Silkworm

lntroduction
The diapause, in insects, is a method of overcoming unf avourable period caused either by physiologically
unfavourable conditions or non-availability of food. For the silkworms ol the temperate region, both
these conditions will prevail during winter and thus they have developed the diapausing (hibernating)
character lo overcome this period.
The phenomenon of diapause is environmentally, physiologically and genetically controlled. Acid
treatment is just a method to change the physiology by blocking certain activities and inducing several new
biochemical reaclions lor the continuous development of the eggs.
Diapause eggs are more customarily relerred to as hibernating or bivoltine eggs, while lhe nondiapause
ones as non-hibernating or multivoltine eggs.
Left to themselves, the diapausing eggs do not hatch on incubation. However, it is possible to make
them hatch artif icially by providing various physicalor chemical stimuli. The various physical and chemical
agents/methods by which it is possible to block or lerminate the diapause are given in Table-1 . Though
several artificialmethods have been devised, the immersion of diapausing eggs in Hydrochloric acid (HCl)
has been the best choice and most widely adopted technique for immediate hatching, lrom the technical
as well as practical points of view, both at the laboratory as well as commercial leveis of bivoltine seed
production.
To bring a shift f rom diapause to non-diapause type, changes in the incubation schedule like shorter
exposure to light and low temperature during incubation, changes in the rearing conditions like continuous
high temperature rearing, low temperature during early stages and high temperature during the late
stages, cocoon preservation at high temperature, coupled with selection, are essential.
The scope of this booklet however has been restricted to methods ol acid treatment of diapausing
eggs for artificial hatching and related changes. This has been dealt with in two parts, Part - | dealing exclusively
with the methods of Hydrochloric acid treatment and Parl-ll with the physiological changes
associated with it.
Table
Agents/Methods of Artificial Hatching
Physical Stimulants
1. Artilicial overwintering by subjecting to low temperature*
2. lmmersion into hot water
3. Electrical stimulation using high voltage
4. Friction by feather/hard brush
5. Enforcement of high atmospheric pressure
6. Use of ultra high frequency vibrations
7. Use of radiated sunrays or exposure to sun-shine
8. Use of ultra purple rays/ultra short waves
9. Expozure to Oxygen
Chemical Stimulants
Hydrochloric acid .
Nitric acid
Sulphuric acid
Aqua - regia
Acetic acid
Sodium chloride
Hydrogen peroxide
Enzyme treatment
Ozone treatment
. Most commonly used methods/agents