Variation in leaf utilization sites among three Calystegia (Solanales: Convolvulaceae)-feeding leaf beetle species...

In general, two or more species sharing the same niches are considered unable to coexist stably; instead, they either partition their niches spatiotemporally or compete, with one or more species eventually being excluded. Spatial niche partitioning is a common mechanism facilitating species coexistence. Three leaf beetle species, Aspidimorpha difformis (Motschulsky), Aspidimorpha transparipennis (Motschulsky), and Laccoptera nepalensis Boheman (Coleoptera: Chrysomelidae) appear to share spatiotemporal niches, as they all inhabit patches of Calystegia spp. R. Br. (Solanares: Convolvulceae) from spring to fall. Under rearing conditions, L. nepalensis excludes coexisting A. difformis but not A. transparipennis, by reducing the availability of oviposition sites on leaves. Given that herbivorous insects can exhibit resource preferences at fine spatial scales within leaves, this suggests that differences in leaf utilization sites between the two Aspidimorpha species determines their competitiveness against L. nepalensis. Here, we compared the feeding and oviposition sites within leaves among the three beetle species using spatial analysis and clustering. The feeding sites of L. nepalensis and the oviposition sites of A. difformis overlapped considerably, whereas the oviposition sites of A. transparipennis were largely unexploited by the others. All three species preferred lamina-abundant regions within leaves for oviposition, but this preference was weaker in L. nepalensis. Although it should be noted that this insight is based on limited data, these findings suggest that A. difformis is disadvantaged due to a higher risk of resource shortages. We argue that spatial analysis of consumption sites within leaves can more actively discuss spatial niche partitioning among herbivorous insects.