The following points highlight the top two methods adopted for rearing of bivoltine moths. The methods are: 1. Breaking Diapause 2. Adopting JICA Programme.
Rearing of Bivoltine Moths: Method # 1.
Breaking Diapause:
Bivoltine moths basically belong to temperate country like Japan. Their hibernating eggs pass through a period of diapause especially during winter for 6-8 months when availability of mulberry leave is a problem.
The eggs, therefore, do not hatch and the young’s live on reserve energy drawn from glycogen in the yolk. Rearing bivoltine moths in tropical and sub-tropical countries (e.g., India), where mulberry is available round the year, requires a breaking of their natural diapause and inducing hatching through acid treatment of the eggs. Thus, bivoltine moths can be reared over a long period and even up to 5 hatchings in a year.
Rearing of Bivoltine Moths: Method # 2.
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Adopting JICA Programme:
To tropicalising bivoltine sericulture in India. Dr. Kawakami of JICA has introduced several modifications to traditional silkworm rearing. Multivoltine moths are adapted here for generations which are more and more hardy, whereas bivoltines are more susceptible to nuclear polyhedral virus (NPV) and hosts of other bacterial, protozoal and fungal pathogens.
Rearing bivoltine moths in India thus needs some modifications like:
(i) Shoot Rearing:
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Unlike traditional practice of feeding with mulberry leaves, the late stage larvae in JICA approach are subjected to ‘shoot rearing’, i.e., leaves are not separated from the mulberry shoot. This not only save labour and time, but also inhibits secondary contamination from pathogens by keeping the leaves fresh for a longer time.
(ii) JICA-Modified Approach:
Here, the farmers directly rear the 3rd stage-larvae instead of eggs. The first two out of five instars are highly susceptible to diseases and demand high level of hygiene which the farmers cannot easily ensure.
Therefore, instead of supplying eggs to farmer, 3rd stage larvae may be supplied to them. The young larvae are maintained in special Chawki centres with controlled temperature and humidity and then handed over to farmers.