I20 



AN ECONOMIC ENTOMOLOGY. 



really necessary, since the treatment to be adopted is nearly the 

 same in all cases. On deciduous trees, where the scales remain 

 during the winter upon trunks and branches, and where the trees 

 become dormant, the scales are best treated during the winter. 

 At that time there is no foliage to interfere, and we can use much 

 stronger washes than would be safe during the summer, or when 

 the tree is active. I have already called attention to the fact that 

 it is difficult to penetrate insect tissues with ordinary liquids, and 

 it has been found impossible in practice to obtain good results in 

 the destruction of scale insects except by means of caustics. 



against the scurfy scale, while common laundry soap has been 

 efficient against others of the softer species. The common soaps 

 are all caustic, and, when applied at the strength indicated, the 

 scale is shrivelled, lifted, and partially corroded, so that the oily 

 mixture works its way beneath, into absolute contact with the 

 insect. Or it is raised at the edges and washed off by the rains, 

 carrying with it either eggs or young, as the case may be. In 

 fact, where the eggs hibernate winter applications act only by 

 exposing them, so that they are easily washed away by rains and 

 scattered, under no proper condition to hatch. Or, should they 

 hatch, the larvae are able in rare instances only to get upon the 



The scurfy scale, Chionaspis fiirfuriis. — a, twig 

 infested by female scales ; b, with male scales ; c, 

 female; d, male scale, much enlarged. 



Fig. 90. 



Potash and soda have 

 been used wath good effect 

 even in a simple watery 

 mixture, but more satis- 

 factorily in the form of 

 very caustic soap. Whale, 

 or other fish-oil soap, at 

 the rate of two pounds in 

 one gallon of water, as a 

 winter wash, has proved 

 absolutely effective against 

 the San Jos6 scale and the 

 oyster-shell bark-louse, 

 two of the most resistant 

 of the armored scales. 

 The simple muriate of 

 potash used as a fertil- 

 izer has proved effective 



