REPORT OF THE »JTOMOLOGIST. 



327 



They are: (1) arsenical compounds, (2) petroleum, and (3) pyrethrum. 

 The first act through the stomach, and are effectual chiefly against 

 mandibular insects ; the second and third act by contact, and are, 

 therefore," of more general application, affecting both mandibular and 

 baustellate species. 



The use of arsenic as an insecticide in the field dates from the year 

 1871. At the rate of 50 grains of arseniate of soda and 200 grains of 

 dextrine dissolved in a gallon of water, and this diluted at the rate of 

 about an ounce to ten gallons of water, it furnishes one of the cheapest 

 of insecticides at command, and various patented combinations of it 

 have been extensively sold and used. Again, one pound of arsenic and 

 one pound of sal-soda boiled in one gallon of water till the arsenic is 

 dissolved, and diluted at the rate of one quart to forty gallons of water, 

 is also a good formula. The chief merits of arsenic are cheapness and 

 solubility. Its demerits are its white color, which makes it liable to be 

 mistaken for harmless substances of the same color, and its tendency 

 to burn the plant. Paris green or Scheele's green has been more ex- 

 tensively used than any other arsenical compound, and is, on the whole, 

 one of the most satisfactory insecticides. I first used this poison against 

 the Colorado Potato-beetle (Boryphora 10-lineata) in the summer of 

 18G8, but owing, doubtless, to the use of an inferior article, reported ad- 

 versely upon it. (First Report on Insects of Missouri for 1868, p. 116.) 

 George Liddle, jr., of F airplay, Wis., experimented with it the same sum- 

 mer, and with one part of the green to two of flour, found it eminently 

 satisfactory (American Entomologist, I, p. 219), and from the time he an- 

 nounced his experience — May 25, 1869 — in the Galena, 111., Gazette, the 

 green became rapidly popular against the Doryphora. I first recom- 

 mended it in 1872 for the Cotton-worm, and its use gradually extended 

 to other leaf-eating insects, until hundreds of tons have been sold for 

 insecticide purposes in a single year. It is used dry with various dilu- 

 ents, as ashes, plaster, flour, &c, at the rate of one part of the green 

 (if pure) to twenty-five up to one hundred parts of the diluent. Flour 

 as a diluent has the great advantage of causing greater adhesiveness 

 and permanence. In liquid suspension Paris green can be used at the 

 rate of one pound to from forty up to one hundred gallons of water. 

 The liquid should be kept constantly stirred, and a little dextrine or 

 other substance added to give adhesiveness is an advantage. 



A refuse obtained in the manufacture of aniline dyes, and known as 

 " London purple," is the third important arsenical compound that I 

 will mention in this connection. It consists of lime, arsenious acid and 

 carbonaceous matter, and was first used by me against the Cotton- 

 worm and other insects in 1878, and more fully and thoroughly in 1879. 

 It is used with diluents, either wet or dry, in the same manner as Paris 

 green ; while for some insects experience has shown it to be less satis- 

 factory than Paris green, for many others it is equally effective, and 

 has the great advantage over Paris green of being vastly cheaper 

 (costing on an average but five cents against sixty cents per pound); 

 of covering twice the ground, weight for weight ; of being more sol- 

 uble, less poisonous, more adhesive and permanent in its effects, and of 

 decided color, so that when intelligently used it is in all ways preferable. 



Petroleum, in its various forms, has long been recognized as one of 

 the most effective insecticides in our possession, all oily substances 

 being particularly deadly to insects. Unfortunately, they are also 

 injurious to plants, and one of the problems the solution of which I 

 have had in mind for many years has been their use in such dilution 

 as to kill the insect without injury to the plant. Kelined kerosene 



