518 INSECT PESTS OF FARM, GARDEN AND ORCHARD 



females, which are deposited on the trunk of the tree. The 

 sexes are wingless, much smaller than the summer forms, and 

 are without beaks, so that they take no food. The female is 

 a brown-ochre color, and the male dark green or greenish- 

 brown and smaller, as shown in Fig. 448. They become full 

 grown in about eight days, when they mate and the female then 



FIG. 447. Sexual female of the woolly apple-aphis, showing egg before and 

 after extrusion greatly enlarged. (After Alwood.) 



lays a single large black egg, which is deposited in the crevices 

 of the bark on the lower part of the trunk. These eggs hatch 

 in the spring and give rise to new colonies. 



As they multiply large galls are produced on the roots, the 

 tissue probably being poisoned by the mouth-parts of the insects. 

 As a result the roots soon die and the aphids then migrate to 

 the growing roots, so that their absence on the worst knotted 

 roots does not indicate that they have forsaken the tree but that 

 they are on younger roots, 



Control. Nurserymen commonly apply a liberal amount of 

 tobacco dust in trenches along the rows, which kills the aphids 

 and acts as a repellant, as well as being worth half its cost as a 

 fertilizer. This is probably the best practice in the nursery unless 

 the aphids become abundant, when more vigorous treatment 

 should be used, but tobacco has not always proven a satisfactory 

 treatment for orchard trees, though used with apparent success 



