64 



newly set young upon it, and crawling young were seen just before 

 it was peeled and eaten. 



December 11, 1907, two infested Ben Davis apples were taken 

 from a package which had been in cold storage, and were placed in 

 a warm room. Crawling young appeared on them after ten or twelve 

 days, and some of these set and began to develop. One of these apples 

 was kept two weeks and the other twenty-six days, and on the twenty- 

 fifth day three crawling young were seen. 



The Life History of the San Jose Scale in Illinois 



The only detailed experimental studies of the life history of the 

 San Jose scale hitherto published are those of Theodore A. Pergande, 

 in Howard and Marlatt's comprehensive discussion of this insect, 

 which appeared in 1896.* According to this report, four complete 

 generations of the San Jose scale were regularly bred at Washing- 

 ton, with the possibility of a partial fifth generation, and the astound- 

 ing total of 3,216,080,400 was given as the possible number of de- 

 scendants from a single female in a single season. 



Noticing that in these breeding experiments no account was taken 

 of the difference in the number of annual generations, and conse- 

 quently in the number of descendants produced by the first-born of 

 the first-born of each generation, and by the last-born of the last- 

 born of the same series — a consideration to which attention was 

 called by the writer in 1906 f — it was thought best to duplicate these 

 studies at Urbana by methods which would bring this factor into 

 view ; and the problem was assigned to Mr. West for solution in 1908. 



Young and vigorous trees of the Ben Davis variety, on which 

 the insect multiplies freely, were selected for the purpose ; and glass 

 rings 10 mm. in height and 35 mm. in interior diameter were fixed 

 on the tree by means of paraffin or wax. Into one of these cylinders 

 were put crawling young which were to start a new generation. The 

 ring was covered either with a band of closely woven muslin or with 

 glass. Cylinders with glass covers were not satisfactory, however, if 

 so placed as to receive the direct rays of the summer sun, and the 

 cells were almost invariably placed on a shaded part of the tree. It 

 was our plan to rear two series of generations, starting in each case 

 with the firsc and the last young of each brood of the insects. By 

 taking the first-born of each brood, the generations were brought as 

 close together as possible, giving the maximum number for the sea- 

 son. By taking the last-born of each brood, the generations were 

 separated as widely as possible, giving the minimum number for a 

 season. 



*Bull. 3, N. S., Div. Ent., TJ. S. Dept. Agr., p. 43. 



tThe Corn Root-aphis and its Attendant Ant. Bull. 60, Bur. Ent., U. S. 

 Dept. Agr., 1906, p. 31. 



