April, '14] SHELFORD: MEASURE OF EVAPORATION 229 



suspecting that something unusual might be going on I had one of my 

 students make collections and from these he bred out two species of 

 parasites in proportions of perhaps 98 per cent and 2 per cent. In 

 these collections about 80 per cent of the scales were parasitized. 

 The parasites which emerged in such large numbers were sent to 

 Doctor Howard who reported that they were a new species and the 

 original description was accordingly published in the Annals of the 

 Entomological Society of America for March, 1913, by Mr. D. G. 

 Tower. As a result of the observations which have been made, we 

 find that during the past fall in some localities 90 per cent of the 

 scales are parasitized. It seems to me that we are in a position of the 

 bacteriologist who is able to furnish pure cultures and I am ready to 

 make a proposal in spite of what Doctor Howard has said, to the effect 

 that we will send a few parasitized twigs to any entomologist who is 

 interested in the matter. I agree with Doctor Wheeler that if 90 per 

 cent of the scales are parasitized, the remaining 10 per cent will, 

 nevertheless, furnish an abundant supply for reproduction. If the 

 percentage of parasitism increases as it has in the past two years the 

 results ought to be helpful. Our best results have been secured from 

 collections made from unsprayed trees such as Cornus and Salix. 



Mr. a. C. Lewis: I have only seen one or two cases in Georgia 

 where the fungus disease did any particular good in destroying the 

 San Jose scale. I do not think it can be depended upon as remedy in 

 this state. 



President P. J. Parrott: The next paper will be presented by 

 Mr. V. E. Shelford. 



THE IMPORTANCE OF THE MEASURE OF EVAPORATION 

 IN ECONOMIC STUDIES OF INSECTS 



By Victor E. Shelford 



The economic importance of any environmental factor is deter- 

 mined by the character of its influence upon organisms of economic 

 importance. Environmental factors influence organisms chiefly in 

 one of three ways: (a) by stimulating migrating animals and causing 

 them to turn back, (b) by producing death, (c) by modifying rate of 

 metabolism, fecundity, length of life, size, etc. Recently attention 

 of entomologists has turned to the study of optimum conditions for 

 insect growth and rate of insect metabolism (Hennings^ Sanderson^, 

 Headlee^). In these studies the chief criterion of increased meta- 



I Zeit Land und Forst-Wirt, 5 jrg (a) p. 68. 

 = Jour. Econ. Ent., Ill, p. 113. 

 3 Science, N. S., XXXVI, p. 310. 



