. Bulletin of the Department of Agriculture. Agriculture; Agriculture. THE TEREAPIN SCALE. 19 LEAFWARD MIGRATION. The migration to the leaves begins immediately after emergence. The larvae start emerging usually about 10 a. m., or even earlier if the temperature is high, and by 3 p. m. the daily migration has nearly ceased. At Mont Alto, Pa., during the noon hours of June 15 to 20, the branches of infested trees were swarming with countless numbers of migrating larvge. During the leafward migration the larvae are strongly phototropic and negatively geotropic. The time required for an indi
. Bulletin of the Department of Agriculture. Agriculture; Agriculture. THE TEREAPIN SCALE. 19 LEAFWARD MIGRATION. The migration to the leaves begins immediately after emergence. The larvae start emerging usually about 10 a. m., or even earlier if the temperature is high, and by 3 p. m. the daily migration has nearly ceased. At Mont Alto, Pa., during the noon hours of June 15 to 20, the branches of infested trees were swarming with countless numbers of migrating larvge. During the leafward migration the larvae are strongly phototropic and negatively geotropic. The time required for an individual to make this mi- gration and to take its position upon the leaf is remarkably short. Two hours is about the average time from emergence to the completion of the migra- tion. Many reach the leaves and attach in less than an hour, but others, especially those that have ascended dead branches, may con- tinue to move about for several days if a suitable leaf is not found sooner. It is very unusual for the larvae to relocate when they have once taken position upon a leaf, though they do this when the leaf loses its vigor. The larvae, except in rare and unusual cases, attach to the underside of the leaves, mostly alongside and parallel to the midrib, or the larger veins. (Fig. 5.) Larvae usually attach to the first avail- able leaves. The basal leaves upon an infested branch are always more heavily infested than those farther up. A sticky secretion upon the very young leaves repels the young larvae and prevents them from attaching. The wooly coat of the fruit pro- tects it from larvae. Larvae frequently crowd upon the fruit, but in their struggles to free themselves from the fuzz they invariably fall to the ground. The rate of migration varies with the temperature and the surface upon which the larvae are placed. Table XIII gives the rate per hour, time, temperature, and the distance traveled by five migrating larvae of the first instar upon smoked wrapping paper. The average
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