INSECTS INJURIOUS TO ORCHARD TREES 437 



have gained an entrance before they have had time to do 

 much injury. A heavy coating of whitewash kept over the 

 trunk of the trees during the summer affords much protection. 



There is also a flat-headed borer that works in the trees 

 in much the same way, and can be controlled by the same 

 methods. 



The Periodical Cicada (Cicada septemdecim) . It is com- 

 monly supposed that cicadas do much damage to the orchard 

 trees. As a matter of fact, however, the injury that they cause 

 is not particularly serious except to young trees. When the 

 female is laying her eggs she makes rather large holes or wounds 

 in the bark with her ovipositor. As soon as the young hatch 

 they drop to the ground and bury themselves in the soil 

 where they feed on roots and other substances for more than 

 sixteen years, finally changing to the pupae or nymphs. Then, 

 seventeen years after the eggs have been laid, they issue 

 as the adult cicadas, which soon lay their eggs and die. As 

 there may be more than one brood in a locality with different 

 times of emergence it is not always seventeen years between 

 the outbreaks. Government bulletins giving dates upon which 

 all the various broods occurring in the United States may be 

 expected to issue, can be obtained by making application as 

 suggested on page 420. 



There are other species of cicadas that complete their 

 development in much less time. Although these insects do 

 not at all resemble grasshoppers, the two have been confused 

 under the term locust, the periodical cicada often being re- 

 ferred to as the seventeen-year locust; the term locust, how- 

 ever, is properly applied only to the grasshoppers. 



APHIDS, OR PLANT-LICE 



In structure and habits the plant-lice (family Aphidida) 

 are among the most interesting of our insects. They are all 

 very small and soft-bodied, and feed upon the leaves or stems 

 of plants, sucking the sap by means of a long slender beak. 

 Their life history is subject to considerable variation among 

 the different species, but they all agree in certain features. 



