238 HORTICULTURE FOR SCHOOLS 



350. San Jose scale. If the twigs or even the larger 

 limbs and trunks of a tree infested by San Jose scale are 

 examined in the winter, little black or gray scales varying in 

 size from almost microscopic to about one-sixteenth of an 

 inch in diameter may be seen. By raising one of these scales 

 with the point of a knife, the little yellow body of the insect 

 may be discovered underneath. 



While there is an egg stage of this insect, the eggs are not 

 laid but hatch within the body, and the young are born alive. 

 At first they have the ability to travel about over the tree 

 by means of six little legs. In a very short time, however, 

 they become attached to foliage, fruit, or twigs by means of 

 their beaks. The legs disappear and the power of locomotion 

 is lost. Throughout the remainder of the life of the female 

 insect, no movement from one place to another occurs. In 

 the case of males, wings are developed which enable them 

 to fly for some little distance. 



Control of the armored scales is usually by means of a 

 thorough application of lime-sulfur spray at the strength of 

 1 gallon of lime-sulfur to 10 gallons of water, or by using some 

 form of oil emulsion spray. In California, where the black 

 scale is a serious pest of citrus trees, fumigation with hydro- 

 cyanic acid gas introduced under a tent placed over the tree 

 is the remedy. 



Many insects have natural enemies which tend to keep 

 them in check. The eggs of a parasitic insect are shown 

 in Fig. 122, attached to a larva. These eggs will hatch 

 and in the course of time will destroy the host. The pre- 

 daceous insects, some of which are shown in Fig. 123, 

 devour aphids and scale insects and other forms, and 

 thereby assist greatly in the work of control. 



351. Plant-lice (Fig. 124). There is scarcely a plant that 

 is not attacked by one or more species of little soft-bodied 

 insects called plant-lice or aphids. They derive their nour- 

 ishment from the plants by sucking it from the tissues through 



