21 



tively much shorter than in P. iunitmcrabilis. About the time when 

 the migration to the twigs began, late in October, the great majority 

 of the larvae were found on the underside of leaves, mostly along the 

 ribs. A large number were also found on adjoining twigs, generally in 

 and around the forks, in excresences, or near buds or other projections. 

 At this time they run about quite actively in search of suitable places 

 for hibernation. At this time is noticeable the delicate layer of waxy 

 secretion which gives the insect a somewhat grayish appearance. This 

 secretion is more or less distinctly broken up so as to form a series of 

 waxy plates. 



On November 1, 1898, practically all of the larvae had settled for 

 hibernation. Upon one branch about 18 inches long 150 larvae were 

 counted. They were most numerous on twigs and branches from one- 

 eighth to one-fourth of an inch in diameter. None had appreciably 

 increased in size, but their color was considerably darker and more 



Fig. 17. — Pulvinaria acericola : a, full-grown female, from above, on leaf, with 24 hours' secretion of 

 egg sac; b, same, with egg sac completed, from side; c, same, from above — enlarged (original). 



dingy looking, harmonizing quite well with the coloration of the bark. 

 This change in color seems to be due to the waxy secretion, which 

 serves as a winter covering and also as a means of concealment. So 

 close does this resemblance in color to the bark become that to the 

 naked eye a twig thickly covered with the insects seems simply blis- 

 tered or pustulate. 



In December the conditions had changed but slightly. The larvae 

 were of a dingy, yellowish gray color, more or less spotted with purple, 

 except the mediodorsal ridge, which was entirely yellowish. The whole 

 surface was rather rough and covered each side with three more or less 

 distinct rows of round or squarish scales of waxy secretion, looking 

 like tortoise shell. On March 31 there had been practically no change. 



By the 8th of April, on potted trees, were found both males and 

 females. The largest females were about 3 m,n in length by 1.8 mm in 

 diameter. They were dark purple in coloration, with the median 

 15.118 2 



