Cyril E. Abbott.
The Effect of Temperature and Relative Humidity upon the Olfactory Responses of Blowflies.
Psyche 39(4):145-149, 1932.

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19321
The Olfactory Responses of Blowflies
THE EFFECT OF TEMPERATURE AND RELATIVE
HUMIDITY UPON THE OLFACTORY RESPONSES
OF BLOWFLIES
Morgan Park, 111.
Introduction
It appears that almost no effort has been made to deter- mine the possible conditioning of insect olfaction by other external factors. This may be due to the fact that studies in the relation of these factors to insect metabolism are comparatively recent. In 1917 Headlee discovered that at- mospheric moisture, through its relation to the water op- timum of the insect body, directly affects development. In the same year Hamilton found that above 20å C soil insects are especially sensitive to evaporation. Shelford (1913) observed that insects resisted drying more effectively that most other animals. Beattie (1928) has made some inter- esting experiments with Calliphora erythrocephala. She
finds that a relative humidity of 70 is optimum for the spe- cies, and that saturated or dry air lowers the thermal death point. Miller (1930) finds that at 37.5O C the percentage of surviving adult Mexican bean beetles, irrespective of hu- midity, is high.
At 42.5O C the percentage is low at all
humidities, while at temperatures between the extremes, the greatest 'percent of survival is at a relative humidity of 73. Marchand (1920) observes that Blatta, Chionea and various species of mosquitoes orient to heat. According to Herter (1923) Formica mfa distinguishes temperature changes as low as VA,å C. Miller and Gan were able to make Cremastogaster lineolata orient to radiant heat. Lodge (1918) finds that Musca domestics has its feeding reactions affected by changes in temperature and humidity.



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146 Psyche [ December
The following study was suggested by Kennedy's (1927) statement that the olfactory powers of certain Hymenop- tera appear to vary with relative humidity. Under normal conditions, adults of Lucilia sericata, Meig. react to ethyl butyrate by an extension of the proboscis and regurgitation of fluid (Fig. 1). This is a definite feeding response to ol- factory stimulation. The problem was to determine to what extent this response is dependent upon temperature and relative humidity.
Fig. 1.
Extension of proboscis and regurgitation by Lucilia sericata.
Maderials and Methods
Adult flies were kept in small cages and fed a solution of cane sugar and what juices they could obtain from hog's liver. The latter was replaced every alternate day, and any eggs removed to flower pots about two-thirds full of sand. These containers were covered with muslin. The maggots pupated in the sand and as soon as adult flies began to emerge in a given container, the latter was transferred to one of the cages.
Flies were tested individually and discarded after each test. The insect was placed in'a chamber consisting of a test tube fitted with a rubber stopper having two inlet tubes. During the test, this tube was kept in a constant tempera- ture bath composed of an aquarium fitted with two Lolag heaters, a thermostat, a stirring device, and two U-tubes which served to equalize the temperature of the air drawn into the fly chamber. One of these tubes was connected with the "check" apparatus; the other with the "test" ap- paratus. When properly adjusted, the temperature of the



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19321 The Olfactory Responses of Blowflies 147 tank never varied more than 1/5O C. Each of the units used for the control of humidity consisted of two bottles ar- ranged so that air was drawn through solutions they con- tained; in addition, the "test" set had a vessel containing ethyl butyrate shunted between these bottles and the U- tube. This vessel was held at a constant temperature of 30å C. in all tests.
Relative humidity was controlled by chemicals. A con-
centrated solution of a given compound gives the air with which it comes in contact a definite relative humidity. Four were used :
Chemical Relative humidity
H20 98-100
NaCl 73
NaOH 30
NzSO. 0-4
The general method was to change the humidity, the temperature being constant. The tests at the four humidi- ties were then repeated for another temperature. Three temperatures were used: 20' C., 30' C., and 40' C. Flies were collected in the afternoon and were kept with- out food for five hours.
They had free access to water.
Sixty-four flies were used in each test. The method of
procedure was as follow,^ : a fly was secured on the end of a galvanized iron wire by wrapping its wings and the end of the wire with adhesive tape. The opposite end of the wire was fixed in the lower surface of the rubber stopper of the test chamber.
This last, containing the stopper with the attached fly and tubes was placed in the constant tempera- ture bath for one minute. One inlet tube was attached, by means of a rubber tube, to the 4'check'7 apparatus. The
other inlet tube was similarly attached to a water-pump. The fly was observed for thirty seconds. If it did not re- spond (which was generally the case) the tube attached to the "check" apparatus was transferred to the "test" ap- paratus. Again the fly was observed for thirty seconds. If it extended the proboscis within this time, it was con- sidered "positive." Sexes were used in about equal num- bers. Percentage of response was based upon the number



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Psyche
[ December
of insects giving a positive reaction at a definite tempera- ture and humidity.
Results
The results of the foregoing tests are embodied in the fol- lowing graph (Fig. 2). Neither at 20å C. nor at 40å C. was the percentage of response very high. The highest (57%) took place at 20å C. in a saturated atmosphere. At 30' C. there was a rise in percentage of response almost directly proportional to the increase in humidity, until the latter reached 73%, after which it fell slightly. At 30å C. and a a
10
<s
0-
30 73 100
Relative Humiilily
Fig. 2.
Olfactory responses of blow-flies.
humidity of 73% the percent of response was 89; at a hu- midity of 100% it was 76. There was no indication of sex differences in these responses. The fact that there were practically no responses to the "check" indicates that it was really the vapor of ethyl butyrate and not air currents that brought about the responses.
General Conclusions
Several months of breeding and general observations in- dicate that the most favorable temperature for the meta- bolism of L. sericata is about 30'
C. In the light of this
fact, the discrepancies between the behavior of flies tested at that temperature and those tested at other temperature ranges can be easily understood. Apparently it is only at



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19321 The Olfactory Responses of Blowflies 149 the temperature of metabolic optimum that humidity has much effect on their olfactory responses. At that tempera- ture, the optimum for humidity is 73%.
It is a pleasure to thank Dr. C. H. Kennedy, Dr. W. M. Barrows, and Dr. D. F. Miller for many suggestions, ma- terials, and aid in carrying this problem to a successful conclusion.
LITERATURE CITED
Beattie, M. F. V. 1928. B~ul. Ent. Research, 18, 397-403 Hamilton, C. C. 1917. Biol. Bul., 32, 159-177 Headlee, T. J. 1917. Jour. Econ. Ent., 10, 31-38 Herter, K. 1923. Biol. Zentbl., 43, 282-285 Kennedy, C. H. 1927. Ann. Ent. Soc. Amer., 20, 87-106 Lodge, Olive C. 1918. Bul. Ent. Research, 9, 141-151 Marchand, W. 1920. Ent. News, 31, 159-161 Miller, D. F. and M. Gan 1926. Jour. Compar. Psychol. Miller, D. F. 1930. Jour. Econ. Ent., 23, 945-955 Shelford, V. E. 1913. Biol. Bul., 25, 79-120



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