LIBRARY

LEPIDOPTERA 489
ning of written history been the most commercially important beneficial member
of the insect world. It is the basis of large industries not only in Asiatic
and European countries, where the caterpillars are reared and the raw silk
produced, but also in North America where much of the manufacturing of silk
products occurs. Many vain efforts have been made to establish sericulture
permanently in the United States! but the high cost of hand labor bas been the
limiting factor.
The Chinese silkworm is native to Asia and has been domesticated for so
many years that it can no longer exist without the care of the human race. By
careful selection many races have been developed to meet the various needs of
FIG. 160. Mature caterpillar of the Chineae or nlulberry silkworm, Bombyx mor; Linn.
(U.5.D.A.)
climate, rapidity of reproduction, color, quantity, and quality of the silk to be
produced.
The adult moths have a wing expanse of 40-45 mm., are robust and creamy
white, with several faint lines across the fore wings. The small smooth subspherical
eggs are first yellowish-white and become darker as the embryo
deVelops; each female lays about 300. The caterpillars are rough and wrinkled,
naked, whitish, attain a length of 45-55 mm., and have a short anal hom.
They feed on white and black mulberry leaves which are picked for them each
day but they will also eat the leaves of other mulberries, osage orange, and
even lettuce. Maturity is reached in 45 days and pupation occurs in a thick
oval white or yellow silken cocoon, The adults emerge in 12 to 16 days. There
are races of from one to six broods a year. For commercial purposes the PUPa;)
are killed in the cocoons by heat or hot water and the raw silk reeled for subsequent
use.
The larvre are subject to a severe hereditary disease known as pebrine which
is caused by a myxosporidian parasite, Nosema bombycis Nageli, and transmitted
from the moths through the eggs. It is possible to eliminate this disease by a
microscopic examination of the blood of the females and the use of eggs from
those free from contagion. The caterpillars are also subject to parasitism by
certain tachina flies which oviposit on the mulberry leaves and thus ,gai;n entrance
to the body by means of the alimentary tract. Silkworms are readily
reared in confinement by feeding the developing larvre tender and fresh daily
food. They remain in small uncovered containers and do not roam about if
unconfined as do the caterpillars of all our common moths.
lESSIG, E. 0" "The Silkworm," in liistory of Entomology, Macmillan, N. Y:, PI'. 231-236,
1931.