1919] Mclndoo: Olfactory Sense 83 



SUMMARY. 



To determine whether lepidopterous larvae respond to chem- 

 ical stimuli, tent caterpillars, fall webworms, tussock-moth 

 larvae, army worms and larvae of Papilio polyxenes were tested 

 by using the following sources of odors: Oils of peppermint, 

 thyme and wintergreen, dried leaves of pennyroyal and spear- 

 mint, wild cherry-tree leaves, fresh grass, old honey and comb, 

 and the protruded thoracic glands of the above Papilio larvae. 

 The larvae usually responded to the exhalations from these sub- 

 stances, but the average reaction times obtained seemed to 

 depend more on the degree of sluggishness of the larvae than on 

 their sensitiveness to odors. 



Organs, called olfactory pores by the writer, but known as 

 punctures to systematists, were found widely distribute.d on the 

 head capsule, head appendages, legs, dorsal surfaces of the 

 prothorax and last abdominal segment, and on the anal prolegs. 

 It is believed that a few of those on the head and all of those 

 found on the legs and abdomen are here reported for the first 

 time. Their internal structure is like that of those in adult 

 insects and coleopterous larvae, and consequently are well 

 adapted to receive chemical stimuli, because their sensory 

 fibers running from the sense cells pass into the minute pores 

 or punctures and seem to come in direct contact with the 

 external air. No experiments, however, were performed to 

 determine their function. 



Verschaffelt determined experimentally that cabbage-butter- 

 fly larvae are attracted by the various mustard oils contained in 

 the host plants, and this explains why these larv« refuse plants 

 not containing such oils ; he also thinks that the larvae smell the 

 odors from the mustard oils before they begin to eat the food. 

 If we knew more about the chemotaxis of insects, we might be 

 able to devise practical methods for the control of certain 

 insects, as by trap baits, etc. 



