1907.] The Cottony Maple Scale in Illinois. 359 



3. The area injuriously infested by this insect in Illinois last 

 year covers parts of at least fifteen counties, distributed throughout 

 the state from the Wisconsin line to Marion county. 



4- The chief food plant is the soft maple, but linden and box- 

 elder are almost equally liable to infestation. The elm and the 

 honey-locust are the principal other ornamental trees subject to 

 serious injury. 



5- There is but one generation of this insect each year. The fe- 

 males pass the winter partly grown on the twigs of trees, and pro- 

 duce eggs in late May or in June, according to the latitude and the 

 weather of the season. These eggs hatch in June and July, the 

 young insects establishing themselves for the summer on the leaves 

 or twigs, from which they suck the sap. The males emerge as 

 winged insects, and perish at the approach of winter. The females 

 at that time collect on the twigs and smaller branches for hibernation. 



6. The most useful insecticide is kerosene emulsion, which, if 

 used in summer, should not contain more than 10, or possibly 121^, 

 per cent, of kerosene, and, if used in winter, not more than 16 to 18 

 per cent. As a summer spray this emulsion must be used twice in 

 succession, with a ten-day interval between sprayings. The first 

 application must be made when about half the eggs are hatched, and 

 the second at about the end of the hatching period. Two treatments 

 with 10 per cent, kerosene, applied to badly infested trees in Chi- 

 cago, the first July 11 and the second July 20, 1905, destroyed 82 

 per cent, of the scales ; a single treatment July 1 1 destroyed 64 per 

 cent. ; and one July 19, 68 per cent. A similar treatment July 3,^ 

 on the other hand, killed but 33 per cent, of the insects. 



7. A single treatment in winter with a 19 or 20 per cent, emul- 

 sion destroyed more scales than two summer treatments with a 10 

 per cent, emulsion, the percentages of killed varying from 86 to 

 91 per cent. 



8. Where large trees weakened by unfavorable conditions or by 

 insect attack are treated with strong emulsions in winter, they are 

 liable to injury by a penetration of the kerosene to the roots. Such. 

 trees should be protected, consequently, by covering the earth be- 

 neath the trees with sheets of canvas or layers of straw, or some 

 similar absorbent substance. 



9. Kerosene emulsion is made as follows : Dissolve one pound 

 of common soap, or half a pound of whale-oil soap, in one gallon of 

 water by boiling, remove from the fire, and add two gallons of kero- 

 sene. Then with a spray pump force the mixture back into itself 

 for about five minutes, or until it presents the appearance of a thick 

 cream and no longer separates on standing. This is the undiluted 



