wor.'i The Cottony Maple Scale in Illinois. 349 



The Hatching Period. 



As the newly hatched young are especially susceptible to the 

 petroleum insecticides, which act by contact, a definite knowledge 

 of the hatching period has an important practical value. In central 

 Illinois this period extends approximately from June 1 5 to July 20. 

 In and about Chicago it commonly begins about two weeks later, 

 and continues for a period of three weeks, this retardation being ap- 

 parently due to the higher latitude and to the neighborhood of Lake 

 Michigan. In 1905, for example, Dr. Folsom found that the young 

 began to appear in Chicago about July i, and were all out by 

 July 21 or a few days later, but that thirty miles west of the 

 city, hatching began about June 20. Mr. H. E. Weed reports, in 

 Bull. 52 of the U. S. Bureau of Entomology, that in 1904 scarcely 

 any eggs had Jiatched in Chicago^by June 25, but that the young ap- 

 peared rapidly under the influence of a few days of warm weather, 

 about July 10. The recorded dates for Colorado approach those 

 given for Chicago. In Washington, D. C, according to Dr. How- 

 ard, hatching of the eggs begins usually in late May or early June, 

 and continues into July and sometimes to the beginning of August. 



The period varies, in short, as to its beginning time, with the 

 advancement of the season, and once begun, the rapidity of the 

 hatching will depend, other things being equal, on the warmth of 

 the weather. It is also influenced locally by the amount of foliage 

 on the trees, the eggs hatching later and more slowly in a dense 

 tree-top than in one more open to the sun. 



Summer Insecticide Measures. 



Owing to the manner in which these insects obtain their food — 

 that is, by sucking the sap through a tubular beak— they are not 

 susceptible to poisoning by way of their food, and the only insecticides 

 available against them are those which kill by contact, and of these 

 the kerosene mixtures have thus far been found the most useful. 

 The most satisfactory of these is the common kerosene emulsion, 

 made by thoroughly and intimately mixing a good grade of kero- 

 sene with one third its volume of a strong soap-suds, and diluting 

 with water according to the time of the year when used. Precise 

 directions for preparing and applying this emulsion may be found m 

 the general summary at the end of this paper. 



The use of this insecticide for the maple scale dates from experi- 

 ments made by me in 1884, intended to test the effect of kerosene 

 emulsion on the newly hatched young, and described in the Four- 

 teenth Report of the Illinois State Entomologist. They showed 



