. Economic entomology for the 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
. Economic entomology for the 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 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
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