Abstract
The purpose of the present study is to throw light on the genetical control of phototactic behaviors in the silkworm, Bombix mori.
Different four silkworm strains showing clear cut differential walking responses to light at the stage of mounting in cocooning frames under a light condition in an ordinary rearing room have been analyzed their phototactic behaviors throughout the whole larval stages. Among the tested four strains, two mutant strains, nb and pe; ok, were of photopositive and the other two strains, st and Ze; pe; re, were of photonegative. The larval phototactic behavior was measured by a mean walking distance (in centimeter) from the start line to either light or dark parts in a silkworm phototactic measurement apparatus (Fig. 1) .
The result of experiments indicated that a remarkable phototactic response is observed at the stage of mature larvae, but no significant response is observed in other larval stages. At the stage of matured larvae phototactic behaviors of the tested four strains were parallel with those of each strain at the mounting stage. Not yet completed analyses, however, the result of cross experiments between photopositive and negative strains showed that larval phototactic behaviors of F1 (or F2) hybrids seem to cover both parental behaviors. Though the tendency of the larval phototactic behavior of F1 (or F2) hybrids was somewhat photonegative rather than neutral, regardless of parent.
These findings may suggest that the nature of larval photonegative characters in the silkworm is more or less dominance than that of photopositive ones and factor (s) manifesting the larval phototactic character is controlled by polygenes.
