36 THE MONTHLY BULLETIN. ' 



The fruit may be scabbed and curled or otherwise deformed by the 

 constant chafing. 



Life History.— As stated above, the eggs are inserted in the stem, 

 leaf or small fruits of the host. They hatch in from four to five days, 

 the larvffi or "white thrips" beginning to feed at once and to do damage. 

 When full grown, which takes from two to three weeks, they drop to 

 the ground and after penetrating several inches enclose themselves in a 

 small cell, where they remain throughout the transforming or pupal 

 period. This period usually begins about September and continues 

 throughout the months of October, November and December, when adult 

 insects are formed. These remain in the ground until February before 

 emerging. The transformation from the larval to the adult stage 

 occupies several months, the slow growth being probably due to the 

 cold winter season. 



Distribution.— The pear thrips is distributed throughout the Sacra- 

 mento and San Joaquin valleys, and particularly in the following 

 counties: Santa Clara, Alameda, Contra Costa, San Joaquin, Solano, 

 Sacramento. Yolo, Napa and Sonoma. It has also been reported from 

 the Sierra foothills in Placer County. 



Food Plants. — This insect is particularly a deciduous tree pest and 

 works great damage upon the leaf and flower buds as well as the 

 young fruit. The initial damage is done just before or after blossom- 

 ing time. The pear suffers probably more than any other tree due to 

 ravages of this insect, although prunes and plums are also severely 

 attacked. Peaches, apricots and almonds also receive serious damage 

 some seasons. The following are other hosts of this pest :• apple, 

 cherry, fig, grape and English walnut. 



Control. — ^Government Formula. — "The formula which has given 

 the best results is made up of the 3 per cent distillate oil emulsion, to 

 which is added from 1 per cent to If per cent of tobacco extract No. 1 

 (black leaf containing 2.75 per cent nicotine) or tobacco extract No. 2 

 (sulphate of nicotine or black leaf 40), which is 40 per cent nicotine, 

 at the rate of one part to from 1,500 to 2,000 parts of the spray mixture. 

 The distillate oil emulsion may be obtained from several dealers in 

 chemical and spraying supplies, or may be made at home. By the use 

 of the homemade emulsion, a considerable proportion of the cost of 

 spraying is saved and, what is more important, the quality of the emul- 

 sion is above reproach, when good materials are properly used in its 

 manufacture. ' ' 



Whitewash. — Mr. Earl Morris, horticultural commissioner of Santa 

 Clara County, has had remarkable results in controlling pear thrips on 

 pear trees by the use of a whitewash spray. His work covers a period 

 of two years. The trees were sprayed with thick whitewash when the 

 buds were just beginning to open. Some of his results as published in 

 Bull. No. 238, Cal. Agrcl. Exp. Sta-. are as follows: 



"We used eighty (80) pounds of quicklime for one hundred (100) 



*From G. E. Merrill, M. B. Cal. Hort. Com., Vol. I, No. 2, p. 54. 



