NO. 10 TROPISMS OF LEPIDOPTERA — McINDOO 39 



with another brush wet with sugar sohition the proboscis is quickly- 

 extended. These hairs are so sensitive that a single one, when touched, 

 may produce the response. According to the accepted definition of 

 taste, these hairs are true taste organs provided the sugar solution 

 must actually touch them; if only a close proximity is required, then 

 the sense of smell is involved. When asked this question, Minnich 

 was not sure that he had totally eliminated smell. If these hairs are 

 true taste organs, the present writer cannot understand how an aque- 

 ous solution can pass instantaneously through their walls in order to 

 stimulate the nerves inside. 



III. AUDIRECEPTORS 



The common belief that insects can hear is based on three facts : 

 (i) Many of the experimental results obtained indicate that they 

 can perceive sound stimuli, although perhaps they do not hear as we 

 do; (2) many have special sound-producing organs; and (3) many 

 have so-called auditory organs. 



The first report on the auditory sense of Lepidoptera was probably 

 made in 1876. Since that date much has been published, but critics 

 are still inclined to doubt whether any insect can really hear. 

 Turner (86) and Turner and Schwarz (87) in 1914 produced good 

 experimental evidence to show that Catocala and giant silkworm moths 

 really hear. They used an adjustable organ pipe, an adjustable pitch 

 pipe, and a Galton whistle. Their field experiments demonstrated that 

 most of the moths tested can hear high-pitched notes, but usually 

 low-pitched ones did not produce responses. They believe that re- 

 sponses of moths to sounds are expressions of emotion and that a 

 response depends upon whether the sound has a life significance to the 

 insect tested. 



For many years it has been known that both adult and larval Lepi- 

 doptera are able to produce sounds and some of the sound-producing 

 organs have been described. For example, the death's-head moths 

 (Acherontia) make shrill chirping sounds, probably by forcing air 

 through certain parts of the anatomy. Their larvae produce " crack- 

 ling " notes. A hissing noise is made by several species of Vanessa and 

 more pronounced sounds are produced by other Lepidoptera. Stridu- 

 lating organs on the wings have been described by several, including 

 Hampson (28) and Jordan (35). In certain Agaristidae and Geo- 

 metridae the sound is made by pressing the tarsi against the ribbed 

 areas on the wings. This subject is reviewed by Schroder (80, pp. 61- 

 74) and Hering (32, pp. 190-193). 



