STUDIES ON INSECT METAMORPHOSIS.

Transcription

1 STUDIES ON INSECT METAMORPHOSIS. IV. EFFECT OF CARBON DIOXIDE.* BY HEM SINGH-PRUTHI, Ph.D. {From the Zoological Laboratory, Cambridge.) THE problem of how the apparently healthy organs of the larva of the holometabolic insects, at the height of their maximum growth, become disintegrated and the rudiments of the imaginal structures, dormant up to this time, begin proliferating and developing into functional organs, is a very interesting one and has attracted the attention of numerous physiologists and entomologists. Bataillon (893), as a result of his elaborate researches, established that there was an accumulation of CO S in the blood and body cavity of metamorphosing silkworms. Previously, he (89) had observed the same state of things in the Anura. Bert (885) had previously noticed respiratory abnormalities in silkworms ready to pupate. On the basis of these observations Bataillon advanced the theory that in the metamorphosis of insects the first event is the destruction of larval organs, i.e., histolysis, and that this is brought about by the suffocation effect of the accumulated CO* Terre (900) endorsed this view, while Perez (903) and Mercier (907) were sceptical about it. In order to test the asphyxia theory of Bataillon I carried out the following experiments : I. 220 larvae of the Blowfly {Callophora erythrosephala), which had almost ceased feeding and were ready to pupate, were divided into two lots of 0 individuals each. One series was put in a jar (6" high and 7.5" in circumference) into which 500 c.c. of CO S (at N.T.P.) were introduced, after which the mouth of the jar was at once closed; thus the larvae were practically in an atmosphere of almost pure carbon dioxide. The other series was put in a jar of the same capacity as the above, but containing no COj and with its mouth uncovered this served as control. Received April 7th,

2 Hem Singh-Pruthi The above experiment was started on 4/2/25 at 0 a.m. As will appear from Table I., on the 6th, while there were 9 pupae in the control, there were only 5 in the CO, jar. On the 7th (0 a.m.) there were 95 pupae in the former, and 3 only in the latter. By the evening of the same date all the individuals of the control series completed pupation, while only 5 of the COj lot had changed. During the next six days only 6 more individuals of this series metamorphosed. On the 24th the lid of the CO a jar was removed for twenty minutes; many larvae were found clinging to the lid near its TABLE I. Date of Total Number of Pupse formed to Date. Suffocated Series. Remarks. Started on M/2/ No. of individuals - subjected to suffocation: no Feb. 6, 4 p.m., 7, 0 a.m. 7, 6 pjn, 8, 0 a.m., 9, > *>n 3O >, 24,, 25,, 26,, 37,, 38, Mar. 3,,, 6, C died 9 95 no Lid of the CO, jar removed for 30 rininutes. Lid of the CO, jar removed permanently. margins. After this dilution of. CO fc as compared with the previous days, many more individuals began to pupate on the 25th the total number reached 52, on the 26th it was 70. On the 27th the number was 85, and on the 28th 97 ; thus from day to day, there was again decrease in the number of pupae formed, so much so that on the 3rd March the total reached only 00; on this day the lid was removed permanently, and the next three days brought the number to 07, the remaining 3 did not pupate at all. Thus, evidently, suffocation instead of accelerating metamorphosis, which it should have done according to the asphyxia theory of Bataillon, retarded it to a great extent. 62

3 Studies on Insect Metamorphosis II. In another experiment, 50 full-grown larvae were put in a jar with the same concentration of CO S as in the above experiment, but in this case the mouth of the vessel was made TABLE II. Date of Total Number of Pupso formed to Date. Suffocated Series. Remarks. Started on 6/3/ 50 larv e subjected to suffocation Feb. 7, 0 a.m., 7, 6 p.m., 8, io a.m.,, 8, 6 p.m. 9, 0 a.m., 30, 0 a.m., 3, 4 p.m., 33, 0 a.m died O 49 did notpupate at all Lid of the CO. jar removed for hours. * almost air-tight. In an interval of three days (Table II.), while 49 out of 50 individuals kept in the normal atmosphere (control) pupated, none of the CO S lot metamorphosed. Then the lid of the CO, jar was taken off for twenty-four hours; TABLE III. Experiment started on 8/3/. D»te of Observation. Total No. of Pupso formed to Date. 300 cc Series. 200 cc Series. 00 cc Series. Feb. 9, 0 a.m. 20, 0 20, 4 p.m. 3, IO 2, 4,, 23, I» 23, 0 33, died after this the larvae began to change and 48 finished pupation within the next five days ; the remaining 2 died. III. In the third experiment, in three jars containing larvae each, 300 cc, 200 cc, 00 c.c. of CO S respectively were introduced. A fourth jar with the same number of 63

4 Hem Singh-Pruthi individuals but without any CO, in it served as control. The experiment was started on 8/2/25 (Table III.). By the 20th (4 p.m.) all the larvae in the control metamorphosed, in the CO, jars there were 3,, pupae in 00 c.c, 200 c.c, 300 c.c. jars respectively. On the 22nd ( p.m.) the totals in these jars reached, 29, 25 respectively. The last larvae in the 00 c.c. jar and the last 6 in the 200 c.c. jar pupated during the night between the 22nd and 23rd; the larvae in the 300 c.c. jar finished pupation on the 23rd at 4 p.m. ; one of this lot died. These results indicate that the degree of retardation of metamorphosis depends upon the concentration of CO S in the surrounding atmosphere. The results of the above experiments entirely contradict the asphyxia theory of Bataillon. It is not implied that his observations about the greater amount of CO, in the body of the pupating larvae was not correct, for recently Bishop (924) has also shown that there is greater tension of CO 3 in the spinning larvae of the Bee (Apis sp.). However, if one closely follows the descriptions of these authors it appears that the maximum amount of CO, noticed is on the day the individual pupates (Bataillon, p. and Curve IV.). But it is now generally admitted that metamorphosis in the real sense of the word, i.e., the beginning of changes in the internal organs, starts a few days before the individual actually pupates ; in a previous communication (925) it was shown that the insect larvae, after attaining maximum growth, begin to lose weight, indicating the beginning of histolysis inside the body, and this they do a few days before they change into pupae. If the accumulated CO S is the cause of metamorphosis, this accumulation must be shown to occur just when, or a little after, the larvae attain their maximum weight. An accumulation just before actual pupation, when histolysis is in full swing, cannot be considered the cause of this phenomenon, it seems to be rather its by-product. I wish to thank Mr F. Balfour-Browne, M.A., who watched the investigation with keen interest and made many valuable criticisms. My indebtedness is also due to Mr J. G. H. Frew, who supplied some very useful material. 64

5 Studies on Insect Metamorphosis References. Bataillon, E. (89), Ann. de I'Utdv. dt Lyon, 8. Bataillon, E. (893), Bull. Set. d. I. France et Belg., 88^ 8. Bataillon, E. (900), C. R. Soc. Biol., Paris, p. 4. Bert, P. (885), C. R. Soc. Biol., Paris, p Bishop, G. H. (923-4), Joum. Biol. Chem., 68, 543. Mercier, M. L. (907), Arch. Zool. Exper. et Gin. (4), B, 95. Perez, Ch. (903), Bull. Sci. d. I. France et Belg., 87,. Singh-Pruthi, H. (925), "Studies on Insect Metamorphosis. Starvation," Brit. Journ. Exper. Biol., III., I. Terre, L. (900), C. R. Soc. Biol., Paris, pp. 9, 58, 60. III. Effects of VOL. in. NO». 65