BIOLOGY AND HUMAN WELFARE 



411 



has spread all over the United States. The adult female insect 

 lies permanently attached by its beak to the bark, underneath 

 a tiny waxy scale which it secretes. Here eyes, legs, and antennae 

 are lost and the sac-like creature sucks the plant sap and repro- 

 duces. It is estimated that the progeny of a single individual 

 during one season would number thirty million if all were to sur- 

 vive. (Fig. 264.) 



About forty years ago the vineyards of France, and later those 

 of California, appeared to be doomed to destruction by the attacks 

 of a species of minute plant lice, or Aphids. The French govern- 

 ment offered a large reward for an effective remedy, and many 

 entomologists and botanists devoted all their time to the study 

 of the problem. Eventually it was discovered that certain Ameri- 

 can wild Grapes were naturally immune to the pest. Accordingly 

 by grafting the cultivated grape upon the resistant wild stock a 

 combination was effected which saved the vineyards of both coun- 

 tries. (Figs. 222, 265.) 



The Mediterranean Fruit Fly appeared a few years ago in 

 certain Florida orchards but the invasion apparently has been 

 repulsed by the vigilance of the 

 United States Bureau of Ento- 

 mology and Plant Quarantine. 

 It is the larvae of the fly that 

 are the mischief-makers, because 

 when they develop from eggs de- 

 posited in the fruit they soon ren- 

 der it unfit for human food. When 

 we realize that the annual fruit 

 and vegetable crop of Florida 

 amounts to well over a hundred 

 million dollars, it is no wonder 

 that this fly is one of our most 

 notorious foreign emigrants. But Fig. 261. — Mediterranean Fruit 



we maintain a defense on the Rio £Iy, keratitis capitata. (From U. S. 

 „ , . __ . Department oi Agriculture.) 



Grande against the Mexican t ruit 



Fly, and others throughout the country against our many native 



species of Fruit Flies, though the latter are held in check to a 



considerable extent by their own insect enemies. (Fig. 261.) 



Another great problem is the preservation of forest and shade 



trees from native and also imported pests. The enormity of the 



