Ihv

686 Plains to the eastern seaboard, migrates on prevailing winds southward and westward during

September to November to some 10 permanent overwintering sites in the Transvolcanic Range of central Mexico. At these cool and moist sites, which are dominated by stands of the oyamel fir (Abies religiosa), extremely dense and spectacular clusters of monarchs are able to spend the winter until the milkweed flora of the north reappears the following spring. Through the winter the monarchs remain in reproductive diapause, but about the end of February egg development and mating begin and the butterflies initiate a relatively rapid remigration northward (again using prevailing winds), reaching the southern United States in late March and early April.

For many years there was debate over whether the overwintered monarchs were responsible for establishing the spring generation over the entire range of the eastern population (the "single sweep hypothesis") or whether the overwintered butterflies produced offspring only in the southern United States and then died, the offspring continuing the northward movement (the "successive brood hypothesis") (Brower and Malcolm, 1991). This controversy was resolved in favor of the successive brood hypothesis by analyzing the cardenolides found in the body of the butterflies. The cardenolides, which are sequestered by the monarch larvae as they feed on the milkweeds and serve to deter would-be vertebrate predators, are characteristic for each Asclepias species and can thus be used to determine where the butterflies lived as larvae. Essentially, the study showed that overwintered, early spring migrants to the southern United States had cardenolides characteristic of A. syriaca, a northern species, which they would have acquired as larvae the previous summer. However, the monarchs that reached North Dakota east to Massachusetts in May and June had cardenolide patterns typical of Asclepias species found only in the southern United States (Malcolm et al., 1991). Through the summer period, there may be several non-migratory generations of monarchs, only the last generation of adults entering reproductive diapause and developing migratory behavior. Tragically, the overwintering sites of both eastern and western populations of the monarch are under severe pressure as a result of numerous and varied human activities. Especially significant is illegal deforestation in the Mexican national parks where the eastern population's overwintering sites are located (Brower et al., 2002). Logging not only reduces the monarch's habitat, but by fragmenting the forest it also opens the area to localized climate changes, especially freezing temperatures, which increase the butterfly's mortality. Brower and Malcolm (1991) (p. 270) concluded that the monarch's "eastern North American migratory phenomenon is now threatened with extinction and will probably be destroyed within 10-20 years."*

As the above examples demonstrate, migration can take many forms yet its common purpose is to improve a species' ability to survive and multiply. For most species, wind supplies the power for migration, and their physiology and behavior have so evolved as to make best use of this.

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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