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 a 
not correct, and it will be only a matter of a year 
or two until these orchards will again be attacked. 4 
Migration, then, occurs only during warm, clear 
weather and is hastened by a desire for better 
: atte : Ape Fig. 14.—The pear thrips: 
food or for suitable conditions for ovipositing. Eggs. Highly magni- 
Thrips locally do not travel in any particular ed. (Author's illustra: 
. : tion.) 
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 larve, 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. 
