Scientific American Supplement, No. 344, August 5, 1882

by Various

"I do not agree with the opinion expressed in one of your reports, that the short duration of the larva stage, caused by a high temperature, has the effect of diminishing the size of the cocoons, because the Atlas and Tusser cocoons produced at the sea-level here are quite as large as those found in the Central Provinces at elevations of three thousand feet or more. According to the treatise on the "Silk Manufacture," in "Lardner's Cyclopedia," the Chinese are of opinion that one drachm of mulberry silkworms' eggs will produce 25 ounces of silk if the caterpillars attain maturity within twenty-five days; 20 ounces if the commencement of the cocoons be delayed until the twenty-eighth day; and only 10 ounces if it be delayed until between the thirtieth and fortieth day. If this is correct, a short-lived larva stage must, instead of causing small cocoons, produce just the contrary effect."

In another letter, dated November 25, 1881, my correspondent says: "I am sorry that you have not had better success in the rearing of your larvæ, but you should not despair. It is possible that the choice of an improper food-plant may have as much to do with failures as the coldness and dampness of the English climate. I lost many thousands of Atlas caterpillars before I found out the proper tree to keep them on in a domesticated state; and when I did attain partial success, I could not keep them for more than one generation, till I found the Milnea roxburghiana to be their proper food plant. I do not know the proper food-plant of the Mylitta (Tusser), but I have succeeded very well with it, as it is a more hardy species than the Atlas. Though a Bombyx be polyphagous in a state of nature, yet I think most species have a tree proper to themselves, on which they are more at home than on any other plant. I should like, if you could find out from some your correspondents in India, on what species of tree Mylitta cocoons are found in the largest numbers, and what is about the greatest number found on a single tree. The Mylitta is common enough here, but there does not seem to be any kind of tree here on which the cocoons are to be found in greater numbers than twos and threes; and there must be some tree in India on which the cocoons are to be found in much greater plenty, because they could not otherwise be collected in sufficient quantity for manufacturing purposes. The Atlas is here found on twenty or more different kinds of trees, but a hundred or a hundred and fifty cocoons or larvæ may be found on a single tree of Milnea roxburghiana, while they are to be found only singly, or in twos and threes, on any other tree that I know of. The Atlas and Mylitta seem to be respectively the Indian relations of the Cynthia and Pernyi. It is, therefore, probable that the Ailantus would be the most suitable European tree for the Atlas, and the oak for the Mylitta."

Attacus mylitta (Antheræa paphia).--I did not receive a single cocoon of this species for the season 1881. My stock consisted of seven cocoons, from the lot received from Calcutta at the end of February, 1880. Five were female, and two male cocoons; one of the latter died, thus reducing the number to six. The moths emerged as follows: One female on the 21st of June, one female on the 26th, one female on the 28th, one female on the 1st of July, and one male on the 3d of August; the latter emerging thirty-four days too late to be of any use for rearing purposes. The last female moth emerged, I think, about the end of September. These cocoons had hibernated twice, as has been the case with other Indian species. I had Indian cocoons which hibernated even three times.

Attacus cynthia, from the province of Kumaon.--With the Atlas cocoons, a large quantity of Cynthia cocoons were collected in the province of Kumaon. Both species had, no doubt, fed on the same trees; as the Cynthia, like the Atlas cocoons, were all inclosed in leaves of the Berberis vulgaris, which shows that Cynthia is also a polyphagous species. It is already known that it feeds on several species of trees, besides the ailantus, such as the laburnum, lilac, cherry, and, I think, also on the castor-oil plant; the common barberry has, therefore, to be added to the above food plants.

These Kumaon Cynthia cocoons were somewhat smaller and much darker in color than those of the acclimatized Cynthia reared on the ailantus. The moths of this wild Indian Cynthia were also of a richer color than those of the cultivated species in Europe.

During the summer 1881, I saw cocoons of my own Cynthia race obtained from worms which had been reared on the laburnum tree. These cocoons were, as far as I can remember, of a yellowish or saffron color; which I had never seen before. This difference in the color of the cocoon was very likely produced by the change of food, although it has been stated, and I think it may be quite correct, that with many species of native lepidoptera the change of food-plants does not produce any difference of color in the insects obtained. With respect to the Cynthia worms reared on the laburnum instead of the ailantus, it may be that the moths, which will emerge from the yellow cocoons, will be similar to those obtained from cocoons spun by worms bred on the ailantus, and that the only difference will be in the color of the cocoons.

The Kumaon Cynthia cocoons, as I found it to be the case with Indian species introduced for the first time into Europe, did not produce moths at the same time, nor as regularly as the acclimatized species. The moths emerged as follows: One female on the 22d of July; one female on the 25th; one male on the 3d August; one female on the 19th; one male on the 28th of August; one male on the 2d September; one female on the 3d. A pairing was obtained with the latter two. Two males emerged on the 4th of September; one male on the 6th; one male and one female on the 22d; one female on the 23d; and one female on the 25th of September. Five cocoons, which did not produce any moths, contain pupæ, which are still in perfect condition; and the moths will no doubt emerge next summer (1882). As seen in my note, a pairing of this wild Indian Cynthia took place; this was from the evening of the 4th to the 5th of September. The eggs laid by the female moth were deposited in a most curious way, in smaller or larger quantities, but all forming perfect triangles. These eggs I gave to a florist who has been very successful in the rearing of silk-producing and other larvæ; telling him to rear the Cynthia on lilacs grown in pots and placed in a hot-house, which was done. The worms, which hatched in a few days, as they were placed in a hot-house, thrived wonderfully well, and I might say they thrived too well, as they grew so fast and became so voracious that the growth of the lilac trees could not keep pace with the growth of the worms. These, at the fourth stage, became so large that the foliage was entirely devoured, and, of course, the consequence was that all the worms were starved. I only heard of the result of that experiment long after the death of the larvæ; otherwise I should have suggested the use of another plant after the destruction of the foliage of the lilacs; the privet (Ligustrum vulgare) might have been tried, and success obtained with it.

Of such species as Attacus pyri, of Central Europe, and Attacus pernyi, the North Chinese oak silkworm, which I have mentioned in my previous reports, and bred every season for several years, I shall only say that I never could rear Pyri in the open air in London, up to the formation of the cocoon. As to Pernyi, I had, in 1881, an immense quantity of splendid moths, from which I obtained the largest quantity of ova I ever had of this species. I had many thousands of fertile ova of Pernyi, which I was unable to distribute. Many schoolboys reared Pernyi worms, but with what success I do not yet know. The number of fertile ova obtained from Pyri moths was also more considerable than in former years, which was due partly to the good quality of the pupæ, and partly to the very favorable weather in June, at the time the pairings of the moths took place.

Leaving these, I now come to the North American species.

Telea polyphemus.--As I have stated in former years, this is the best North American silkworm, producing a closed cocoon, somewhat smaller than that of Pernyi, but the silk seems as good as that of Pernyi.