Abstract
In the armyworm, Leucania separata, the black larvae appeared in crowded population are different in many respects from the pale larvae in sparse population. This paper deals with the different reactions of these two types of the larvae to some mechanical stimuli.
When the larvae were dropped onto an illuminated field, they remained immobile for some time and then began to escape away. Most of the black larvae resumed their activity within one minute since being dropped, while a considerable percentage of the pale larvae showed a prolonged immobilization over five minutes. The difference was similarly observed in both experiments in which the larvae were dropped individually in a group.
After the recovery from the inactive state, the pale larvae tended to move into dark place more than the black ones. The photonegative tendency of the former was, however, reduced considerably when a group of the larvae was dropped simultaneously.
The difference was also observed in their grasping behaviour; the pale larvae clinged more firmly to the plant than the black ones when exposed to a strong wind.
These results are to be regarded as additional evidences of the fact that the pale larvae are passive and station-keeping, while the black ones are active and mobile in habits.
