BUREAU OF ENTOMOLOGY. 631 



reveal any points of practical value. It was found that the Roentgen 

 rays have apparently no effect whatever on the sexual organs of the 

 insects. 



At the Dallas laboratory much work was done to determine the 

 relative toxicity of a large numlx^r of poisons on different species of 

 insects. In this work the killing dose, the physiological effects on 

 the insects, and the effects on the soil were considered. 



In cooperation Avith the South Carolina experiment station work 

 in the practical control of the cotton root-aphis and cotton wireworm 

 was conducted at Marion, in that State. Some of the results have 

 been published by the South Carolina station. 



During the season there was an unexpected outbreak of the cotton 

 caterpillar throughout the Southern States. This insect was for- 

 merly the most dreaded enemy of cotton in the United States, but 

 for about a quarter of a century has not attracted much attention. 

 During the year, hoAvever, there occurred an outbreak practically as 

 extensive as any that had been recorded. Observations on this phe- 

 nomenon were made and through publications and letters advice was 

 given the planters regarding the control measures to be practiced. 



INVESTIGATIONS OF INSECTS DAMAGING FORESTS. 



The work of the bureau on insects affecting forest trees and crude 

 and finished forest products has been carried on during the year 

 under the direct supervision of Dr. A. D. Hopkins, as in previous 

 years, and the same general lines have been followed. There has 

 been a continued eft'ort to demonstrate the practicability of prevent- 

 ing a large percentage of the waste of forest resources heretofore 

 caused by insects, and there has, in consequence, been a greatly in- 

 creased interest in the subject on the part of small and large private 

 owners of timberlands as well as by State and Federal officials who 

 are charged with the management of public forests. There has been 

 a more general adoption of insect-control policies in connection with 

 other advanced methods of forast protection, and also a more general 

 confidence in expert advice on matters relating to the control of 

 injurious insects. 



The principal injuries of the year have been, as before, by the 

 Dendroctonus beetles on the pine, spruce, and fir of the Northwest 

 and Pacific Coast States, and on the pine of the South Atlantic and 

 Gulf States. In sections where no attempt has been made by private 

 owners or public officials in charge to control the depredations a 

 great waste of forest resources has continued, but in certain sections 

 where proper efforts have been made in the way of control the waste 

 has been reduced or entirely stopped. The hickory barkbeetle has 

 caused the death of a large number of young and old trees in the 

 North Atlantic and Groat Lakes States, but information given out 

 from the bureau has resulted in a large amount of successful control 

 work carried on by the owners of woodlots and by superintendents of 

 municipal and private parks. 



The ravages of the so-callod chestnut bark disease attracted a great 

 deal of attention during the year, and recent investigations have indi- 

 cated that certain insects with bark-boring liabits are intimately asso- 

 ciated with this disease and with other diseases affecting the chestnut. 

 In fact, the evidence seems almost conclusive that the infection of the 



