Life Cycle Of B Mori

Silkworms undergo complete metamorphosis (Fig. 2). Larvae feed on the leaves of the mulberry (family Moraceae, genus Morus); they will consume other genera in this family, but growth rate is reduced. At 23 to 25°C the five instars require 25 to 30 days to hatch. Toward the end of fifth instar, B. mori spin a cocoon over a 3-day period and pupate within that cocoon; the pupal stage lasts for about 10 days. After molting to the adult has occurred inside the cocoon, the moth emerges. The moth softens the cocoon by orally excreting a

FIGURE 2 Life cycle of B. mori reared at 23 to 25°C. [From Mori, T. (1970). Life cycle of Bombyx mori. In "The Silkworm—New Experimental Tool in Biology" (T. Mori, ed.), p. 17. Sanseido Press, Tokyo.]

special enzyme, cocoonase, and then emerges from the end of the cocoon. The female moth mates the same day as emergence and begins egg deposition. One generation of B. mori spans 40 to 45 days.

Voltinism (i.e., the number of generations occurring in a single year) has a genetic basis, but it is also strongly affected by environmental factors. Some races are univoltine (only one generation a year); others are bivoltine (two generations a year) or polyvoltine (three or more generations a year, as seen in tropical silkworms that do not undergo diapause). Voltinism is closely tied to the geographic distribution of silkworms, which are divided into Japanese, Chinese, European, and tropical races. Typically, the silkworms distributed in the cold regions are univoltine, those distributed and adapted to warm regions are bivoltine, and those in tropical regions are polyvoltine.

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Bee Keeping

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