Research and the pursuit of a bivoltine revolution

1: Beginnings

Yonemura’s research of 1919/20 into crossing the ‘indigenous’ multivoltine silkworms with Japanese bivoltines and using first-generation cross-bred eggs for commercial rearing was the key element in the third stage of the industry’s development. This was using a familiar and rather general effect, ‘hybrid vigour’ or heterosis. With the local Pure Mysore as the mother moth, crossed with a newly imported Japanese bivoltine race, C.nichi, for the male parent, a striking advance in productivity was achieved. For these silkworms the effect was so robust that it soon came almost to be taken for granted.

An elaborate, controlled system for the production of adequate quantities of the Pure Mysore stock was set up and maintained, but the supply of the bivoltine parent, usually identified simply as ‘Foreign Race’, received much less attention. Over the years it deteriorated to the extent that the hybrid worms sometimes became less productive for commercial rearing than Pure Mysore by itself would have been.

It was therefore as something thought of as altogether new and different to the old and failing ‘CB’, cross-bred, that a Bivoltine Programme – the term now used commonly for the first time - was started in the early 1970s. Previously it had been the view of the sericultural scientists that bivoltine hybrid rearing was not possible in the main South Indian sericultural areas. Dr S. Krishnaswami, in charge of the Mysore Central Sericulture Research Institute in the 1960s, had focused his institute’s research on silkworm crop losses and other causes for poor productivity. He identified the main reason as defective rearing and set about establishing methods that would be much more effective (Krishnaswami 1978). In breeding an NB (New Bivoltine) series for crossing with Mysore race mother moths, he almost incidentally demonstrated in the 1970s that superior bivoltine races could be produced and maintained in India as well as in Japan and other leading sericultural countries (Indian Silk 22, 1, 1983: 3-11).

This breeding success now provided the confidence needed for a more ambitious policy aim of producing bivoltine silk by crossing bivoltine races, rather than better multivoltine silk such as might result from improving the established practice of CB rearing. Bivoltine silk, from Japan and overwhelmingly from China, was the kind which dominated the international silk trade and offered the qualities by which fitness for that trade was measured. Hybrid vigour was still to be exploited but now by combining bivoltine races, usually mating a race of Japanese origin with another of Chinese. They were distinguished in shape: the Chinese were oval and the Japanese waisted, in a shape called ‘dumbbell’ and spelled variously in India.

The first trials began at CSRTI in Mysore in the early 1970s. Unlike the original CB, there was no priority for the mother moth and they could therefore be crossed in either direction: both male and female moths of each race could therefore be used. Commercial rearing began in 1973-74 in Karnataka, the next year in Tamil Nadu and in 1977-78 in Andhra Pradesh (Mahadevappa 1982).