The Abiotic Environment

As poikilotherms, insects have a metabolic rate that within species- and stage-specific 687

limits is proportional to temperature. Their rate of development within these limits is inversely proportional to temperature. Outside these limits insects will survive, but their development is retarded or prevented. The temperature extremes for survival are known as the upper and lower lethal limits. Survival at extreme ambient temperatures may be accomplished by (1) behavioral means, such as burrowing or ovipositing in a substrate, and/or (2) entering a physiologically dormant condition (diapause). At below-freezing temperatures insects may also become freezing-tolerant, that is, capable of withstanding freezing of their extracellular fluids, or, when they are freezing-susceptible, become supercooled. In both arrangements, polyhydroxyl cryoprotectants, thermal-hysteresis proteins, and (for freezing-tolerant species) ice-nucleating proteins are important. In species from habitats whose climate is suitable for development and/or reproduction for a limited period each year, temperature may be an important synchronizer of development and/or eclosion.

Photoperiod, the naturally occurring 24-hour cycle of light and darkness, exerts both short-term and long-term effects on behavior and physiology, which keep insects in tune with changing environmental conditions. In a few species changing light intensity triggers daily activities; that is, they arise exogenously. However, in most species, diurnal (circadian) rhythms of activity, for example, locomotor activity, feeding, mating behavior, oviposition, and eclosion, originate endogenously and are phase set by photoperiod.

By responding to seasonal changes in photoperiod insects can exploit suitable environmental conditions for development and reproduction and survive periods when climatic conditions are adverse. Among the long-term processes affected by photoperiod are the nature and rate of development, reproductive ability and capacity, synchronized eclosion, diapause, and possibly cold-hardiness.

Diapause is a genetically determined state of suppressed development. It may occur at any stage of the life history, though this is usually species-specific. Photoperiod exerts its influence at a stage earlier than the one in which diapause occurs, thus ensuring safety against prematurely unseasonal weather. Induction of diapause is, in almost all species, a response to the absolute day length (number of hours of light in a 24-hour cycle) rather than daily differences in the day length. For a species, there is a critical day length at which the incidence of diapause (proportion of individuals that enter diapause) changes markedly. Long-day insects develop continuously at all day lengths above the critical day length (usually about 16 hours of light per day) but enter diapause at shorter day lengths. In short-day insects, development is continuous at day lengths below the critical value (usually about 12 hours). In short-day-long-day insects, development is continuous at short and long day lengths, but at intermediate day lengths (about 14-16 hours of light per day) the incidence of diapause is high. Long-day-short-day insects develop continuously within a narrow range of day lengths (16-20 hours of light per day) and enter diapause at all other day lengths. The value of the critical day length for a species may change with temperature, latitude, and food availability.

Water is an important determinant of the distribution and abundance of insects. A problem for most terrestrial species is to reduce water loss from the integument and tracheal system and in excretion. In postembryonic stages this is achieved by means of a relatively impermeable cuticle, valves and/or hairs that reduce water vapor movement out of the tracheae, production of highly concentrated urine, as well as by selection of more humid microclimates. Eggs are covered with a cuticle-like chorion and may be laid in an ootheca and/or substrate. For some species in cold climates snow cover may be important as an insulator and in preventing desiccation.

688 In addition to temperature and light, important abiotic factors affecting the distribution and abundance of aquatic insects are oxygen content, ionic content, and rate of movement

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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