Effects of individual variation of host plants on the pattern of host selection in a phytophagous ladybird beetle species.

在北海道中部的札幌，以泡状瓢虫Epilachna pustulosa及其寄主植物蓟（Cirsium kamtschaticum）和蓝升麻（Caulophyllum robustum）为材料，研究了植物个体差异和种间差异对多食性植食性昆虫寄主选择的影响。通过成虫食物选择试验和饲养幼虫的叶片，从一些个别的植物，它表明，蓟和蓝升麻构成一个连续的系列的食物资源E.pustulosa和甲虫选择，无论植物种类，植物上，其幼虫将表现良好。然而，通过实验室实验获得的结果是矛盾的模式，在现场实现的主机selectivity;在实验室中首选的植物并不总是在现场使用，反之亦然。因此，脓疱棘球绦虫对寄主的选择不仅受实验室已阐明的因素的支配，而且还受某些影响尚不清楚的其他因素的支配。寄主植物的空间分布格局和生物量、甲虫的生境偏好以及甲虫与植物的物候对应关系可能是这些未知因子的候选者。我们还利用采集自北海道南部的蓟和蓝升麻进行了初步的寄主选择试验，在那里，E.niponica和E.yasutomii与E.pustulosa密切相关，但分别专化蓟和蓝升麻。在这种情况下，E.pustulosa也选择了特定的股票，而不考虑植物物种。

Effects of individual variation and interspecific difference of plants on host selection by polyphagous phytophagous insects were studied using a ladybird beetle Epilachna pustulosa and its host plants thistle (Cirsium kamtschaticum) and blue cohosh (Caulophyllum robustum) in Sapporo, central Hokkaido. Through adult food choice tests and rearing of larvae using leaves from a number of individual plants, it was shown that thistle and blue cohosh constitute a continuous series of food resource for E.pustulosa and that the beetles select, irrespective of the plant species, the plants on which their larvae will perform well. However, the results obtained by laboratory experiments were contradictory to the patterns of host selction realized in the field ; the plants preferred in the laboratory were not always utilized in the field, and vice versa. Host selection by E.pustulosa is thus governed not only by the factors clarified in the laboratory but also by certain other factors whose effects are not yet clarified. Spatial distribution patterns and biomasses of host plants, habitat preference of beetles, and phenological correspondence between beetles and plants are possible candidates of such unknown factors. We also conducted preliminary host choice tests by E.pustulosa using thistles and blue cohosh collected in southern Hokkaido where E.niponica and E.yasutomii, closely related species to E.pustulosa but specialized to thistle and blue cohosh, respectively. In this case, too, E.pustulosa chose particular stocks irrespective of the plant species.