684 the primary host plant, is abundant. In contrast to the situation in locust migration, it is not the arrival of adverse conditions that stimulates migration in A. monuste. The migrations occur from areas where food and oviposition sites are still abundant. Though the sun has been suggested as a reference point by which the butterflies orient themselves during flight, local cues are also important. For example, the insects may closely follow the shoreline, roads, railway tracks, or telephone lines.

In his second category Johnson (1969) included species whose migration is in two parts, an emigration to feeding sites where sexual maturation occurs, followed by a return flight to the original (or a similar) site of emergence where the insects oviposit. Many Odonata, for example, do not remain in the area of the pond from which they emerge but migrate to nearby woods or hedgerows to prey on other insects until mature. They then return to water, mate, and lay eggs. Some species regularly return to the feeding habitat between each oviposition period. Some species of mosquitoes also have a two-part migration, first to find a host on which to feed and later to locate an egg-laying site. In some cases the initial part of the migration is considerably longer than the second. Like that of Odonata, the migratory flight of some mosquitoes is wind-independent. For most migratory species, however, wind determines the direction and distance traveled.

The third category includes species that again have a two-part migration. The initial migratory flight takes the species to suitable hibernating or estivating sites where they enter diapause, after which they return to the region in which they emerged and reproduce. Within this type of migration three subcategories can be recognized. In the first, the sites of diapause are within the general breeding area of the species. Species that adopt this arrangement include the Colorado potato beetle, Leptinotarsa decemlineata, and the corn thrips, Limothrips cerealium.

Belonging to the second subcategory are species that migrate to a climatically different region prior to diapause. Especially common is migration between warmer lowland areas where the insects have emerged and mountainous regions, either to avoid summer heat or to overwinter. Such migrations are seen in various noctuid moths, for example, the army cutworm, Euxoa auxiliaris, in Montana, which moves southwest to the Rocky Mountains, and in some coccinellid beetles, such as the convergent lady beetle Hippodamia convergens, in northern California. Adult beetles first appear in early May and soon most migrate, using prevailing winds, to mountain canyons in the Sierra Nevada range where they aggregate under stones, litter, etc., and enter diapause. Diapause lasts for about 9 months, and the following February and March adults, again windborne, return to the valleys where a new generation is produced. Breeding activity is thus closely correlated with mass emergence of spring-breeding aphids. (Interestingly, as a result ofhuman agricultural activities, aphids are now available on a year-round basis, and some populations of H. convergens no longer migrate but through the summer produce several generations of progeny, the last one of which overwinters in diapause at the breeding site.)

Migrations included in the third subcategory differ from those of the second subcategory only in terms of the distance covered, especially during prediapause movements. The classic example of a species in this group is the monarch butterfly, Danaus plexippus, whose remarkable migration (Figure 22.9) is intimately associated with the abundant Asclepias (milkweeds) found in North America. Two major populations of monarchs exist. The smaller western population (thought to have evolved from that east of the Rockies) spends the summer in the valleys and coastal areas of British Columbia, Oregon, Washington, Nevada, and California, and migrates each fall to at least 38 permanent overwintering sites along the Californian coast. The eastern population, whose summer range extends from the Great

FIGURE 22.9. Spring and fall migrations of the monarch butterfly in North America. [From L. P. Brower and S. B. Malcolm, 1991, Animal migrations: Endangered phenomena, Am. Zool. 31:265-276. By permission of the American Society of Zoologists.]

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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