Silkworm Diapause: Why Some Eggs Sleep and Others Don't

Two Kinds of Silkworm Egg

Some silkworm eggs develop straight through and hatch. Others enter a programmed dormancy called diapause and will not hatch for months, whatever you do to them. Which kind you have was decided before the egg was laid.

Voltinism: How Many Broods a Year

Silkworm strains are grouped by how many generations they run in a year:

• Univoltine — one brood a year. Suited to cold and temperate regions, and they lay diapausing eggs that overwinter.
• Bivoltine — two broods. Whether the eggs diapause depends on the conditions the parents experienced.
• Polyvoltine — many broods. Suited to the tropics, and they lay non-diapausing eggs that simply develop.

This is not a quirk of husbandry. It is the animal's ancestral answer to winter, kept intact through domestication.

The Mother Decides

Here is the part that makes diapause strange. Diapause is controlled by diapause hormone, and it acts through the mother — her physiology determines whether the eggs she lays will sleep. The egg does not decide; it inherits a decision already made.

The evidence is direct. Injecting diapause hormone into female pupae of a polyvoltine strain — one that normally lays eggs that hatch straight away — makes them lay diapausing eggs instead. Treating univoltine females with antibodies against the hormone does the reverse.

Why It Matters Commercially

Diapause is what makes silkworm eggs storable. A batch can be held cool and dormant, then started when wanted — which is the whole basis of scheduling a rearing operation rather than reacting to whatever hatches.

It is also why silkworm eggs and live silkworms have opposite requirements. Cool storage is correct for eggs and fatal for worms — a confusion that kills more cups than any pathogen.

Related: the silkworm's wild ancestor · what silk is made of