Voltinism is a term used in biology to indicate the number of broods or generations of an organism in a year. or Number of generations per year under natural environmental conditions. Based on voltinism, Bombyx mori is divided in to 3 types, namely
i) Univoltines, ii) Bivoltines and iii. Multivoltines.
i) UNIVOLTINE RACES:
- They produce ONE generation per year.
- The larval weight is comparatively higher and cocoons are heavy.
- Denier of the silk filament is above 2.3.
- They are not suitable for summer & winter rearings, since the larvae are weak against unfavourable conditions especially to higher temperature.
- They lay only diapausing eggs.
Example: All European races are univoltines e.g., E16.
ii) BIVOLTINE RACES:
- They produce two generations per year.
- The length of the larval stage is short.
- The leaf consumption to cocoon production (cocoon ration) is less, and the quality of the cocoons inferior to that of Univoltine races. Further, cocoon weight, shell weight, silk % & filament length lesser than uni/mono voltines.
- Most of the temperate races are bivoltines and lays both non hibernating and non hibernating eggs
Example: NB4D2, NB18, KA, NB7 etc.
iii) multivoltine races:
- They produce more than 5-6 generations per year.
- The length of the larval duration is short. In most of the polyvoltine races the leaf cocoon ratio is high, cocoons are compact grained and cocoon layer is soft.
- The length of the filament is short (approximately 400 mts). However, the cocoon filament is fine and clean with little lousiness; but with more lustrous.
- The larvae are robust and can tolerate fluctuating environmental conditions and hence best suited for tropical climates.
- They lay only non-diapausing eggs.
Example : Pure Mysore, C. nichi, Hosa Mysore.