C. E. Abbott.
The Reaction of Datana Larvae to Sounds.
Psyche 34:129-133, 1927.

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19271 The Reaction of Datana Larva to Sounds 129 THE REACTION OF DATANA LARVA3 TO SOUNDS. BY CYRIL E. ABBOTT,
Zoological Laboratories, Johns Hopkins University. A considerable amount of discussion has been devoted to the possibility of the presence of an auditory sense in insects. Unfortunately, much of this discussion has been purely theo- retical. At one time it was generally supposed that all or most insects could hear.
This argument was based upon two facts:
the possession, by insects, of sensory organs which have a struc- ture indicating a possible auditory function, and the insect production of sounds. For what other purpose, it was argued, can stridulating organs be used, if not for that of impressing other insects?
Fabre fired two mortars in close proximity to a number of Cicadse without affecting their songs. He concludes, "If any one were to tell me that the Cicada strum on their noisy ins- truments without giving a thought to the sound produced and for the sheer pleasure of feeling themselves alive, just as we rub our hands in a moment of satisfaction, I should not be greatly shocked." Lutz (1926) is of the same opinion. He writes: it
When we can explain the purpose of a man's snoring or the rattling of a Ford car, we may know why this beetle grub rasps. Having slept with a man that snored and having driven a Ford, I believe that the sounds in question are unintentional and quite incidental to the structure of the man and of the machine. May not the same be true of the beetle grub?" In spite of such incomplete considerations of the subject, there is evidence that certain insects have an auditary sense. Radl (1905), arguing in part from structure, and in part from experiment, concludes that insects have auditory powers of a primitive and limited kind.
In 1914 Turner and Shwarz tested the auditory powers of various Catacola moths, and found that from 80 to 100 percent of the insects gave positive responses to notes of the pitches C,4 A,4 and B4 from a Galton whistle. In the same year Turner



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130 Psyche [April
conducted a number of similar experiments, using the adults of the large Saturnidae as subjects. A majority of the insects gave positive responses to a wide range of notes sounded on various wind instruments.
In 1925, Kroning tested the auditory sense of bees with a siren. His extensive experiments lead him to the conclusion that, "die Bienen konnten keine Tone wahrend des Fliegens horen, wohl aber in Marsch oder wahrend des Sitzens." Minnich (1925) brings forth positive evidence in support of the presence of an auditory sense in the larvae of Vanessa antiopa. His experiments were extensive and complete. He found that these larvae, when stimulated by sounds, quickly elevated the anterior third of the body. Minnich was very careful to eliminate other possible sources of stimulation. The larvae of all instars responded; even headless individuals, and parts of the body were capable of response. Minnich also removed the spines; in other cases he loaded them with water droplets or dry flour. Larvae so treated failed to respond to sounds. The larvae were tested with a wide range of notes. Mature larvae responded to notes between C " (1024 vibrations) and C3 (32 vibrations.) The experiments of Minnich suggested to me the possibility of similar reactions in Datana larvae. These insects are the caterpillars of certain moths. They feed in groups, and give very definite responses to various external stimuli. Air currents, sudden jars, and certain sounds cause each larva to elevate t,he anterior and posterior thirds of its body; contact with the sub- stratum is maintained by means of the four middle pairs of prolegs. If the stimuli are continued, the insects may throw their heads from side to side.
The larvae of D. perspicua feed on sumac. Just prior to
metamorphosis they measure about two inches in length by one- fourth of an inch in width. Their general color is black, but they are marked by several longitudinal yellow stripes. The body is covered with long grayish hairs, so sparsely that the surface of the body is easily visible, but plentiful enough to constitute a



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19271 The Reaction of Datana Larvce to Sounds 131 marked anatomical feature. The larvse of D. ministra feed on various species of Cratsegus. They resemble the larvae of D. perspicua very closely; the most striking difference is due to the orange color of tohe prothoracic segment. The responses of the two species are similar, but those of D. ministra are not as marked as those of D. perspicua.
Preliminary tests demonstrated that these larvae give mark- . ed responses to only two notes: middle C (512 vibrations) and F sharp above middle C (728 vibrations). The responses were very distinct. The instrument used in making the tests was a closed pipe with a movable plunger. Eleven larvse were used in each test. The number was purely arbitrary. They were taken from a large cage in which they were kept, and placed on a ver- tical stick. The tests were made after the caterpillars started to creep. In every case, efforts were made to protect the insects from air blasts from the pipe.
In the critical series of tests, normal larvse of D. perspicua were used only as controls, but a complete set of tests was made with normal larvae of D. ministra. .
Attention was chiefly directed toward the role of the hairs in the detection of sounds. The methods employed were similar to those used by Minnich in 1925; the hairs were "loaded" with water or shellac. The liquids were sprayed on to the hairs with a nasal "atomizer." As the water had a tendency to run off, it had to be frequently renewed. The shellac was the commercial orange product diluted with an equal volume of ethyl alcohol. Its value lay in its stability; the alcohol soon evaporated, leaving . the droplets of shellac fixed on the hairs. These methods of treatment did not seriously injure nor inconvenience the larvae. Some specimens of D. perspicua were bathed with a 2 percent solution of procain. Although this inhibited responses, it was more or less injurious, and several of the insects so treated sub- sequently died.
Ten trials were made with each group of larvae; five for each set of vibrations. Four specimens of D. perspicua were tested after removing the hairs from their bodies by clipping. Normal in- sects were also tested with a piano and a mandolin. The results of the experiments are tabulated as follows:



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Psyche
Table I Datana perspicua
Vibration Water Shellac
512
- -
728 slight -
512
-
728
- -
512
- -
728
- -
512
-
. 728
- -
512 -
-
728
- slight
Control + +
Vibration
512
728
5 12
728
512
728
512
728
512
728
Table I1 Datana ministra.
Normal Water
+ .
-
+
+
-
+
-
+
-
+
-
+
-
+
-
+
-
+
-
Procain
-
slight
-
Shellac
The results of these experiments are startling. In only three were even slight responses elicited after treatment. That the responses are actually due to the sound is evident from the fol- lowing facts: the response of normal larvae is given when the in- sects are protected from all air currents, it can be elicited when the larvse are several feet away from the source of the sound, it was given to any one of three different musical instruments, and



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1927 The Reaction of Datana Larvce to Sounds 133 finally it was elicited when all possibility of vibrations of the substratum were eliminated.
These facts are supported by the results obtained when the hairs were loaded or removed, or when the body surface was ansesthitized.
What is the significance of this peculiar sense? The larvee give marked responses to only two notes, which, even if they were frequent under natural conditions (which t,hey certainly are not), could hardly be considered of importance to the caterpillars. They are, therefore, not adaptive. It is probable that we are here in the presence of a "secondary" sense, developed as a result of the adaptation of certain organs to more significant stimuli.
Literature.
Fabre, H.
1919. The Life of the Grasshopper. (Trans. from Sou- venirs Entomologiques by A. Teixeira de Mattos), New York. p. 78.
Kroning, F.
1925.
Uber die Dressur der Biene auf Tone. Biol. Zen- tralbl. 45, p. 496.
Lutz, F.
1926.
Insect Sounds. Nat. Hist. Mag. 26, No. 2.) p. 206. Minnich, D. E.
1925. The Reactions of the Larvse of Vanessa antiopa Linn. to Sounds. Jour. Exper. 2001. 42, No. 4. Radl, E.
1905.
Ueber das Gehor der Insecten. Biol. Centralbl. 25. Turner, C. H.
1914. An Experimental Study of the Auditory Powers of the Great Silkworm Moths. Biol. Bull. 27) No. 6. Turner, C. B. and E. Shwarz
1914. Auditory Powers of the Catocala Moths; an Ex- perimental Field Stxdy. Biol. Bull. 27.




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