NO. lO TROPISMS OF LEPIDOPTERA — McINDOO 23 



The following discussions pertain to what is generally described 

 under sense organs and the senses, but no attempt is made to give 

 all phases of this subject, and most of the information pertains to 

 Lepidoptera. 



I. PHOTORECEPTORS 



The photoreceptors are the compound eyes and ocelli and there is 

 no difficulty in connecting the compound eyes of adult moths and 

 butterflies and the ocelli of their larvae with the phototactic responses 

 obtained experimentally. The usual number of ocelli on an adult insect 

 is three, but the sexes of the codling moth have only two each. Judging 

 from sections through the eyes of both adult and larva of this moth, 

 the photoreceptors seem to be normally developed, but since so much 

 work already has been done on the morphology of insect eyes no 

 special study was made on this subject. The reader is referred to the 

 reviews by Schroder (80), Snodgrass (81), and Hering (32). 



So far as is known to the writer the only new idea on this subject 

 is advanced by Lammert (40), who believes that lepidopterous larvae 

 have two kinds of photoreceptors — the ocelli and others (probably 

 pigment specks) in the body integument. Therefore, he believes that 

 these larvae have a skin sensitive to light, which might be compared 

 to that in the earthworm and other animals having photopigment 

 widely distributed in the body wall. 



The results obtained by Durken (13) bear indirectly on the subject 

 of body pigment used to direct the movements of larvae. He experi- 

 mented five years to determine the efifects of colored lights on the 

 developing stages of the cabbage butterfly. Glass panes of vivaria 

 were painted white and the efifect of reflected light from green food- 

 stuffs on the caterpillars was observed. Darkness produced some 

 reduction of black pigment, while orange or red light produced much 

 reduction of black and white pigments. Blue light caused a slight 

 shifting in the direction of weaker pigmentation. Reaction to light 

 occurred immediately before pupation. There was no effect previous 

 to that time on the pigmentation of pupae. Pigmentation of imagoes 

 was entirely unafifected by darkness or light, being absolutely inde- 

 pendent of that of the pupae. 



In regard to whether sight or smell plays the greater role among 

 flower-visiting insects, Clements and Long (5) present the best recent 

 reviews of the literature. They conclude that phototaxis is more 

 important than chemotaxis. Odors attract from a distance while sight 

 attracts from nearby. Form and size of objects play a lesser part in 

 attraction. 



