Postembryonic Development

produced when the population density remains continuously low for a long period of time, 649

and the gregarious phase, typical of high-density populations. It is not feasible here to describe in detail the many differences that occur between the two phases. Suffice it to say there are significant differences in their structure, color, physiology (growth rates, occurrence of diapause, reproductive capacity), and behavior (feeding activity, migratory habits), which enable populations to develop and reproduce at the optimum rate according to the habitat in which they occur. For example, female solitary locusts, for which food is abundant, are larger, may lay up to five times more eggs, and have slightly shorter wings than gregarious females. Because of the greater population density, gregarious females must have the capacity to migrate to new food supplies (see also Chapter 22, Section 5.2) for which smaller body size and larger wings will be advantageous. In addition, they accumulate more fat (used as an energy source during migration) than solitary females, an aspect that may be correlated with production of fewer eggs (Pener, 1991; Pener and Yerushalmi, 1998).

Some experimental evidence suggests that the influence of population density and other environmental factors on phase determination is exerted via hormones, especially JH. For example, adults with some features of solitary locusts can be produced by implanting corpora allata or by applying JH to gregarious larvae. Solitary adults are structurally more juvenile than gregarious adults, and, as noted above, solitary females lay more eggs than their gregarious counterparts, both of which features are related to greater levels of JH in the hemolymph. Because of the above-normal levels of hemolymph JH, the molt glands of solitary individuals do not degenerate at eclosion. However, they do not produce ecdysone so never trigger a further molt. In the general model for hormonal control of polyphenism proposed by Nijhout and Wheeler (1982) and Nijhout (1994) phase change would occur as a result of the JH levels during specific critical periods of a stadium. However, other authors, notably Pener (1991), Pener and Yerushalmi (1998), and Breuer et al. (2003), while accepting that JH can induce certain characteristics of the solitary phase, have argued that JH is not the primary causal factor in phase determination; that is, changing JH levels are simply a result of other, as yet unknown, factors that induce phase change.

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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