PLANTS — IUSECTICIDAL PKOPEKTIES. 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 the 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 

 domestiea L.) to the Diptera; the following 17 species of aphids to 

 the Hemiptera: Aphis spp. called A, B, C, D, and E, cabbage aphis 

 (A. trassicae L.), green apple aphis {A. pomi DeG,), nasturtium 

 aphis (A. rumicis L.), A. spiraecola Patch, Macrosiphum spp. called 

 A, B, and G, tulip-tree aphis (M. liriodendri Mon.), rose aphis (M. 

 rosae L.), potato aphis (31. solanifolii Ashm.), chrysanthemum 

 aphis (Macrosiphonella sanborni Gill.), and green peach aphis 

 {Myzus periscae Sulz.) ; the honeybee (Apis mellifica L.) and saw- 

 fly larva (Neurotoma fasciata Norton) to the Hymenoptera ; the 

 silkworm (Bombyx mori L.), catalpa caterpillar (C eratomia catalpae 

 Bdv.), fall webworm (Eyphantria cunea Dru.), and tent caterpillar 

 (Malacosoma amerieana Fab.) to the Lepidoptera; and the roach 

 or croton bug (Bluttella germanica L.) and grasshoppers (Melano- 

 plus femur-iubrum DeG.) to the Orthoptera. 



