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

在北海道中部札幌市，以瓢虫Epiachna pustulosa及其寄主植物蓟和蓝升麻为材料，研究了植物个体变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用几种植物的叶片饲养幼虫，结果表明，蓟和蓝升麻构成了一系列连续的化脓性粉虱的食物来源，并且甲虫选择幼虫能在其上表现良好的植物，而不考虑植物种类。然而，实验室试验的结果与田间实现的寄主选择模式相矛盾，实验室喜欢的植物并不总是在田间利用，反之亦然。因此，泡囊棘球绦虫对寄主的选择不仅受实验室中已阐明的因素控制，而且还受某些其他因素的影响，这些因素的影响尚不清楚。寄主植物的空间分布格局和生物量、甲虫的栖息地偏好以及甲虫和植物之间的物候对应关系可能是这些未知因素的候选因素。我们还利用在北海道南部采集的蓟和蓝升麻进行了初步的寄主选择试验，其中尼波尼察和yasutomii是分别专属于蓟和蓝升麻的亲缘关系较近的物种。在这种情况下，脓毛E.pustulosa也选择了特定的种群，而不考虑植物种类。

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.