|[Note Guidelines] Photographer's Note|
|Polygonia c-aureum The Asian Comma|
The Asian Comma can be distinguished from its European cousin (P. c-album) by the pale blue spots in the post-discal area of the hindwings. Two quite distinct seasonal forms, the summer form and autumn form, exist in adults of this butterfly. The picture shown here is of the autumn form, having been taken in November. The summer form appears to be paler in general colour.
While browsing for information on this species, I came across some interesting experimental conclusions about the way in which the two forms are determined and about the different life expectancies of the adults of the two forms. Although the note becomes a bit lengthy, I have reproduced the main conclusions below.
"Experiments were carried out to discover the factor(s) of their determination. When reared under a day length of 14 hours or above, larvae pupated to produce adults of the summer form regardless of temperature condition. Larvae submitted to a day length of 12 hours or below, produced adults of the autumn form regularly here again regardless of temperature. Among the group kept under 13 hours' day length throughout the larval and pupal period, emergence of adults of both summer and autumn forms occured, without formation of any intermediate forms. These results seem to indicate that the adult seasonal form of this butterfly is determined by the photoperiodic condition of the younger period. Long-day condition induces appearance of the summer form, while short-day determines that of the autumn form, the critical day length being around 13 hours. Other experiments showed the likelihood that this determination is made during the larval period, especially during the last two instars. Further studies on the same lines are needed for the understanding of the photoperiodic reaction in this species.
Observation of the ovarian development in adults of both forms demonstrated that the individuals of the autumn form were in a state of imaginal diapause, where the ovarian development occurred only about one month after emergence. This was considerably later than in individuals of the summer form in which ovaries were mature within a week. Mating and oviposition took place successfully, however, in such one-month-old adults of the autumn form. The eggs hatched normally, yielding normal adults. The life of the autumn-form adults exceeded 6 months, in contrast to that of the summer form which never lasted more than one month. This fact again confirms the diapausing nature of the autumn form.
It follows therefore that Polygonia c-aureum is one of the butterflies with a 'long-day type' development, to which Inachis (=Nymphalis) io is known to belong (Danilevsky, 1961). Its mode of seasonal form determination is quite different from the case of Araschnia levana (Muller, 1955) where the form of adult is determined immediately by the diapausing or non-diapausing nature of the pupa which, in turn, is determined by the photoperiodic condition during the larval life. In Polygonia, no pupa is diapausing, and the diapause seems to be inseparably bound to the seasonal form of the adult."
Reference: Laboratory of Biology and Agricultural Entomology, Tokyo University of Agriculture and Technology
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