PLANTS — INSECnCIDAL PKOPERTIES. 3 
for dusting it should be very fine, at least fine enough to pass through 
a sieve having 60 meshes to the inch. If it is to be extracted such 
fineness is not always necessary. Cold-water extracts are best pre- 
pared by macerating the material in water for several days or longer, 
then filtering or straining, and making the aqueous extract up to the 
desired volume with more water. The cold-water method is necessary 
in the case of material which will decompose if heated. Decoctions, 
or hot-water extracts, are best made by boiling the ground material 
with water or percolating boiling water through it. These extracts 
may be concentrated, if necessary, to any desired volume by evaporat- 
ing under reduced pressure (less than one atmosphere) on a steam 
bath. Plant material which can be used with satisfactory results as 
a powder or as a water extract may be sold in the powder form, with 
directions for use, because the preparation of the water extract, either 
hot or cold, is a simple process. 
In many cases, however, the plant constituent which has the desired 
insecticidal effect can not be removed with water, but requires some 
organic solvent to effect its solution. In these cases the plant ma- 
terial is macerated or percolated with the desired solvent, either with 
or without heat, according to the nature of the active constituent. 
From the extracts obtained the solvents must be removed by distilla- 
tion under reduced pressure. The concentrated extract must then be 
incorporated into a watery spray mixture. Since extracts made by 
means of alcohol, benzene, gasoline, or other organic solvents are 
usually insoluble in water, a special procedure is necessary to make a 
spray solution in which the organic extract is held in a fine and fairly 
stable suspension. The best method must usually be determined by 
trial for each individual case. In most cases tha semisolid extract 
can be triturated with soft soap and water gradually incorporated so 
that a suspension of finely divided but undissolved particles results, 
giving the spray mixture a milky or muddy appearance. Frequent 
shaking will keep the mixture uniform in the sprayer. 
INSECTS EMPLOYED AND METHODS OF TESTING 
PREPARATIONS AGAINST THEM. 
In all, 28 species of insects were tested — the squash lady-beetle 
(Epilachna borealis Fab.) and Colorado potato beetle (Leptinotarsa 
decemlineata Say) belonging to the Coleoptera; the house fly (Musca 
domestica L.) to the Diptera; the following 17 species of aphids to 
the Hemiptera: Aphis spp. called A, B, 0, D, and E, cabbage aphis 
(A. brassicae L.), green apple aphis (A. pomi DeG.), nasturtium 
aphis (A. rumicis L.), A. spiraecola Patch, Macrosiphum spp. called 
A, B, and C, tulip-tree aphis (M. liriodendri Mon.), rose aphis (J/. 
rosae L.), potato aphis (M. solanifolii Ashm.), chrysanthemum 
aphis (MacrosiphoneJla sanborni Gill.), and green peach aphis 
{Myzus periscae Sulz.) ; the honej^bee {Apis tnellificd L.) and saw- 
fly larva (Neurotoma fasciata -Norton) to the Hymenoptera ; the 
silkworm {Bombyx mon'L), catalpa caterpillar (Ceratomia catalpae 
Bdv.), fall webworm (Hyphantria ainea Dm.), and tent caterpillar 
(Malacosoma a?nericana Fab.) to the Lepidoptera ; and the roach 
or croton bug {Blattella gcrmanica L.) and grasshoppers (Melano- 
plus femur- rubrum DeG.) to the Orthoptera. 
