68 



.ber 28 is equivalent to 8,803,283 adult scales — a number sufficient 

 to cover 94.8 square feet. 



Even this estimate of a possible product of multiplication must 

 be regarded as excessive if we take note of the fact, reported by 

 Lowe and Parrott, of New York,* that an average of nearly 40 per- 

 cent of the young scales may perish, apparently from mere physi- 

 ological causes, without settling down to feed and secrete the pro- 

 tecting scale. In Mr. West's studies no attempt was made to trace 

 the fate of any of the young except those chosen as parents of the 

 generation to follow. 



These data of the Urbana experiment, obtained from a repro- 

 duction season beginning May 30 and closing October 28, no doubt 

 give us, however, a product very much smaller than might be worked 

 out for southern Illinois, and probably a larger product than the 

 northern Illinois normal rate of increase. More than 75 percent of 

 the entire theoretical product of the season was but two weeks old 

 or less October 28, and 8 percent of the scale insects alive at that 

 date would have been but one day old. A relatively slight lengthen- 

 ing of the period of reproduction would evidently have added enor- 

 mously to the total number produced, t At Alton, crawling young 

 were seen, in 1908, up to November 9, and in 1906 newly born young 

 were found by R. D. Glasgow, in Williamson county, January 4. It 

 is certain that young fruit-trees are much more rapidly destroyed 

 in southern Illinois by San Jose scale than in the northern part of 

 the state, and that the scale spreads more rapidly there and is more 

 difficult to keep in check; and our experience also shows that in- 

 festation by this insect is decidedly more injurious to susceptible 

 plants in southern Illinois than it is in the central part of the state. 



Tests of Orchard Sprays 



Comparative tests of orchard sprays for the San Jose scale have 

 been many times made, with the general result that the modern lime- 

 sulphur preparations have come into very general use ; and they 

 seem, likely to maintain this lead particularly by reason of a special 

 value as fungicides which gives them an advantage over the petroleum 

 preparations, their only real competitors. Nevertheless, careful ex- 

 periments made by the office force of the State Entomologist from 

 1907 to 1911 seem still worthy of report, at least as a part of the 

 permanent record. 



It was the principal purpose of these experiments, which, be- 

 ginning in the fall of 1907, were planned to continue for five years 

 upon the same orchards, to learn whether it was possible to redeem 



*Bull. 193, N. Y. State Agr. Exper. Sta., Dec, 1900, p. 355. 



tin another paper of this report, this fact is taken into account in a compu- 

 tation of the product of periods ten days shorter and ten days longer than the 

 above. 



