New Strain of Samia ricini Eggs

We have obtained a new strain of eri silkmoth (Samia ricini) eggs.

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This was rather unexpected, but this week a very generous breeder of Samia ricini offered us some eggs since they had more than they could rear. Although we already have our own stock of Samia ricini, we took the kind offer anyway in order to add genetic diversity to our stock and to see any differences between the strains, since Samia species can sometimes be quite variable depending on their origin. 

Well, when the eggs arrived, we moved them to a small petri dish and just from the naked eye they look more or less the same as the ones from our own stock, which is to be expected. However, enclosed with the package of eggs were also two very nice cocoon shells, and straight away we noticed quite a few differences between the silk texture and shape of the cocoons compared to ones from our old stock. First of all, the ones from the new stock are very large and thick, being noticeably more voluminous than even our largest cocoon. It's not so much that they are that much wider or longer, but they are more of a perfect egg-like shape rather than a flat tear-drop shape like ours, which gives them much more volume. The shells of the new cocoons are also much thicker and the silk used itself also seems much stronger and denser. In addition, the color of the new cocoons' silk is also a very pure shade of white, almost matching the paper color, while our old ones are a somewhat tannish off-white. It also amazes us how perfectly smooth and well-shaped the new cocoons are compared to our old ones which are mostly quite wrinkly and irregularly shaped, more closely resembling the cocoons of Samia cynthia.

We're not quite sure if all these differences between the cocoon shells of the two strains is attributed to genetics, or if the host plant they were reared on had a significant role. The new ones were reared on castor bean (Ricinus communis), Samia ricini's most preferred host plant, which we have never used. This might explain the new strain cocoon's superior size and silk quality. In fact, many studies out there have shown that larvae grow fastest, are less prone to disease, and produce the best quality cocoons when fed on castor bean. This could readily account for the differences we observed, but alternatively, the new strain could have also undergone much more intense selection for higher quality silk through the silk industry than our strain, which would also improve their cocoon size and silk quality. Whatever the case is, we'll rear both the old and new strains out this spring which should shed light on this topic. We'll also get to see the differences between the larvae and adults of the two strains, which should be at least as variable as the cocoons. 

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Authors
Alan Liang

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