THE CITRUS THRIPS. 19 
number of generations is greater in exceptionally long hot summers 
than in more moderate ones. 
Cool, cloudy, or rainy weather, on the other hand, at once markedly 
diminishes the various activities of the insects. They then seek 
shelter in groups in the pits or curls and on the underside of the 
leaves, about the stem ends of the fruit, and in the crotches and 
angles of the stems. Growth, molting, and emergence are retarded. 
With temperatures ranging between 40° and 50° F., in November and 
December, larvae and pupae often live fully a month without change, 
scarcely feeding at all, and as the weather continues to grow colder 
both they and the adults die off, leaving only unhatched eggs to 
produce the succeeding spring generation. 
PECULIARITIES OF INFESTATION DUE TO FEEDING HABITS OF THE ADULT THEIPS. 
Feeding only upon the newer tissues, the adult citrus thrips are 
active in selecting young and healthy trees and often suddenly mi- 
grate from one set of trees to another or from one orchard to another. 
In localities where, owing to favorable cultural conditions and large 
plantings of young trees, an abundance of new shoots occurs in a 
close succession of growths, adults will congregate in immense num- 
bers and remain throughout the season. The resultant damage in 
such localities is often entirely out of proportion to that occurring 
in other parts of the same district. The explanation of excess in- 
festations in certain orchards and in certain localities is simply food 
preference. Areas of this sort occur typically along the foothill 
slopes, both in the San Joaquin Valley and near Eiverside and 
Eedlands. 
In older orchards, where some of the trees have been cut back and 
rebudded, thrips will congregate on the watershoots and buds from 
every part of the orchard and in such numbers as greatly to retard 
the growth of the buds. The damage done in old orchards sur- 
rounded by young trees is often very slight for the reason that the 
thrips confine themselves almost exclusively to the latter. In sea- 
sons like 1911, when the climatic conditions are such as to minimize 
growth, the insects are compelled to feed to a greater extent upon the 
fruit with consequent greater damage. 
OVIPOSITION. 
DESCRIPTION OF PROCESS. 
The following is a description of oviposition under natural con- 
ditions as observed in a single specimen at night during cool weather, 
the observations being made with the aid of an electric pocket lamp 
and a hand lens. Attention was first attracted to the specimen by 
its indifference to the light. For a half hour it remained in a space 
