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JUL 7 1919 -u^ 

 ANNALS X^:^Mjh^ 



OF 



The Entomological Society of America 



Volume XII JUNE. 19 19 Number 2 



THE OLFACTORY SENSE OF LEPIDOPTEROUS LARViE. 



N. E. McIndoo, Ph. D., 



Insect Physiologist, Deciduous Fruit Insect Investigations, 

 Bureau of Entomology, Washington, D. C. 



INTRODUCTION. 



A thorough investigation of the above subject will undoubt- 

 edly throw some light upon how plants attract insects, because 

 as yet no one has shown experimentally that lepidopterous 

 larvae can smell and the olfactory organs have never been 

 described. Whenever it is proved that insect larvae respond to 

 chemical stimuli, and whenever organs suitable for the reception 

 of these stimuli have been found, then we can intelligently ask 

 why do the cotton caterpillar (Alabama argillacea Hiibr.) and 

 cotton boll weevil (Anthoiiomns grandis Boh.) feed exclusively 

 on the cotton plant?; or why does the silkworm (Bombyx mori 

 L.) feed almost exclusively on mulberry-tree leaves?. Many 

 more similar examples could be given by any entomologist, but 

 why is it that some larvae are very selective in regard to their 

 food while others show little or no preference between members 

 of a large list of plants. Also, how does a female lepidopteron 

 distinguish the best or only suitable host plant for her progeny 

 so that she can deposit her eggs on this particular plant? The 

 only plausible answer for all of these questions is to suppose 

 that plants, as well as animals, emit odors, and that insects in 

 searching for food,, either for themselves or for their young 

 progeny, are guided by the odors emitted by the plants. In 

 order that the odors of plants may differ, it may also be assumed 

 that the various chemical constituents of plants emit particular 

 odors and that the odor emitted from a plant may be a com- 

 bination of all the odors from the various constituents, or pos- 

 sibly one odor might be so strong that it masks all the others. 



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