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JOURNAL OF ECONOMIC ENTOMOLOGY 



[Vol. 10 



no showers fall. Foliage sprayed with miscible oils remained slightly 

 oily both in appearance and to the touch for several weeks after the 

 sprays had been applied. Fish oil soap leaves no such evidence that 

 the trees had been sprayed. In experimental work on a large scale, it 

 became quite evident that the miscible oil sprays used were giving better 

 results than the soap sprays. An examination into the subject proved 

 that the greater efficiency of the oil spray seemed not to be due to a 

 higher percentage killed of the larvae and pupae on the leaves when 

 the spray was applied at the proper strength, but to the effect these 

 insecticides had upon unhatched eggs or the young larvae hatching 

 therefrom within ten days to two weeks after application. The data 

 in Table II represent the condition of the white flies in adjoining rows 

 of the same badly infested grove during the summer of 1910. 



Table IL — Reinfestation op Foliage Following Use op Miscible Oil and Soap Sprats 



The examinations upon which the data of Table II are based, were 

 made between two and three weeks after the application of the spray. 

 At all times during the summer months adults of both Dialeurodes 

 citri and D. citrifolii are more or less abundant and depositing eggs. 

 At times of summer spraying there are comparatively few leaves on 

 infested trees, especially those infested by citri, that do not bear un- 

 hatched eggs in varying numbers. Those in touch with the white 

 fly problems appreciate the fact that no matter how effective an insec- 

 ticide may be in killing larvae and pupae on the leaves at the time the 

 spray is applied, if it does not either kill these unhatched eggs or is 

 operative long enough to kill larvae that subsequently hatch, much of 

 the benefit of the spraying is counterbalanced by the reinfestation 

 thus brought about. In one grove in which 95 per cent of the larvae 

 and pupae were killed by fish oil soap, a sufficiently large number of 

 larvae hatched after the spray was applied to cause a blackening of the 



