BUREAU OF ENTOMOLOGY. 241 



had entered the wood, resulted in the killing of 80 to 90 per cent 

 of the larvse. This indicates quite conclusively that a comparatively 

 inexpensive treatment during the early stage of the growth of the 

 trees will serve to protect the plantations from serious damage. 



The percentage principle of controlling Dendroctonus beetles has 

 stood the test of another year and appears to be one of the most 

 important practical results of the investigations of this branch. The 

 timber of the areas in which it has been applied during the past ten 

 years has continued in a healthy condition. 



Continued investigations by Dr. Hopkins of the relation of lati- 

 tude, longitude, and altitude to the periodical activities of insects 

 and their host plants have resulted in rapid progress toward the 

 development of a bioclimatic law which, it is claimed, will have a 

 broad application not only to entomological research and practice 

 but to general biological research and all periodical practice in 

 agriculture. 



INVESTIGATIONS OF INSECTS INJURIOUS TO VEGETABLE AND 



TRUCK CROPS. 



The work on insects injurious to vegetable and truck crops has 

 been conducted, as heretofore, under the direction of Dr. F. H. Chit- 

 tenden. The most important subjects of research during the year 

 have been insects as carriers of plant diseases; insects injurious to 

 potatoes, sugar beets, beans, and peas; and insects injurious to 

 cucurbits and cruciferous crops. 



IxSECTS AS CARRIERS OF PLANT DISEASES. TllC WOl'k OU lUSectS aS 



disseminators of plant diseases was begun in May, 1916, particular 

 attention being given to the carriers of cucumber diseases, and was 

 conducted in cooperation with the Bureau of Plant Industry and 

 owners of salting stations at Plymouth, Ind., Madison, Wis., and 

 Big Eapids, Mich., the work being continued throughout the grow- 

 ing season. Demonstration and experimental spraying and trap- 

 crop work were undertaken and community demonstration spraying 

 Avas conducted over a considerable acreage at each station. Many 

 experimental spray plots w^ere utilized and a large variety of insecti- 

 cides were tested. 



Experimental work to determine the relation of the striped cucum- 

 ber beetle and the 12-spotted cucumber beetle to bacterial wilt and 

 the mosaic disease of cucumbers and the status of these beetles as 

 factors to be dealt with in the control of these diseases is still in 

 progress. Several important points have been brought out, result- 

 ing in the elimination of a number of insecticides as ineffective or 

 injurious to the plant. The most promising have been retained for 

 further tests during the coming season. It was noted that Bordeaux 

 mixture acted strongly as a repellent and consequently was unsuit- 

 able for use where poisoning of the beetles was desired. On trap 

 crops 98 per cent of the beetles were destroyed with the crude oil 

 soon after their emergence. Additional work will have to be done 

 to determine the value of the various trap crops. Fall treatment of 

 cucumber fields proved of great value in destroying the beetles before 

 hibernation. Observations of vital importance from both the scien- 



33382°— AGR 1917 16 



