The fall webworm, Hyphantria cunea Drury, is inportant injurious insect. The webworm is native to North America. It has been introduced into some areas of Europe and Asia. Distributions in Japan: Tokyo, Kanagawa, Saitama, Chiba. Ibaraki, Gunma, Yamanashi, Aichi, Osaka, Okayama, Toyama, Niigata, Isikawa, Hyogo, Tochigi, Fukushima, Miyagi, Nagano, Akita, Iwate and Shizuoka.
This insect has been found feeding on more than 60 garden plants in Tokyo. This insect passes the winter in the form of brown pupae, enclosed in lightly woven, silken cocoons. These cocoons will be found under trash on the ground or sometimes under the bark of trees, the moths begin emerging during the spring and continue to come out over a long period. Both sexes are winged, satiny white, sometimes with brown or black spots. They lay their eggs on under side of the leaves, in masses, partly covei ed with white hairs, and the caterpillars hatching from these eggs construct webs over the leaves inside of which they feed. They continue feeding for about 1 month to 6 weeks, and upon becoming full-grown, crawl down the tree and construct the cocoons in which they pupate.
The adults emerge late in the summer and lay eggs for a second generation of the worms in early fall, which, upon becoming full-grown, spin the cocoons in which they pass the winter as pupae.
This paper presents results of a some biological study (head width in larvae, development and growth spead of larvae, food plants and habit, mechanism of population dynamics) made during 1959-65 on the Fall Webworm, Hyphantria cunea Drury in Tokyo.