Races of Bombyx moriBased on voltinism & moultinism

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.,

Classification of Bombyx moriClassification based on:

•Distribution

•Moulting

•Voltinism

•Cocoon color

•Rearing period

•Larval markings

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

Voltinism in Bombyx mori

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

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

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.

How do they differ?

Diapausing eggs

• Also called as “Kuradone eggs”.

• Eggs remain in dormant stage

• It is produced by the 2nd generations of univoltine silkworms & 3rd 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

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 28 C⁰

• 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 28 C⁰

• 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

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)

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.

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.

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.