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 pupa? 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 

 Hecllands. 



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. 



DESCKIPTION OF PKOCESS. 



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 



