EXAMINATIONS OF THE SCALE INSECTS. 15 



EXAMINATIONS OF THE SCALE INSECTS. 



After fumigation, the fruit was kept in an outbuilding on the 

 Agricultural Department grounds, the temperature varying mostly 

 between 30° and 40° F., being rarely higher than 45° F. In 1906-7 

 the fumigated fruit for examination as to condition of scales was 

 taken direct from this storehouse; but in 1907-8 it was first held for 

 a couple of days in a warm room, which induced a prompt discolora- 

 tion of the dead scales, greatly facilitating their recognition. The 

 plan was to make two examinations of the scales on each lot of fruit 

 fumigated: The first two weeks, and the second four weeks, after the 

 time of fumigation, and this in the main was adhered to. All ex- 

 aminations of scales were made by aid of a dissecting microscope, and 

 a dissecting needle was used to remove the scale proper, exposing the 

 body of the insect. The color of the body was relied upon to de- 

 termine if the insect were dead or alive, and there was not often 

 difficulty in thus definitely classifying them. In some cases, ex- 

 amination of doubtful specimens was made under a compound 

 microscope to detect possible body movements, and a method of 

 staining was used to a limited extent. In all cases, specimens doubt- 

 fully dead were regarded as alive, and, as will be noted in the tabu- 

 lated results for 1906-7, these doubtful cases were numerous. 



In 1907-8, however, the expedient of warming the fruit for a 

 couple of days before each examination always resulted in the prompt 

 discoloration of the scales, leaving no doubt as to their condition. In 

 view of the uniformly successful results in killing the scales in all 

 experiments made in 1907-8, and many of them duplicates of those 

 made in 1906-7, it is considered practically certain that the insects 

 regarded as alive in 1906-7 were in reality dead, but not showing 

 sufficient discoloration for positive recognition on account of the 

 comparatively low temperature at which they were held. 



The supply of infested fruit for fumigation was kept in the original 

 barrels in a local cold-storage plant, being taken out shortly before 

 needed, the time depending upon the nature of the test to be made. 

 Thus in treatment of fruit in a dry condition it was necessary to 

 remove it several days in advance, so that the moisture condensing 

 on the cold fruit would dry. In the fumigation of fruit in a moist con- 

 dition, however, the condensed moisture on the cold fruit immediately 

 after coming from cold storage put this in the desired condition for 

 experiment. 



An important question in the employment of hydrocyanic-acid 

 gas in the destruction of scale insects on apples was the possibility of 

 injury to the fruit. In this matter the Bureau of Entomology had 

 the expert aid of Mr. William A. Taylor, pomologist, of the Bureau of 

 Plant Industry, and his associates, who are also responsible for the 

 correctness of names of varieties. There is also the question of 

 89165— Bull. 84—09 3 



