6 



CTRCTLAR 295. U.S. DEPARTMENT OF AGRICULTURE 



data are valuable from the standpoint of control and may explain, in 

 part at least, the wide variation in the recommendations which have 

 been made for the use of oil emulsions in controlling this insect: for 

 experiments have shown that it is difficult to obtain a complete con- 

 trol of that portion settled under old scale covers, especially in en- 

 crusted infestations. Consequently, the higher the percentage of 

 specimens developing under old scale covers, or the older and heavier 

 the infestation, the heavier the concentration of oil likely to be needed 

 in the spray solution to effect a satisfactory control. 



The newly settled 

 yotmg begin almost im- 

 mediately to form their 

 covers, and by the end 

 of 6 to S hours these 

 are usually sufficiently 

 developed to conceal 

 them. The covers are 

 at first pure white, but 

 by the end of the second 

 day after their formation 

 they become light brown : 

 by the end of the first 

 week, dark brown: and 

 by the end of the second 

 week they begin to take 

 on the color of the sur- 

 face on which they rest. 

 so that by the time the 

 scales are ready for the 

 first molt the coloring of 

 the covers blends closely 

 with that of the sur- 

 roundings. 



It is evident that this 

 insect is able to incorpo- 

 rate into its cover some 

 portion of the surface 

 on which it develops, 

 for the color of its cover 

 always blends with it. 

 Figure 5 shows where 

 two specimens settled on 

 or near a black india-ink 

 line, one of which, at a. has not been touched, while the other, at 6. 

 has been removed. It is to be noted that that portion of the cover 

 of the specimen at a which is in contact with the black hue is black 

 while the remainder of the cover blends with the bark on which it 

 rests. That the hue was actually incorporated into the cover is 

 evident from an examination of the place from which the specimen 

 at b has been removed, which shows the line to be missing where it 

 was crossed by the removed cover and to be intact beyond what was 

 the outer margin of the cover. This would seem to indicate quite 

 clearly that the insect is able to utilize the surface of the bark on 



Figuke 5.— Two immature individuals of the obscure scale which 

 settled on or near a line made with black india ink: o. Specimen 

 left in place showing a portion of it in contact with the black 

 line; b, specimen removed showing the portion of the line gone 

 where it was formerly covered by the scale cover. X 20. 



