214 JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY. 
by Prof. Smith and others with variations of his original ' nicodust,' which is 
obtained by impregnating finely pulverized kaolin with ' Blackleaf 40.' 
Various admixtures of nicodust with sulphur, arsenical compounds, and 
fungicides are also being prepared. At the present time lime has practically 
replaced kaolin, as it liberates the volatile nicotine more readily, and the addition 
of dry sulphur at mixing time appears to increase the efficiency of the dust. 
Summarizing the results of available experimental data, the author recom- 
mends a dust composed of 5 per cent, or 6 per cent. ' Blackleaf 40 ' for most 
common aphides. A 2 per cent. ' Blackleaf 40 ' dust was adequate for the walnut 
aphis (Chromaphis juglandicola Kalt). It is of doubtful use against aphides with 
a waxy or mealy protective covering. 
For grape-leaf hopper (Erythroneura comes) demonstrations indicated that 
a 6 per cent, dust would kill all nymphs, but a 10 per cent, dust was required 
to destroy adults. The false chinch bug (Nysius ericae Schilling) in one instance 
at least was controlled by a 6 per cent. dust. Young hairy caterpillars readily 
succumb to nicodust. It is also said that mixtures of nicodust and arsenate 
of lead were very efficient in controlling caterpillars and flea beetles. — G. W. G. 
Insecticides, Petroleum. By R. K. Vickery (Jour. Econ. Entom. vol. xiii. 
pp. 444-447 ; Dec. 1920). — The author refers to the millions of gallons of oil 
now being used as insecticides in relation to the Government warning fore- 
telling the rapid depletion of the American petroleum resources. It is pointed 
out that a shortage would raise the price sufficiently to make petroleum un- 
available as an insecticide. Many of the household and industrial oils, such 
as kerosene, crude oil, lubricants, and the by-product distillates make efficient 
sprays ; and in consequence the study of the toxicology of petroleum to insects 
has been somewhat neglected. Shafer and others have shown that petroleum 
is a true chemical poison, but it is not known what compounds in petroleum 
are actually toxic to insects. 
Economic demand might make it profitable to prepare these compounds 
synthetically. Moore has drawn attention to the fact that the spiracles are 
the weakest link in the insect's armour against contact insecticides, and has 
shown that the heavy vapours of petroleum, and other volatile contact insecticides, 
are the most efficient. These heavy gases condense on the walls of the trachea, 
and it has been suggested petroleum kills by upsetting the balance between the 
oxidizing and reducing enzymes in the body fluid. A knowledge of the chemistry 
of petroleum may make it possible to find compounds fatal to insects and not 
injurious to plants. 
A history of petroleum sprays shows the gradual development of methods 
to protect the plant from the injury caused by the commercial oils. Emulsion 
made it possible to dilute the oil with water. Miscible oil made the soap emulsion 
a commercial proposition ; but unfortunately the miscible oil formula is not 
adapted to the heavy oils. The latest improvements have been with colloidal 
emulsions, which, being chemically inert, will mix with hard water, lime-sulphur 
solution, arsenates etc. 
Modern synthetic chemistry is making available many compounds, some of 
which are undoubtedly toxic to insects. The scarcity of petroleum is likely to 
make it profitable to hunt out these products. The ideal contact insecticide 
should be an active insect poison, harmless to the most tender foliage. It 
should keep well and be usable as a wash or as a dust. The article is concluded 
with a bibliography on the subject. — G. W. G. 
Insecticide, Some Notes on a New and Promising. By E. N. Cory (Journ. 
Econ. Entom. vol. xiv. pp. 345-347, Aug. 1921). — These notes refer to an alcoholic 
extract of pyrethrum prepared in the form of a heavy liquid soap, which mixes 
readily with water, spreads evenly, and sticks fairly well. 
Rose aphis and the bean aphis were easily killed at a dilution of 1 to 100 ; 
and nearly complete control appears to have been obtained with a dilution up 
to 1-2000 on chrysanthemums infested with brown aphis. Tests made with a 
tent caterpillar (Malacosoma americana Fabre) at 1 to 600 killed all full-grown 
larvae, although death in some cases was slow. 
The wash has a decided repellent and possibly some toxic action. At 1-100 
mealy bugs (P sen do coccus citri) were uninjured, and results on red spider were 
similarly unsatisfactory. As might be expected, the wash is an exceedingly safe 
one, and is said not to spot the most delicate flowers at normal dilutions. — G. W. G. 
Insects on Grasses and their relation to Cultivated Crops, Observations on the. 
By H. W. Miles (Ann. App. Biol. vol. viii. Nos. 3-4, Nov. 1921, pp. 170- 
181). — An investigation into the occurrence of insect pests among the vegetation 
of headlands, hedgerows, and waste places surrounding farm land in Shropshire. 
