266 JOURNAL OF ECONOMIC ENTOMOLOGY [VoL 1 



dicates that a broad field for chemical, entomological and physio- 

 logical research is waiting for explorers. 



Everyone who sprays is aware how variable are the results he ob- 

 tains at different times; how one treatment may be very successful 

 while another, under apparenth' similar conditions, may prove much 

 less satisfactory. Some writers advise spraying on warm, cloudy 

 days ; others on bright days to obtain the best results. The addition 

 of one or two pounds of lime to each pound of Paris Green to prevent 

 burning the foliage is generally urged; yet, even then, injury some- 

 times follows, and the only explanation generally offered seems to be 

 that the materials were not sufficiently well mixed. 



It is generally claimed that injury to foliage is due to the presence 

 of free (uneombined) arsenic in the spray, l)ut it is interesting to note 

 that even this has not been conclusively proven. And when the na- 

 ture of the action of the poison on the insect is questioned, the an- 

 swer seems to have been drawn entirely from human toxicology rather 

 than from a study of the poisoned insects themselves, while differences 

 in the ease with which different pests are killed by poisons have been 

 explained as due to varying powers of elimination of the poisons 

 from their bodies, — only a guess, though one which may prove to be 

 correct. 



Even the chemical aspect of the insecticides has its uncertainties. 

 Dictionaries of solubility state that copper arsenite is insoluble in 

 Avater, whereas everyone who has used this substance as a spray knows 

 that it is necessary to add lime to prevent burning the foliage. It 

 would seem then, either that such statements as to solubility are very- 

 loose in their nature, or that the burning is due to some of the im- 

 purities always present in commercial articles. Which is the truth? 

 What are the impurities and what parts may they play when used as 

 sprays ? These and many other questions must be settled by the 

 chemist and entomologist working together. . 



Weather conditions have already been mentioned. How far do 

 these affect or modify results when other factors remain fixed? Is it 

 sunlight, temperature, humidity or all these and perhaps other con- 

 ditions in addition which are involved? The meteorologist must 

 also contribute his share toward the solution of spraying problems. 



At the present time there are too few data of experiments made 

 under conditions known with exactness; with materials of fixed and 

 known composition ; and with careful studies of the results, to enable 

 us to draw safe conclusions on this subject. INIany factors are in- 

 volved and these must each be studied separately in their changes 

 while the others remain fixed, thus involving long series of experi- 



