タケノホソクロバ幼虫の集合性の研究-2-

The female of Artona funeralis lays eggs in batch on the leaf of bamboo-grass. The larvae hatched from the egg batch keep the compact aggregation up to the third or fourth instar and then gradually disperse to one a leaf. The author pointed out in the previous paper (1962) that the larvae seemed to receive the effect of aggregation before the dispersal period and the density effect after that period. In 1962,to clear up those two effects on the mortality and the larval duration, one larva per vessel was isolated in each instar from members of aggregation with the replications of some twenty. In 1963 to analyse in more detail what effect do larvae receive on their development when reared in isolation before dispersal period, the larvae kept in isolation immediately aftert heir hatches were compared with ones having aggregated up to the end of the third instar and reared singly after the fourth instar with replications of about sixty. If the larvae were kept in isolation immediately after hatch their mortality was 20-30% in the first instar. Though they died little afterward for some instars, they died a little more again in the fourth or fifth instar. On the other hand, when the larvae were reared in the aggregation for all larval stages they did not die at all up to the third instar. Afterward the larvae, however, took extraordinarily high percentages of mortality. But larvae, reared in mass up to the third instar and singly after the fourth instar, died little for all larval stages. So he may be able to conclude that the larvae receive the ef fect of aggregation before dispersal period and the density effect after that period. Now the larvae isolated for all larval stages took the highest total mortality during larval stages and the ones isolated after the fifth did high in the second. When they were reared under the aggregated situation up to the end of the first, second or third instar and afterward under the solitary condition, they died little and there were little difference between those mortality. Those facts seem the dependency on aggregation is strongest in the first instar larvae and so suggest that if the damages, for example, parasites, predators, diseases or storms, destroy the aggregation of the first instar larvae, many solitary larvae will appeare and die secondarily in addition to the primary death. The larval durations tended to be shorter when the larvae were reared in the aggregated condition until the end of first to third instar and afterward under the solitary condition and also there were little differences between those durations as in the mortality. In the case of 1963,similarly, the larvae kept isolated for all larval stages developed more slowly in 2 or 3 days than larvae isolated after the fourth instar. Then in 1963 the fifth and sixth instar type larvae appeared in all two treatments. When the larvae were reared in isolation for their all larval stages, the proportion of the sixth instar type larvae was more. On the other hand when reared in isolation after the fourth instar, that was vice versa. And the larval duration of the sixth instar type larvae was longer in 3 or 4 days than fifth instar type larvae. Irrespective of instar types or sexes the larvae kept in isolation for their all larval stages developed a little more slowly. Accordingly the difference in the mean durations of both larvae kept in isolation for their all larval stages and after the fourth instar is determined by the frequency of those two instar types in each treatment in addition to the difference between the larval durations of the corresponding instar type larvae from two treatments. When it is compared between the larvae kept in isolation for all larval stages and after the fourth instar how long is the duration of their each instar, there is found no difference in the first instar and the former is a little longer afterward except the third instar, while in the third instar vice versa. Consequently the developmental du