Races of bombyx mori

the major races of silkworms based in voltinism and moultinism

1. Races of
Bombyx mori
Based on voltinism &
moultinism

2. RACES:
A population within a species that is distinct in some way,
especially a subspecies.
Indigenous- originating in and characteristic of a particular
region or country; native.
Eg., Pure Mysore, Nistari.
Exotic- plant or animal species introduced into an area
where they do not occur naturally, non-native species.
Eg., E16, Daizo etc.,

3. Classification of Bombyx mori
Classification based on:
•Distribution
•Moulting
•Voltinism
•Cocoon color
•Rearing period
•Larval markings

4. Voltinism
It is the ability of many insect groups to produce from one
to several generations a year.
•Species producing one generation a year -univoltine
•Species producing two generations -bivoltine
•Species producing several generations -multivoltine

5. Voltinism in Bombyx mori

6. Univoltine races:
•produce ONE generation per year.
•larval weight is comparatively higher and
cocoons are heavy.
•Denier of the silk filament is above 2.3.
•not suitable for summer & winter rearings,
since the larvae are weak against
unfavourable conditions.
•They lay only diapausing eggs.
•All European races are univoltines eg.,E16

7. Bivoltine races:
•produce TWO generations per year.
•length of the larval stage is short.
•The leaf consumption to cocoon production
is less, and the quality of the cocoons inferior
to that of Univoltine races.
•cocoon weight, shell weight, silk % &
filament length lesser than uni/mono
voltines.
•Most of the temperate races are bivoltines
•Lay both non hibernating and non
hibernating eggs
•eg.,NB4D2, NB18, KA, NB7 etc

8. Multivoltine races:
•produce more than 5-6 generations per year.
•length of the larval duration is short.
•In most of the polyvoltine races the leaf
cocoon ratio is high
•the length of the filament is short
•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.
•eg.,pure mysore, c.nichi, hosa mysore.

10. How do they differ?
Diapausing eggs
•Also called as “Kuradone eggs”.
•Eggs remain in dormant stage
•It is produced by the 2
nd
generations of
univoltine silkworms & 3
rd
generations
of bivoltine silkworms.
•Eggs are dark brown before entering
to diapause stage
•Diapause can be broken by some
treatments such as acid treatment.
Non diapausing eggs
•Also called as “Nomadane eggs”.
•Eggs are not dormant.
•It is produced by the multivoltine
silkworms
•No color change, but turns bluish
black before hatching.
•No treatment required

11. How do they differ?
Bivoltine race
•Eggs may be diapausing or non
diapausing
•Loose egg production is mostly done
•Relatively poor disease resistant
•Cannot tolerate beyond 28⁰C
•Completes lifecycle in _______ days
•Eggs can be preserved upto 6-10
months
•1500-1700 eggs/ gram
•Shell ratio of 20-25
•Filament length 1000-2600m/ cocoon
Multivoltine race
•Non diapausing eggs are produced
•Flat card\ sheet method is done
•Relatively disease resistant
•Can tolerate beyond 28⁰C
•Completes the lifecycle in 26-27 days.
•Eggs cant be stored for more than 20
days
•1800-2100 eggs/gram
•Shell ratio of 12-14
•Filament length 400-500m/ cocoon

12. Moultinism
It is the classification based on number of moultings
throughout the lifecycle.
Silkworms can be classified into:
•tri moulters
•tetra moulters
•penta moulters
•hexa moulters (very rare)

13. Trimoulters:
•They moult three times during larval period.
•The larval growth is limited
•Short larval duration ranging from 15-18 days.
•Pupae & moths are small.
•Cocoon weight is less, cocoon filament is fine & denier of the silk filament ranges
from 1.6 to 1.7.

14. Tetramoulters:
•They moult four times during their larval stage.
•Medium the larval stage ranging from 23-28 days.
•Medium larval growth and cocoon weight.
•Denier is 2-2.5.
•Tetra moulters are cosmopolitan in their distribution.
•Most of the commercial silkworms belong to this group.

15. Pentamoulters:
•They moult five times during their larval stage.
•The length of the larval stage is long
•Larval weight is high and cocoons are heavy, filament length is more.
•Denier of the silk filament is very high.