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1953
The Lepidopterists' News
5
A NOTE ON THE COLORS OF PUPAE OF PIERIS RAPAE DEVELOPED UNDER ARTIFICIAL CONDITIONS
by P. H. H. Gray
Ford (1945) states that the pupae of some butterflies "are either thought or known to be affected by their environment, but the subject is not well understood ... [and] ... is in need of further investigation." Poulton (1887) made a comprehensive series of experiments on P. rapae as well as on other butterflies; the backgrounds upon which the larvae pupated varied, as also did the amount of illumination. Scudder (1889) summarized Poulton's results, stating "white produced light chrysalids,.. .dark red produced dark chrysalids; deep orange very light green chrysalids". Harrison (1928) stated "It has ... long been known that the pigmentation of the pupae of the ... lepidopterous species ... P. rapae (Poulton 1887), is influenced by the colour of the light to which the larvae .. . are exposed just before pupation." Harrison experimented, however, with mixed broods of P. napi L. Recently Harrison (1951) bred a hybrid between P. napi and P. rapae and recorded that "Practically the whole of the thirty one chrysalids were, as might have been anticipated from their surroundings, light green in colour." (The cages were of white muslin net with Windolite tops.)
In 1951 the writer placed two series of eggs, each series from a separate female P. rapae, in closed one-pint ice cream cartons, in a basement receiving weakly diffused daylight. The temperature varied only between 68° and 72° F. The stem of the food-plant passed through a hole in each carton into a jar of water.
Experiment 1: This began with 100 eggs laid by one female on Arabis. After 17 days in the cartons the larvae were moved, in batches of 7, into 6 one-quart sealer jars for a humidity test; 13 larvae were kept in a carton. 41 pupae developed from these 55 larvae. The colors of the pupae did not appear to have been affected by the various moisture conditions. The colors, judged about 48 hours after pupation, were as shown in tabular form below.
Flesh, and flesh Green 2
with green tinge 8 Grass green 2
Gray 1 Sap green 1
Gray-green 7 Brown 2
Light green 2 Red-brown 1
Same, pink tinge 2 Black-brown 1
Emerald green 3
The colors of the other 9 were not recorded. 18 of the pupae were thus mainly green. It may be of interest to note that shortly before eclosion all of the 13 pupae in the carton changed to light flesh-color with light green abdomina. The empty shells of all the pupae were light flesh-color, ex cept those in the carton, which retained the green color on the abdomina.
6 GRAY: Pupal Colors of Pieris rapae Vol.7, no.l
Experiment 2: Larvae reared in cartons from eggs laid by another female on Barbarea vulgaris L. (Winter Cress) yielded 39 pupae, which were colored as follows:
Gray-pink 1 Sap green 2
Gray-green 7 Dull green 13
Green 8 Dark green 6
Grass green 1 Gray-brown 1
37 out of the 39 were thus some shade or hue of green.
Experiment 3: About 120 eggs were collected at random on leaves of Barbarea growing wild. The colors of 31 pupae that formed in jars were as follows:
Gray-green 8 Blackish green 5
Green 6 Brown 10
Brownish green 2
A large proportion of dark pupae thus developed in this random population. It was not possible to compare this set with wild pupae, for careful search among the leaves of the wild Barbarea revealed only 2 well-grown larvae, in spite of energetic laying by many butterflies.
Pupation dates were from July 31 to August 14; emergences from August 14 to 23, 1951.
These few experiments show that larvae of Pieris rapae, reared on their preferred foodplants in nearly complete darkness, or in diffuse daylight, yielded pupae which varied greatly in color. The colors of the pupae thus appeared to be independent of the background. The causes for such varied coloration may have to be sought in the hereditary constitution of the insect.
References
Fcrd, E. B., 1945. Butterflies. London.
Harrison, J. W. H., 1928. Induced changes in the pigmentation of the pupae of the butterfly Pieris napi L. and their inheritance. Proc. Roy. Soc. Ser. B., vol. 102: pp. 347-353.
Harrison, J. W. H., 1951. A hybrid between Pieris napi male and P. rapae female (Lep. Pieridae). The Entomologist, vol. 84: pp. 99-101.
Poulton, E. B., 1887. An inquiry into the cause and extent of a specific colour relation between certain exposed lepidopterous pupae and the surface which immediately surrounds them. Phil. Trans. Roy. Soc, vol. 178: pp. 311-441.
Scudder, S. H., 1889. The butterflies of the Eastern United States and Canada with especial reference to New England. Cambridge Mass.
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