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682 house fly, all of whose members, at emergence, leave the old habitat and disperse randomly.

After a period of maturation, they seek out new breeding sites. The category also contains species that seasonally produce populations of weakly flying, migratory individuals, for example, aphids, termites, and ants. Migrations are largely wind-dependent and may occur in every direction from the emergence site. The migration time and distance are usually short, and once individuals reach a suitable breeding site, they remain there for the rest of their lives. Indeed, on reaching such a site, some species characteristically shed their wings.

Also placed in the first category, but having migrations that are of a much grander scale, are the migratory locusts. Desert locusts, Schistocerca gregaria, for example, may travel thousands of kilometers as they move from one breeding area to another as each becomes unsuitable because of drought (Figure 22.8). Like those of aphids, etc., the migrations of desert locusts are wind-dependent. Because they inhabit fairly dry regions, breeding in the desert locust is synchronized with the arrival of a rainy season. As rain comes to different parts of the inhabited area at different times of the year, adults migrate in order to continue breeding activity. It is the winds on which locusts migrate that also bring rain to the new areas. During spring, breeding occurs in north and northwest Africa (in conjunction with rain in the Mediterranean region), in the Middle East across to Pakistan, and to the south in East Africa. In the latter regions, local seasonal rains occur at this time. As northern Africa and the Middle East become dry in early summer, locusts migrate southward on prevailing winds to an area that runs across Africa, from east to west, lying just south of the Sahara desert, then northward across southern Arabia and into Pakistan. This area is closely associated with the Inter-Tropical Convergence Zone (ITCZ), where hot, northbound air from the equatorial region meets cooler air flowing south. The mixing of these air masses within the ITCZ results in the production of rain and a reduction of wind speed so that the locusts again become earthbound. Locusts from East Africa, south of the ITCZ, move north and east on prevailing winds to be deposited in southern Arabia and India. These summer migrations may take locust swarms several hundred or even thousands of kilometers in a relatively short time. In contrast, the fall and winter movements that bring locusts to their spring breeding sites generally consist of a number of shorter migrations made over a longer period of time, mainly because the air temperatures at this time of the year are only intermittently suitable for migration. The northward migration results largely from cyclonic weather disturbances that move eastward across Africa every few days. These disturbances bring with them warm southerly winds on which locusts may be carried. As the winds push northward they mix with cooler air, which results in rainfall and temporary cessation of migration. Successive waves of warm air gradually bring the locusts to their spring habitat. The above summary of the annual movements of locusts is of necessity extremely simplified. Nevertheless, it shows how migration, based on wind currents, has evolved as an integral part of locusts' life history to facilitate year-round breeding activity through the exploitation of temporarily suitable habitats.

Finally, Category 1 includes some species (mainly Lepidoptera) whose migrations are independent of wind currents. That is, the insects do not rely on wind to make the migrations, though their movements are undoubtedly influenced by wind speed and direction. A much-studied example of a species that migrates under its own power is the great southern white butterfly, Ascia monuste (Pieridae), that migrates up and down the Florida coastline. In Florida the species breeds year-round but not in all localities simultaneously. Periodically populations comprising immature females and males of all ages make migratory flights over distances up to 150 km or more to new areas where Batis maritima (maritime salt wort),

FIGURE 22.8. Major movements of swarms of Schistocerca gregaria from spring, summer, and winter breeding areas, in relation to the position of the Inter-Tropical Convergence Zone (ITCZ). [From Z. Waloff, 1966, Antilocust Memoir 8. Crown copyright 1966. Reproduced with permission of the Controller of Her Britannic Majesty's Stationery Office.]

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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