SCALE-INSECTS. 35 



23. Tobacco. A good remedy against larvae and adults; 



doubtful against the eggs. Fumigation has 110 effect 

 on scale-insects, except sometimes on Dactylopidse, 

 or " mealy bugs " (Hubbard ; Comstock ; Personal 

 experiment). The tobacco should be applied in a 

 pretty strong solution ; but the expense in this 

 country would be probably too great for general use.. 



24. Whale-oil and whale-oil soap have been already alluded 



to under the head " Kerosene." They are both useful 

 ingredients in mixture with that substance, if pro- 

 curable cheaply. 



From the foregoing list it will be gathered that, if experi- 

 ment, combined with knowledge of the habits and life-history of 

 scale-insects, can be relied on, there is no substance better 

 adapted for their destruction than kerosene, mixed with oil, or 

 milk, or soap solution, and carefully applied. It has been 

 already observed that the killing of the eggs is absolutely 

 necessary for thorough clearing-away of the insects ; and, to 

 quote again the words of Mr. Hubbard, kerosene is " almost 

 the only substance which will with certainty kill the eggs with-: 

 out at the same time destroying the plant. " 



But precautions must not be neglected. Persons who reck- 

 lessly use any remedy, or who apply it too thickly or in too 

 strong proportions, must expect their trees to suffer. Nor 

 must the weather and the time of the year be overlooked. 

 Winter is the best season for all remedies ; and, preferably, cool 

 and cloudy days. Again, if substances soluble in water, such 

 as potash or soda lye, soap solutions, &c., be employed, it must 

 be expected that a day's rain will wash a good deal of them off, 

 and greatly reduce their efficacy. These are things which many 

 people forget ; they fancy that because somebody has cleared 

 his trees with, say, castor-oil in winter they can do the same 

 thing in full heat of summer; or, because a lye solution has 

 done well in the dry climate of California, that it will be 

 equally good in the rains of New Zealand. Still more is it a 

 fallacy to imagine that rule-of -thumb methods, not founded upon 

 any knowledge of the nature, habits, and life-history of the 

 insects, are likely to be really efficacious. 



Little need be said here of a remedy which has had, to some 

 extent, the authority of Professor Riley, and which is recom- 

 mended by Mr. Howard (Report U.S. Dep. of Agric. 1880-81, 



