78 POPULAR FRUIT GROWING. 



and kerosene emulsion). The bodies of leaf lice, which form 

 a considerable portion of this class of insects, are covered with 

 a thin skin and are injured or killed by astringent solutions, 

 such as tobacco water, and also by hot water. Fumigating with 

 hydrocyanic acid gas in case of scale or other sucking insects 

 is a good remedy. Fumigating with tobacco smoke will kill most 

 kinds of leaf lice. In fact, it would seem that fumigation, be- 

 ing so sure a remedy, is destined to be more largely used in the 

 future. The use of strong compounds, when trees are dormant, 

 for the destruction of scale insects, must continue to gain in 

 popularity. Among the best of the compounds used for this 

 purpose are the lime and sulfur mixture and the soluble oil 

 preparations. 



Insects that attach themselves to roots generally are of the 

 sucking class and are extr-emely difficult to destroy. Among 

 the worst of these pests is the woolly aphis or root louse of the 

 apple, and the phylloxera or root louse of the grape, the latter 

 having been extremely injurious to the roots of the European 

 Wine Grape in France. In the case of the woolly aphis the 

 trouble is largely avoided by planting trees that are known to 

 be exempt from it. If the trees are once well started there is 

 little danger of injury, since the pest is seldom harmful to large 

 trees. Fumigation of stock insures the removal of the root 

 louse. In the case of the phylloxera on the European Wine 

 Grape the only satisfactory remedy has been to graft on the 

 roots of some resistant stock such as the American Frost Grape 

 (Vitis riparia). So common has this practice become in Europe 

 that the result is the European wine industry stands on Ameri- 

 can roots. 



Beneficial insects. In a state of nature, each species of the 

 animal kingdom is held in check so there is a nicely balanced 

 relation between them, but occasionally even in nature some 

 one species becomes too numerous and breaks the bounds that 

 are ordinarily strong enough to hold it. Among the natural 

 agencies that destroy insects may be mentioned heavy rains, 

 sudden changes to a freezing temperature, winds, predaceous and 

 parasitic insects, and fungous and bacterial diseases. 



Parasites. A most important factor in checking the spread 



