BUREAU OF ENTOMOLOGY. 509 



principal injury consists in large mines in the wood near the line 

 of contact with the ground, necessitating the frequent resetting and 

 even replacement of the damaged poles. The character and habits 

 of these insects have been studied during the year, and one of them 

 has been shown to have damaged seriously from 10 to 15 per cent of 

 the chestnut poles which have been set in the ground for from 10 to 

 12 years in lines in North Carolina, Virginia, West Virginia, Mary- 

 land, and the District of Columbia. The same insect has also seri- 

 ously damaged a considerable proportion of the arborvitse telephone 

 poles in part of a line in Illinois. It has been found that by impreg- 

 nating the poles with creosote, either by the open-tank process or by 

 the cylinder-pressure process, the poles can be eU'ectively protected. 

 The same line of investigation has been extended from the telegraph 

 and telephone poles to mine props and crossties. 



INVESTIGATIONS OF INSECTS DAMAGING DECmUOUS FRUIT TREES. 



The investigations of insects damaging deciduous fruit trees have 

 been carried on as before under the direct supervision of Mr. A. L. 

 Quaintance. Several of last year's projects have been continued, 

 and with the spring of 1907 certain additional investigations were 

 entered upon. 



THE PEAK THRIPS. 



Further details in the life and habits of the pear thrips, a serious 

 enemy of deciduous fruit in California, have been investigated, espe- 

 cial attention having been given to determining the variations in time 

 of appearance of the adults on the trees in the spring due to climatic 

 conditions. Weather conditions obtaining during the spring of 1911 

 considerably modified the behavior of the insects, and they emerged 

 from the ground over a considerably longer period than usual and 

 were much less abundant at a given time than during former years. 

 For this reason spraying operations against the adults were not as 

 effectual as heretofore, and spraying against the larvae, later appear- 

 ing, was of correspondingly greater importance. 



The spraying experiments under way in orchards during 1910 

 were quite successful, as shown by the condition of crops on sprayed 

 and unsprayed plats at picking time of the fruit in the fall. Thus, 

 in the case of prunes in the Santa Clara Valley, the yield from a 

 sprayed block was 367.93 boxes per acre, with a value of $320.82, as 

 compared with a yield of 7 boxes per acre on the unsprayed block, 

 with a value of $6.65. On a block of trees thoroughly plowed and 

 cross-plowed in the fall for the destruction of pup?e in the ground 

 the yield was 85.65 boxes per acre, with a value of $74.85. 



In another orchard the yield from 300 trees, which had been 

 thoroughly plowed the fall previously and given three spray applica- 

 tions in the spring, was 136.08 boxes per acre, with a value 

 of $190.08, while on an adjacent block of 98 trees, which received 

 thorough cultivation in the fall, but no spray applications in the 

 spring, the yield per acre was 26.46 boxes per acre, with a value of 

 $34.02. From the check block, which received no cultivation or 

 spraying, the yield was but 2 boxes of fruit per acre, with a value 

 of $2.59. 



