation to body volume. That insects have been able to 675

solve this problem is one of the main reasons for their success as a terrestrial group. Not only do insects generally possess a highly impermeable cuticle (Chapter 11, Section 4.2) and various devices for reducing water loss from the respiratory system (Chapter 15, Section 3), but they also have an efficient method of excretion, that is, one that uses a minimum of water for urine production (Chapter 18, Section 4.1). Such water loss as does occur is normally made up by drinking or from water in the food, though active members of a few species from very dry habitats are able to take up water from moist air should the opportunity arise, or use water produced in metabolism.

As dormant insects are largely unable to acquire water from their surroundings, they typically have a "prevention is better than cure" strategy; that is, they use behavioral or physiological mechanisms to reduce water loss (Danks, 2000). Behavioral means include spending the dormant period in cocoons, in soil or leaf litter, under bark, and in groups (e.g., ladybird beetles). Examples of physiological strategies are reducing the size of the spiracular opening, increasing the thickness of the cuticle, especially the wax layer, altering the composition of the wax to raise the transition temperature (Chapter 11, Section 4.2), increasing the osmotic pressure of the hemolymph by synthesizing cryoprotectants, and by significantly reducing metabolic rate. Some insects, nevertheless, lose considerable body water during diapause, and in hibernating species this is often correlated with the production of cryoprotectants (Section 2.4.1) (Block, 1996). For example, yellow woolly bear caterpillars (Diacrisia virginica) enter diapause as mature larvae weighing about 600 mg. During diapause their weight falls to about 200 mg, mainly as a result of the loss of water. However, the water loss is achieved by decreasing the hemolymph volume, enabling intracellular water to be kept at a physiologically suitable level.

For estivating insects, especially those that live in areas with distinct wet and dry seasons, moisture may act as an important stimulus for continued development and activity, in much the same manner as photoperiod and temperature regulate the seasonal ecology of many temperate species (Tauber et al., 1998; Hodek, 2003). Though there is currently a lack of evidence for the importance of moisture as a seasonal regulator, Tauber et al. (1998) hypothesize that moisture may affect life cycles in three ways: (1) it may serve to induce, maintain, or terminate diapause; (2) it may be a developmental modulator, for example, by controlling rates of growth, maturation, and reproduction, as well as feeding and locomotion; and (3) It may be an important behavioral cue for such processes as molting, mating, and egg laying.

The importance of water is not restricted to postembryonic stages. During embryogenesis, also, the correct proportion of water must be present within the egg. Again, the primary problem is to prevent water loss (unlike postembryonic stages of most species, eggs cannot move in search of water or into habitats where loss is reduced!). To facilitate this a female may lay eggs in batches rather than singly, oviposit in a moist medium, and surround the eggs with protective material (Chapter 19, Section 7). In addition, the eggshell (chorion) is highly impermeable to water. As a result the egg is very resistant to desiccation and is frequently the stage in which periods of drought are overcome. Moisture may also be an important cue that triggers postdiapause embryonic development and hatching, as described in Section 3.2.3.

In view of the importance of water, it is not surprising to find that many terrestrial insects behave in a characteristic manner with respect to moisture in the surrounding air or substrate. The response may have immediate survival value for the individual concerned or may confer a long-term advantage on the individual and, ultimately, on the species. The

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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