be made before they become abundant enough to do injury. Unless 

 the insects are actually touched by the mixtures, they will not be 

 harmed; it is therefore important that they should not be allowed 

 to become numerous enough to curl the leaves, to form a protection 

 for the specimens beneath them. Two or three applicatiops of 

 moderate strength at short intervals are better than a single appli- 

 cation of a strength that is dangerous to foliage. 



If whale oil soap is not available, laundry soaps may be used and 

 particularly those that contain a percentage of naphtha or kerosene. 

 There are several soaps of that kind on the market, and they are almost 

 as effective as the fish oil combinations. Greater care must be taken 

 with ordinary laundry soaps than with either of the others. 



Potted plants, if they are treated with soaps, should have the surface 

 of the ground protected that the suds may not get into it. If the soap 

 is emulsified with soda, as it usually is, this will poison the roots of 

 the plants if it gets to them. Outdoors no reasonable application is 

 likely to influence the soil. 



Shade trees, when of any considerable size, cannot often be satis- 

 factorily treated for plant lice, because it is almost impossible to 

 reach all the insects ; but if they are of moderate size and the infesta- 

 tion is bad, fish oil soap offers the best chance for good results. 



Natnral Enemies. 



Plant lice have many natural enemies and their increase dejiends 

 largely upon weather conditions, but there is no one condition which 

 is uniformly favorable or unfavorable to all. Some thrive during hot, 

 dry weather; others do better in a season that is cold and moist. The 

 latter conditions favor the development of that species which is so 

 abundant upon the Norway maples early in the season, and usually 

 after a cold, wet spring a change that results in a few days of hot, dry 

 weather will mark the end of the attack upon that foliage. 



It vidll be always noted that whenever plant lice increase abnormally 

 their predatory and parasitic enemies also increase, and that some- 

 where about the middle of the season the tendency is to re-establish 

 a balance, the plant lice decreasing to normal numbers. This does not 

 apply in all cases, but may be considered a rule, yet there can be no 

 dependence upon these insect enemies; whenever an injurious species 

 increases to such an extent as to threaten harm, destroy it, if at all 

 possible. 



