18 



miscible oil sprays are recommended as being cheap and effective, and 

 the present paper includes data secured during experiments in 1910 

 which form a basis for comparison between these sprays and those 

 made of fish-oil soa^J. 



Table I records the influence of summer showers upon the efEectiyeness 

 of miscible oil and soap sprays. Experiments showed that miscible 

 oil sprays are scarcely affected by showers, except when these fall 

 immediately after apiDlication. Showers falling 30 minutes after the 

 oil spray had been applied had little effect upon the percentage of 

 larvae and pupae killed, while they had a very evident effect upon the 

 numbers killed by the soap spray. Besides being more resistant to 

 showers, the miscible oil sprays are operative for a longer period after 

 application, even when no showers fall. 



Table II records the re-infestation of foKage two or three weeks 

 after the use of miscible oil and soap sprays. Throughout the summer 

 months adults of both Dialeurodes citri and D. citrifolii are more or 

 less abundant and are depositing eggs. At the time of summer spraying 

 there are but few leaves on infested trees that do not bear a certain 

 number of unhatched eggs of D. citri. It matters little, therefore, how 

 effective an insecticide may be in killing larvae and pupae at the time 

 the spray is applied, if it does not either kill the eggs or operate long 

 enough to kill larvae that subsequently hatch from them. On trees 

 sprayed with fish-oil soap, 9b% of the larvae and pupae were killed, 

 but a sufficiently large number of larvae hatched after the spray was 

 applied to cause blackening of the foliage within a short time. In 

 a similar plantation sprayed with miscible oil, not only were an equally 

 large number of insects killed, but the trees remained free from 

 infestation for a much longer time. Miscible oil used in the strength 

 If per cent, oil was found to have equal killing power with 5 and 8 lb. 

 fish-oil soap to 50 U.S. gals, water, while its effects outlasted a second 

 and third application of the latter spray. When the growers of citrus 

 trees realise that it is more profitable to spray when the numbers 

 of whiteflies on the leaves is still small, the advantage of miscible oil 

 spray over fish-oil soap will be even more apparent in postponing 

 future blackening of the trees and fruit by sooty mould. 



Safro (V. I.). How to test for the Presence of Nicotine on Sprayed 

 Plants. — Jl. Econ. Entoni., Concord, N.H., x, no. 5, October 1917, 

 pp. 459-461. 



Experiments conducted in the autumn of 1916 confirmed the 

 conclusion, which had already been conjectured, that nicotine may be 

 present, and continue to have some action, for a considerable time 

 after the spray has dried and apparently disappeared from the plant. 

 The explanation seems to be that in the evaporation of dilute solutions 

 under ordinary temperatures the water evaporates much more 

 rapidly than _ the nicotine, resulting in a continually increasing 

 concentration of the nicotine film on the sprayed parts of the plant, 

 until finally a very highly concentrated though invisible film of nicotine 

 remains. The actual amount left may be so small as to defy any 

 attempt to determine it quantitatively and yet may show quite 

 distinctly in a qualitative test. The action of this film as an insecticide 

 is as yet undetermined ; it is generally thought that it may act as a 



