256 THE CHIEF SOUTHERN AGRICULTURAL CROPS 



natural enemies that aid materially in holding them 

 in check. They are attacked by minute Hymenop- 

 terous parasites, are eaten greedily by various species 

 of ladybirds (^Coccinellidce) and by certain predaceous 

 Lepidopterous larvce, and in moist regions they are 

 frequently destroyed by various insectivorous fungi. 

 In fact, it may almost be considered a rule that in its 

 native country each scale insect has developed so 

 many natural enemies that under normal conditions 

 it is kept so closely under control as to do but little 

 real damage. Sometimes, however, changes in weather 

 conditions or in other factors favor tlie scales at the 

 expense of their enemies with disastrous results. 

 Most of the worst outbreaks have occurred when scales 

 have been accidentally imported from one country to 

 another and have thus been able to escape their 

 natural enemies. A striking instance of this kind 

 was the outbreak of the cottony-cushion scale that 

 at one time suddenly threatened to extinguish the 

 California orange industry. The absolute destruction 

 of this scale which followed so promptly after the intro- 

 duction of its natural enemy, the Australian ladybird 

 (Vedalia)^ was one of the most spectacular triumphs 

 of modern economic entomology. Aside from this 

 introduction of natural enemies two lines of treatment 

 are recognized for scale insects: spraying with caustic 

 contact poisons like kerosene emulsion, whale-oil soap, 

 or the rosin-lime mixtures, or fumigating with hydro- 

 cyanic-acid gas. Spraying is much more difficult 

 and unsatisfactory than with deciduous trees, and 

 the fumigation is costly and unless done with 

 great care dangerous. Both treatments have the 



