2009 Volume 60 Issue 2 Pages 128-134
Larval development and diapause of the alien nymphalid butterfly Hestina assimilis assimilis, which was accidentally introduced into Kanagawa Prefecture, central Japan were re-investigated under various temperature conditions at a short and long photoperiod. In particular, influence of low temperature (15℃) linked with long photoperiod (16L-8D) on larval diapause induction was studied. First, when larvae were kept at 15℃, most of the larvae entered a diapause state mainly at the 4th instar irrespective of a long photoperiod while all larvae normally entered a diapause state at a short photoperiod. At 20℃ or 25℃, photoperiodic response was clear and similar to the results in the previous experiments (Kato and Miyauchi, 2008). Second, low temperature treatment under a long photoperiod was carried out at a particular developmental stage. The results showed that low temperature treatment at single larval instar stage had little effect on diapause induction, but the treatment of successive instars (such from 2nd, 3rd or 4th instar) was effective, and the longer the treated duration, the higher the diapause ratio. These results suggest that low temperature alone is responsible for larval diapause induction of this subspecies. Further, some larvae in which diapause had been induced by low temperature associated with a long photoperiod had a long or intermediate type horn, and their body color frequently was green, suggesting that diapause programs of the larvae are easily modified by these temperature conditions. In addition, such irregular diapause-related phenomena are discussed from the point of view of ecological significance, based on information of field observations.
