Part II. Insects. 



1. Potato beetle. {Doryphora decemlineata, Say.) This in- 

 sect is too well known to require description. During the past 

 twenty-five years it has been very generally destroyed by the use of 

 Paris green, and in more recent years also by London purple. These 

 poisons were first applied in dry form, being mixed with flour, 

 plaster, air slaked lime, and similar powders. The proportions of 

 the ingredients varied greatly, one part of the poison being added 

 to from one to fifty parts of the diluent. The mixture was then 

 dusted upon the plants by means of perforated boxes, or bags made 

 of coarse material. In recent years very effective machines have 

 been invented for the purpose of making uniform applications of 

 powder with great rapidity, and these have largely supplanted the 

 older devices. The powder is driven forcibly from the machines 

 by means of an air blast ; when applied in this manner it is well to 

 mix one part of poison with one to three parts of air-slaked lime. 

 The lime makes the powder visible as it leaves the machine, and it 

 also prevents injury from the poison ; for these reasons it is proba- 

 bly the best diluent to use. One and one-half pounds of these 

 arsenites per acre is sufficient for each application. 



The more popular methods of applying arsenites at present is to 

 mix them with one hundred and fifty to two hundred gallons of 

 water. An equal weight of quicklime should be added to the 

 mixtures, first slaking the lime in water. This prevents the caustic 

 action of the arsenites, and yet does not interfere with the machin- 

 ery. When poisons are applied in water with proper machinery, 

 rapid applications may be made at all hours of the day, and with 

 but little regard to the weather. 



Paris purple* is another form of arsenic which has been sold dur- 

 ing a number of years for the destruction of potato beetles. It 

 resembles London purple, but is of a deeper color and mixes with 



* Chemical aualysis of Paris purple siioweil it to contain 34.1 per cent, arsenic 

 trioxide, 40.7 per cent, of this being soluble in water. It is sold by Sykes »& 

 Street, 85 Water street, New York. 



