ANIMAL BIOLOGY 



but despite efforts to check its spread it has become scat- 

 tered through most of the United States. An allied species 

 is a destructive enemy of orange and lemon trees. In 

 some species the female retains the power of locomotion 

 throughout life and possesses eyes, antennae and legs. 

 One of the less degenerate scale bugs is the cottony-cush- 

 ion scale which secretes a cottony mass of fibers within 

 which it deposits its eggs. This insect was introduced 

 into California from Australia, and spread with such great 



rapidity that it threatened to 

 exterminate the orange groves. 

 An entomologist, Mr. Koebele, 

 was commissioned to search for 

 the enemies of the cottony- 

 cushion scale in its native 

 country and to import any 

 species which might prove a 

 means of checking the alarming 

 spread of this pest. This search 

 FIG. 30. Scurfy bark-louse, resulted in the importation of a 



d, male; c, female. (After . , _ . 



Howard.) beetle, Novius (Vedaha) cardi- 



nalis, which thrived and mul- 

 tiplied to such a degree that it effectively exterminated 

 nearly all of the scale bugs of this species. Other scale 

 bugs are combatted by spraying trees with kerosene emul- 

 sions and other insecticides, and by covering the trees with 

 tents in which poisonous gases are generated in sufficient 

 quantity to prove fatal to the insects without severely 

 injuring the trees. All of these measures are expensive, 

 but they are less costly than the damage done by the in- 

 sects. Directly or indirectly the scale insects entail a loss 

 of many millions a year. On the other hand there are a 

 few species which are of economic value, such as the 

 cochineal insect which feeds upon cactus in Mexico and 



