RELATIONSHIP BETWEEN THE WETTING POWER AND 
EFFICIENCY OF NICOTINE-SULPHATE AND FISH-OIL- 
SOAP SPRAYS 
By Loren B. Smith, 1 
Assistant State Entomologist, and Entomologist, Virginia Truck Experiment Station 
INTRODUCTION 
The influence of the wetting power upon the efficiency of a contact 
insecticide has never been entirely determined, although it has long been 
realized that this quality is an important limiting factor in the efficacy 
of certain sprays in killing insects, especially aphids, whose bodies are 
more or less covered with a waxy secretion. The difficulty of determin¬ 
ing the wetting power of a solution has in the past precluded its con¬ 
sideration in the comparison of contact sprays in the laboratory. The 
present work upon the relationship of wetting power to the efficiency of 
nicotine and soap solutions developed from experiments performed during 
1914 and 1915 in spraying garden peas (Pisum sativum) for the control of 
the green-pea aphid [(Macrosiphum) Acyrtho'siphum pisi Kalt.], spinach 
(Spinacia oleraceae) for the control of the spinach aphid (Myzus persicae 
Sulz.), and strawberries ( Fragaria sp.) for the control of red spiders 
(Tetranychus sp.). The results of the experiments demonstrated that 
the optimum efficiency of sprays containing nicotine sulphate and fish- 
oil soap was reached with a definite degree of concentration 2 and that 
solutions which were more concentrated and also those of lower concen¬ 
tration were less effective in killing the insects. In order to avoid com¬ 
plicated conditions, the following charts of the efficiency of the sprays are 
based altogether on the results of the pea-spraying experiments. The 
proportional efficiency of the sprays against the spinach aphids and red 
spiders was almost identical with the results obtained on the pea aphids. 
When nicotine sulphate and fish-oil soap are mixed before they are 
diluted, under ordinary conditions of temperature, a precipitate may be 
formed. This fact has previously been noted by other authors. 3 The 
composition of the precipitate is probably unknown, although it is gen¬ 
erally supposed that the resulting solutions are less effective killing agents 
than when the materials are mixed in dilute solutions. From observa- 
1 Detailed, by the Virginia Crop Pest Commission for the investigation of insects affecting truck crops. 
2 The terms "concentration” and "concentrated solutions” as used in this paper refer to the amounts of 
materials called for by the various formulae, and not to the original insecticides previous to their dilution, 
unless so stated. 
3 Parker, W. B. The hop aphis in the Pacific region. U. S. Dept. Agr. Bur. Ent. Bui. in, p. 27. 1913. 
Journal of Agricultural Research, 
Dept, of Agriculture, Washington, D. C. 
gg 
(389) 
Vol. VII, No. 9 
Nov. 27, 1916 
Va.—1 
