SUMMARY AND CONCLUSIONS. 73 



ill llio lino of \vhit(^-lly coiUrol. It sliouM ho homo in miiul that 

 evoii thousjjli an iini)()rtant and succosslul oiuMiiy should J)o discov- 

 ered A\itliiu the lU'xt two 3-ears, it would prohahly require several 

 years before the ])ractical results secured would justif\^ the abandon- 

 ment of artificial methods of control. On the other hand, in planning 

 for the future the j)roj)ortion of successes and failures of the past in 

 obtaining successful natural enemies for various pests must be con- 

 sidered. Instances of such comj^leto success as was obtained by 

 the introduction of the Australian ladybird into ('alifornia and later 

 into Florida for the control of the cottony cushion scale are rare. 

 Instances of only partial success or of entire failure are many. It is 

 true that many failures have been due to the elementary condition 

 of our knowledge of insect parasitology and that the failures of 

 to-day and of the past ma}' l)e overcome by advances in this line 

 which may be inado in the future. The field is almost unUmited 

 in ])ossibilities, and even the failure of tlie present foreign explora- 

 tions should not lead to the abandonment of all hope of successful 

 natural control. 



