Larval survival of the phytophagous ladybird,Epilachna yasutomii (Coleoptera,Coccinellidae), on the blue cohosh,Caulophyllum robustum (Ranunculales,Berberidaceae), grown under different environmental conditions

Larval survival of four local populations ofEpilachna yasutomii in the southern part of Nagano Prefecture was evaluated on leaves of blue cohosh,Caulophyllum robustum, growing at two different sites, Takatoh and Nakatachi. Based on larval survival on leaves of TakatohC. robustum, TakatohE. Yasutomii was clearly distinguishable from the three populations in the Minami-Shinano area (Akasawa, Nakatachi and Tenryu). TakatohE. yasutomii developed successfully to emergence onC. robustum from both sites, while Minami-Shinano populations showed a very low survival rate when given TakatohC. robustum. Under controlled plant growth conditions, larval survival of AkasawaE. yasutomii was significantly reduced when givenC. robustum leaves, from either site, exposed to direct solar radiation, which suggested that larval survival was influenced by environmental conditions at the growing sites rather than genetic differences between the plant populations. In contrast, TakatohE. yasutomii developed well onC. robustum leaves from either site exposed to direct solar radiation. TakatohE. yasutomii appears to have some defensive mechanism that allows it to overcome a substance deterring larval development, which increases in leaves exposed to direct solar radiation.