Cocoon spinning behavior in the silkworm, Bombyx mori : Comparison of three strains constructing different cocoons in shape

The spinning behavior of the silkworm, Bombyx mori, was recorded on videota pes from two angles and analysed by three dimentional computer graphics usi ng the Japanese (J. 124), Chinese (C.124) and their hybrid (J.124 x C.124) strains. These strains constructed typical peanut-shaped, spherical and ell ipsoidal cocoons, respectively. Linear representation of the spinning postu re revealed that larvae fixed the posterior half of the larval body (6th to 13th segment) and spun silk moving their anterior half (Ist to 5th segment ) for the most spinning period in all strains used. Little difference was o bserved in the average spinning speed among them. The Japanese strain spun primarily in a S-letter posture and changed its direction frequently. The l arva of Chinese strain often assumed a C-letter posture and showed directio n-changing behavior with comparatively lower frequency. The hybrid larva th rew the head back largely in an U-letter shape during most of the spinning period and showed cocoon expansion behaviors most frequently. The cocoon ex pansion behavior occurred mainly at both ends of the peanut-shaped cocoon ( J.124), at the center part of the spherical cocoon (C.124) and at both shou lders in the ellipsoidal cocoon of the hybrid strain. Thus, there exist str ain-specific features in the spinning behavior, and it is suggested that th e main behavioral factors affecting cocoon shape formation are the spinning posture and the cocoon expansion behavior during spinning.