Chromosome Count

by Bill Oehlke

Several months ago, one of the members asked me, "How do you find chromosome numbers for Saturnidae?"

I did not know the answer, but had read some information in Richard S. Peigler's and Stefan Naumann's excellent book, A Revision of the Silkmoth Genus Samia.

I wrote to Dr. Peigler and he wrote back.

"To find chromosome numbers, one must catch cells that have chromosomes undergoing mitosis. This is done in lepidoptera by catching spermatogenesis (production of sperm) in the testes of male pupae, a few weeks or days before the moths would emerge. Then it is a simple squash and stain technique on a microscope slide, hoping to find a cell with chromosomes in a phase that can be counted.

"The most complete list of chromosome numbers for saturniids is probably by Narang & Gupta, 1982, which may be easily accessible to you since it is in the Journal of the Lep Society. See JLS 36(2): 112-118 (1982). Those Indian authors tabulate their earlier papers and the results of other workers. They also give some figures of chromosomes and methodology."

I am a member of the Lep Society, but do not have the back issue cited. If anyone can send me a copy of the article it would be most appreciated. I have since received a copy of the article and present a summary at the close of this article.

Ric also gave me permission to provide the count numbers from the Samia revision, citing the original publications.

"The modal number for Saturniidae is n = 31, which is the number for many species in the genera Saturnia, Actias, Hyalophora, Antheraea, Cricula and even Automeris.... Callosamia promethea has a lower number, namely n = 19. This reduced number supports the hypothesis that Callosamia is closely related to Samia.

"The chromosome number for S. cynthia is n =13, based on stock from northeastern China (Liaoning, Shandong and Shanghai) and Korea examined by Yoshido (1953) and Wu (1962) and material studied by other workers.... The chromosome number for S. wangi from Taiwan is n =13. Material from Zhejiang showed fourteen pairs, and could have been either S. cynthia or S. wangi..... The number for S. canningi (Khasi Hills, Meghalaya, India), S. ricini (Korea and India) and S. pryeri (Japan) is n = 14."

I was reminded of Zak's question when Bruce Passarelli recently sent me an image of a pairing of a Samia cynthia male with a Callosamia promethea female.

Samia cynthia pairing with Callosamia promethea courtesy of Bruce Passarelli.

Bruce reported only a small number (13) of infertile eggs being deposited before the female died prematurely. Several years ago one of my female lunas paired with a male polyphemus. About half a dozen infertile eggs were deposited before this female also died prematurely.

I asked Dr. Peigler about the premature deaths and he indicated, "My guess regarding the females who died without laying many eggs is that they were ruptured by the males. This is mentioned by Collins & Weast in the 1961 book on page 116."

Unfortunately I do not have that resource either, and it is not in the U.P.E.I. library. More specific info would be appreciated.

There are at least two reports of success (live adult offspring) with Samia cynthia males and Callosamia promethea females. See end of article.

I am interested in more information about chromosome count and the mechanisms that seemingly allow hybridization between some species but not others. Help in this area would be much appreciated.

There are images of many beautiful hybrids in the hybrid section of the WLSS, and Dr. Peigler gave me permission to publish this image of a successful cross between a male Callosamia angulifera and a female Samia cynthia.

Image courtesy of Dr. Richard Peigler.

Tuskes, Tuttle and Collins also report a number of intergeneric crosses in their The Wild Silk Moths of North America, another excellent book. They report (males first) angulifera x cecropia; angulifera x cynthia; angulifera x gloveri; promethea x cecropia; securifera x cynthia; E. calleta x R. orizaba; cecropia x cynthia; cecropia x angulifera; cecropia x promethea; euryalus x atlas and cynthia x promethea. All of the pairings resulted in fertile eggs, but not all produced adults.

Adults have been obtained, however, from the cynthia x promethea pairings (Soule, 1902; Weast 1989)

Use your browser "Back" button to return to the previous page.

My father is offering Callosamia angulifera eggs this spring (2005-see April-May newsletters), and I suspect he will have cocoons again in the fall.

Summary of the R. C. Narang and M. L. Gupta paper:

Archaeoattacus edwardsii is examined and shows a record high chromosome count with diploid number of 128. Of the sixty-four pairs, one pair, believed to be the pair responsible for sex, is noticeably larger.

The other chromosomes in A. edwardsii are always smaller than chromosomes found in species with lower chromosome counts. This most likely indicates fission (splitting) among the A. edwardsii chromosomes. Possibilities of other arrangements "like inversions, translocations, etc., cannot, however, be disregarded."

The next highest count with 49 is found in Antheraea pernyi.

Those species with the median count of 31 include Actias selene, Actias luna, Antheraea frithi, Antheraea mylitta, Antheraea roylei, Antheraea yamamai, Caligula (Dictyoploca) simla, Graellsia isabellae, Actias (Sonthannaxia) maenas, Hyalophora cecropia, Hyalohora columbia, Hyalophora gloveri, Hyalophora euryalus, Automeris io and Dryocampa rubicunda.

Counts of 30 pairs are found in Antheraea polyphemus, Caligula (Dictyoploca) japonica, Saturnia pyri and Eriogyna pyretorum.

Those species with less than 30 pairs include Antheraeopsis assamensis (15), A. compta (15), Loepa katinka (28), Saturnia pavonia (29), Samia cynthia (13-14) and Callosamia promethea (19).