eyes increased rapidly during the first few minutes in darkness then more slowly until it 

 reached a maximum sensitivity in bees held for 25 to 30 minutes in darkness. With no 

 further increase in sensitivity the process of dark-adaptation was said to be complete. 



Predisposition and response to light . Numerous studies have been made on the 

 photosensitivity of insects that had been predisposed to certain conditions. Honey bees 

 were trained (17) to come to food in a trough illuminated at 3650 angstroms (A.). Food 

 was removed and the entire .spectrum was projected on -white paper. Bees congregated 

 for the most part on the area subjected to 3650 A. even in the absence of food. 



Von Frisch (12) in studies to determine whether chroma vision existed in the honey 

 bees conditioned them to given colors. He then placed squares of this color on a checker- 

 board of grays. The bees could pick given colors regardless of their position on the 

 checkerboard, but could not distinguish red. Those conditioned to yellow confused yellow, 

 orange, and yellow green; those that were conditioned to blue confused blue, violet and 

 purple. 



A similar sort of preconditioning was performed in studying color discrimination 

 in droneflies (16). 



Mosquito larvae of the genus Culex and Aedes indicated the influence of diet on 

 phototropism (20). Larvae fed on a mixed diet of pond organisms were positively photo- 

 tropic. When fed a pure ciliate diet, they changed from a positive to negatively photo- 

 tropic response in two days. 



Age of insects and spectral sensitivity. Insects as a class respond to electromagnetic 

 radiation in the approximate range of2537to7000 A., from the ultraviolet to the infrared. 

 It is generally agreed that most insects show greatest sensitivity to the near ultraviolet 

 region, a gradual decline to the blue, an increase to a secondary peak in the blue-blue 

 green region, and the least attraction to the longer wavelengths. The intensity of light 

 plays an important role. It was shown (23) that at an introductory intensity of 100, peak 

 response for most of 29 species took place at 4700-5280 A., but at an introductory in- 

 tensity of 3 the peak response was at 3650-3663 A. This phenomenon confirms the belief 

 that a "Purkenji shift" occurs in insects (10). This is a shift of overall sensitivity to 

 shorter wavelengths under low illumination. 



The spectral sensitivity of the larvae of 16 species of insects was determined (23). 

 Nine were most sensitive to 3650 A.; the balance to 4920-5150 A. Unfortunately, in only 

 1 species, the Colorado potato beetle, was the sensitivity determined for both larva and 

 adult. Both stages showed maximum sensitivity to 3650 A. with a secondary peak at 4920 A. 

 Only 1 reference (23) was found that indicated the influence of age to photosensitivity. 

 Drosophila adults 3 to 4 days old were less interested in light than individuals 6 to 8 days 

 old. Those in the most responsive stages were highly sensitive to small amounts of ultra- 

 violet radiation. 



The foregoing remarks are chiefly of academic interest, but serve to illustrate the 

 diversity in insect phototropism. There is no doubt but that a greater fund of basic in- 

 formation -would lead to a more logical pursuit of practical problems. The remarks that 

 follow relate only indirectly to the physiological development of insects to photosensitiv- 

 ity. They are reports on observations made almost exclusively in the field. 



Meteorological influence on insect activity, not on photosensitivity . It is reported 

 that most Lepidoptera are definitely inhibited at temperatures below 60° F. and are the 

 most active at 65° to 70° F. (6). Codling moths in New Mexico (8) were inhibited in flight 

 at temperatures above 80° or below 60° F. When temperatures dropped below 58° to 

 60° F., flight and catches of corn borer moths in light traps decreased rapidly even on 

 nights when maximum flights were expected (9). The influence of wind on flight activities 

 has been recorded. Corn borer moths (22) flew above corn tops when the night was still 

 but flew below the tops when night -was breezy and blacklight traps caught moths accord- 

 ingly. The effect of temperature and wind action on pink bollworm moths was observed (13). 



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