NO. lO TROPISMS OF LEPIDOPTERA — McINDOO II 



were kept in battery jars and drinking glasses, and an accurate record 

 of the age, size, color, and behavior of the infesting larvae was 

 recorded. The instars were determined by use of Dyar's (14) method 

 of head measurements, the live larvae being rendered inactive by 

 laying them upon a piece of ice on the microscope stage. Temperature 

 and humidity records were obtained from centigrade thermometers 

 and a h}grothermograph. Notes pertaining to the date, time of day, 

 character of sky and wind, degree of brightness of sunshine, and 

 rainfall were recorded, but unfortunately it was difficult and some- 

 times impossible to correlate climatic conditions with the tropic re- 

 sponses obtained. For this type of work more refined methods and 

 apparatus are badly needed. 



Since it was not possible to carry on phototactic tests among the 

 trees in orchards in the natural environment of these insects, the 

 next best condition was to use daylight in the laboratory. Daylight, 

 however, was unsatisfactory because the intensity varied daily and 

 even from hour to hour, so that comparative quantitative results 

 were impossible. Artificial light with a lOO-watt " daylite " bulb was 

 tried. The larvae usually responded to it only after being touched 

 and then very feebly. For these experiments a simple and quick 

 method for determining daylight intensities was badly needed, but 

 none seemed available. 



Relative to ecological photometry and means of measuring light, 

 Klugli (39) presents a critical review of the entire subject and then 

 describes a new instrument, called an ecological photometer. There 

 are already three kinds of instruments of high precision for measuring 

 radiation. Two of them, the pyrheliometer and spectrobolometer, are 

 used by the astrophysicist and the third, the spectrophotometer, is 

 employed by the physicist. The new instrument is said to meet the 

 needs of the ecologist, but in order to operate it one should be con- 

 siderably experienced in photography. Using the new instrument 

 Klugh obtained very interesting results. As an example to show the 

 great variations in daylight intensity, he selected an open habitat on a 

 bright clear day, July 26. Letting the intensity at noon equal 100 per 

 cent, he then determined the following percentages of intensities : At 

 9 a. m., 90 per cent ; at 5 p. m., 83 per cent ; at 6 p. m., 66 per cent ; 

 and at 7.45 p. m., 5.2 per cent. On another bright sunshiny day he 

 found the intensity to be only 2 per cent in a woods while in the open 

 it was 100 per cent, but on a cloudy day it was 10 per cent in the 

 same woods as compared to 100 per cent in the open. The intensities 

 on clear and cloudy days vary greatly. Filmy clouds over the sun 



