October, '17] BACK and Grossman : miscible oils v. soap sprays 457 



foliage within a comparatively short time. In a second grove sprayed 

 with the miscible oil mentioned above, an equally large number of 

 insects were killed, but the grove remained clean, i. e., free from sooty 

 mold on the leaves and fruit, for a very much longer time. Two neigh- 

 boring groves sprayed during late April when the Aleyrodids {citri 

 and citrijolii) were mostly in the early larval stages, one with the mis- 

 cible oil used at the strength of If per cent oil, and the other with fish 

 oil soap, 5 and 8 pounds to 50 gallons of water, perhaps emphasizes 

 the importance of the point in -question more than any large scale 

 work undertaken by the writers. Both groves were sprayed by the 

 writers and Mr. W. W. Yothers with equal thoroughness and with the 

 aid of a power outfit. Results secured about ten days after spraying 

 showed that the fish oil soap at 5 pounds to 50 gallons had killed as 

 many insects as the miscible oil, and it was regretted that fish oil soap 

 had not been used on both groves on account of the saving in the cost 

 of insecticide. However, the grove sprayed with fish oil soap began 

 to blacken and by July required a second spraying and needed a third 

 by October to keep the fruit free from sooty mould. On the other 

 hand, the grove sprayed with the miscible oil remained clean through- 

 out the summer and was blackening in October only in places. 



It is unfortunate that the percentage of larvae and pupse killed by 

 the oil and soap sprays, given in Table II, are not more alike as there 

 may be those who will think the much larger average number per 

 leaf of living first and second instar larvae, found on the leaves two to 

 three weeks after spraying, is the direct result of the comparatively 

 small number of forms killed by the fish oil soap at the time of applica- 

 tion. It is possible, and more than probable, that in any grove so 

 heavily infested, even if practically all the forms had been killed by the 

 sprays at time of application, a certain amount of reinfestation from 

 without would occur as migrating adults are quite active and may 

 begin ovipositing within a day after emergence. However, the rows 

 of trees sprayed with both oil and soap sprays were equally subject 

 to reinfestation. No examinations for the first and second instar 

 living larvae were made until two to three weeks after the spraying in 

 order to give the insects in these instars when the spray was applied, 

 and that escaped the action of the spray, an opportunity to develop 

 into third instar larvae. Studies of the biology of citri (1) have proved 

 that during the summer months the egg stage averages 10-12 days; 

 the first larval, 7.2 days; and the second larval, 5.4 days. The corre- 

 sponding instars of citrifolii are a trifle longer. These facts make it 

 certain that the first and second instar larvae recorded as living are 

 those which hatched from the eggs present on the foliage when it was 

 sprayed, or from a relatively small number of eggs deposited after 

 spraying. 



