PAPERS ON ZOOLOGY 307 



may or may not be employed to combat outbreaks of 

 noxious insects with a reasonable assurance that the op- 

 eration will be successful. The present report relates 

 to some of the effects of different degrees of temperature 

 and different percentages of humidity upon the behavior 

 of an entomogenous fungus toward one of its insect hosts. 



The "green muscardine" of Metchnikoff\ Metarhizium 

 anisopliae, was chosen as the pathogenic agent in this 

 series of studies because of its cosmopolitan distribution, 

 because of its power to attack and destroy insects of 

 many widely separated taxonomic groups, and because 

 it has been employed in field operations with reputed 

 success by several former investigators of the subject. 

 For the insect host, pupae of the giant American silk 

 worm, Samia cecropia, were chosen, because they are 

 common and may easily be obtained in ample numbers, 

 because they are large and easily handled and observed, 

 because they are quiescent and more easily managed in 

 the exposure cages than the active stages of any insect 

 could possibly be, and finally, because they are avail- 

 able throughout the year if collected in the fall and kept 

 in cold storage. 



Constant temperatures of the various degrees indicated 

 were maintained in a battery of six incubators, and in 

 each incubator was provided a series of large dessicators, 

 the atmosphere within each of which was maintained at 

 a constant relative humidity by means of sulphuric acid 

 in appropriate dilutions. This method for maintaining 

 any desired degree of relative humidity is fully described 

 and tables of dilutions are given by X. E. Stevens, Phy- 

 topathology, vol. 6, 1916, pp. 428-432. Thus, a predeter- 

 mined series of humidity exposures could be made at the 

 temperature maintained in each incubator, affording a 

 temperature-humidity curve for each complete set of 

 tests. 



Spores both from pure cultures gro^\Ti on potato and 

 from infected cecropia pupae were employed in the course 

 of the work, and in each test two lots of pupae were used, 

 which were treated with these spores in two different 

 ways. The pupae in one of these t^'o series were simply 



