REACTIONS TO LIGHT 167 



had been demonstrated. The opinion is advanced that a 

 physiological effect on the insects is involved and that a reduction 

 in the efficiency of the trap when the moon is shining is not the 

 explanation. Further experiments to test this conclusion are 

 being carried out by using traps not dependent upon light as the 

 source of their attracting power. 



The use of light traps for determining the population density 

 of the Rice-Borer by Harukawa, Takato and Kumashiro (1935) 

 has not proved reliable over a period of years. The larvae may 

 become very abundant even when the moth population, as 

 determined by light traps, is not very large or, in other words, 

 the larval population is not proportional to that of the number 

 of moths captured. The light trap captures, therefore, are not a 

 trustworthy index of the abundance of larvae to be expected in the 

 next generation. The population density can be best determined 

 by collecting injured rice haulms and by direct counting of the 

 larvae found. 



The reactions of insects to colour {vide also p. 113), apart from 

 questions of light intensity, have certain practical applications, and 

 merit more extended study than has been accorded to them. 

 Nuttall showed many years ago that mosquitoes have a marked 

 tendency to congregate and rest on a dark blue surface — a fact 

 which has led to certain practical developments. Lloyd (1921) 

 demonstrated that the white -fly Asterochiton vapor arioruin is 

 powerfully attracted to a yellow colour, while Folsom and Bondy 

 (1930) found that applications of calcium arsenate dust to cotton 

 plants are often followed by heavy infestations of Aphis gossypii. 

 One of the factors operating in this case was found to be due to 

 the positive phototropic reaction of the winged aphides to the 

 white deposit of calcium arsenate on the plants. Other white 

 dusts, such as calcium carbonate, starch or flours, were also found 

 to induce a similar response on the part of that insect. In tropical 

 Africa the method of trapping tsetse-flies, on tanglefoot screens 

 attached to moving automobiles, ajDpears to offer room for 

 exploration with respect to the colour surfaces most attractive 

 to those species. 



Concluding Remarks. Reactions to chemical stimuH, and to 



