352 ENTOMOLOGY 



modifications in relation to the absence of light that are mentioned in 

 other parts of this book. 



Growth. In nature the effects of light on growth are bound up 

 with those of temperature. The temperature of the air varies with 

 light (insolation, or exposure to the sun's rays). Cloudy summer days 

 are cooler than sunny days. Cloudy winter days are warmer. (Shel- 

 ford.) Light affects the rate of growth, or more precisely, some wave 

 lengths are more effective than others. Beclard reared larvae of the 

 flesh-fly, Musca carniwra, from the eggs, under glass bells of different 

 colors. The largest larvse were found under violet or blue; the smallest 

 under green; the colors producing their effects in the following order: 

 violet, blue, red, yellow, white, green. Under violet the larvae were 

 three-quarters greater than under green. Green rays retarded growth, 

 as did also white light. (C. B. Davenport.) 



Activity. Sunshine, aside from temperatures, unless they are 

 extreme, has a stimulating effect on reproduction and other activities 

 in flies (Bishopp, Dove, Parman); and this is true probably for most 

 diurnal insects. On cloudy days the boll weevil and most other 

 insects as well are less active than on clear days, without regard to 

 temperature. 



Exposure to hot sunshine kills pupae of the boll worm, plum curculio 

 and other forms. This result is due primarily to heat with evaporation, 

 but possibly the ultra-violet rays also exert some influence. 



Sleep. Whatever the temperature may be, insects go to sleep when 

 night falls, and do so during the daytime if clouds diminish the sunlight 

 beyond a certain point which varies for different species. If it becomes 

 very cloudy, the mourning-cloak, Vanessa antiopa, seeks some crevice 

 and goes to sleep, but is quickly aroused, however, by returning sun- 

 shine. The sleep of insects doubtless has the same physiological 

 results as that of other animals. 



"A few species seem to choose protectively colored situations, and 

 others select sites which are in various ways protective. Some which 

 are solitary by day are gregarious at night, and some insects sleep with 

 all the regularity of a theoretical modern infant, while others of a more 

 unsystematic life snatch a wink when they can. " (P. Rau and N. Rau.) 



TEMPERATURE 



Temperature Limits. It goes without saying that the life-processes 

 and the activities of every animal or plant are confined within a certain 

 range of temperature, outside of which the organism cannot exist. 



