THE PEAR THRIPS AND ITS CONTROL. 57 



MIGRATION OF ADULTS. 



The migration of adult thrips is as yet only imperfectly understood. 

 They have wings and are free to fly if they choose, but weather condi- 

 tions and food supply influence very decidedly their inclination to move 

 about. The tendency is for the thrips to remain quite closely with 

 the trees wherever there are only a few individuals and where the 

 supply of food is abundant. They then fly up during the warm, 

 quiet parts of the day, but do not travel far. It often happens that 

 the insects are so numerous as to kill the early buds or to so injure 

 them that these become brown and dried and do not offer suitable 

 food; the thrips then migrate to other less affected orchards. This 

 migration often occurs before the period of oviposition begins, in 

 which case no new brood is started to infest such an orchard during 

 the following year. This explains why thrips may injure an orchard 

 during one season and seem to have almost entirely disappeared from 

 it the next. This occurrence has led some orchard- 

 ists to believe that eventually the thrips may move 

 away permanently or die out. This supposition is 

 not correct, and it will be only a matter of a year 

 or two until these orchards will again be attacked. 



Migration, then, occurs only during warm, clear 

 weather and is hastened by a desire for better 

 food or for suitable conditions for ovipositing. * Eggs. Highly magni- 

 Thrips locally do not travel in any particular fie(L (Author's mustra. 

 direction, such as south, or east, or west, but 

 distribute themselves generally wherever conditions are favorable for 

 their propagation. 



OVIPOSITION. 



During the season of 1909 oviposition was not observed until 

 March 10, and by March 15 any number of individuals could be seen 

 placing their eggs. A few larvas, however, were collected from almond 

 trees on February 26, indicating that earlier eggs had been placed. 

 The period of maximum oviposition begins about March 15, and 

 almost all individuals will be found placing eggs after this date for 

 a period of about four weeks. Ovipositing continues early and late 

 during the day and in all conditions of weather. 



THE EGG. 



The egg (fig. 14), a white, bean-shaped body, is always embedded 

 in the tender tissue of the stem, leaf, or in small fruits, and is thus 

 protected. After about four days the larva hatches and pushes out 

 through the incision immediately above it. 



