August, '11] IMORRILL: WHITEFLY CONTROL 373 



should not interlock since this seriously interferes with both fumigation 

 and spraying. 



Briefly stated, citrus groves should be made to conform to the re- 

 quirements of effective and economical whitefly control regardless 

 of the apparent sacrifices. To illustrate the situation: If the normal 

 annual rainfall in Florida were to be decreased from fifty inches to ten 

 inches a radical change in the methods of producing a citrus crop 

 would be required and the fact that comparatively few citrus groves are 

 at present piped or trenched would not make irrigation impracticable 

 or any the less effective. Similarly the fact that many citrus groves 

 in Florida are at present very poorly adapted to the use of direct 

 remedies for whiteflies does not detract from the availability of these 

 remedies or furnish a sound argument against the adoption of a 

 systematic campaign for whitefly control along the lines outUned in 

 this paper. 



The Search for Enemies of the Citrus Whitefly as Affecting the 

 Desirability of Immediate Action toward Control by Direct 

 Means 



For years Florida citrus growers have been interested in the possi- 

 bility of foreign explorations locating the original home of the citrus 

 whitefly and in the possibility of discovering there effective natural 

 enemies. In the investigations of whiteflies begun in 1906 efforts in 

 this line have naturally been preceded by field investigations which were 

 certain to give practical results. The principal results of these inves- 

 tigations are now being published by the Bureau of Entomology. As 

 a result of our present knowledge of the whiteflies, contributed to by 

 the investigations of the United States Department of Agriculture 

 and by the Florida Experiment Station, citrus growers in Florida are 

 now confronted by the opportunity to begin at once a practicable 

 organized effort to bring the whiteflies into a state of control. The 

 question naturally arises: Is such an undertaking advisable as long 

 as there exists the possibility of discovering and introducing an effec- 

 tive natural enemy? This can be determined only by means of an 

 examination of the history of similar efforts to discover and introduce 

 beneficial insects. The following facts and conclusions are based upon 

 an examination of most of the important literature on this subject: 



1. There are on record more failures than successes in the endeavors 

 made in the various parts of the world to control imported insect pests 

 by means of natural enemies secured by foreign explorations. 



2. The success of the Australian lady bug (Novius cardinalis) in 

 controlling the cottony cushion scale in California, resulting in com- 

 plete commercial control within a few months after its introduction^ 



