Phototactic Behavior in the Silkworm, Bombyx mori. I
Adaptive Significance of Phototaxis in Newly Hatched Larvae
1981 Volume 19 Issue 2 Pages 41-49
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1981 Volume 19 Issue 2 Pages 41-49
To determine the adaptive significance of phototactic behavior in newly hatched silkworm larvae, some experiments were designed and performed.
1) Before being fed mulberry leaves, the larvae showed active klinophototaxis (Fig. 2) .
2) The phototactic response-intensity curves showed a threshold for the response between 10-3 and 10-2lux after dark-adaptation, and between 10-2and 10-1lux after light-adaptation (Fig. 3) .
3) The shape of the light source toward the newly hatched larvae oriented themselves affected the phototactic response (Fig.4) .
4) In the visual region, the newly hatched larvae showed a maximum phototactic response to green irradiation (557 nm), but scarcely responded to blue and red irradiations (Fig. 5) . Larvae also responded to an ultraviolet irradiation of 357 nm. The light transmitted through the mulberry leaf had a remark-able attraction for the newly hatched larvae (Fig.6) .
5) The tactic activity by which the newly hatched larvae oriented and moved toward the mulberry leaves was lower in complete darkness than under light. Blind larvae, which had lost their vision and phototaxis due to a defect in vitamin A showed a reduced tactic response to mulberry leaf, irrespective of darkness or of light conditions (Figs.7 and 8) .
6) These results show that the larval phototaxis mediated by vision is important for finding and ar-riving at the green leaves of the host plant (mulberry) as is chemotaxis (Fig.9) .
