Häggström Håkan, Larsson Stig
Department of Entomology, Swedish University of Agricultural Sciences, P.O. Box 7044 S-750 07, Uppsala, Sweden.
Oecologia. 1995 Nov;104(3):308-315. doi: 10.1007/BF00328366.
The slow growth/high mortality hypothesis predicts that herbivorous insects feeding on suboptimal host plants are subjected to higher predation mortality owing to the longer time spent in the vulnerable juvenile stages compared with conspecifics feeding on optimal plants. We tested this hypothesis for the willow-feeding leaf beetle Galerucella lineola raised on one suitable (Salix viminalis) and one unsuitable (S. dasyclados) willow species as well as on plants from an interspecific cross between the two species. Cohorts of larvae raised on caged plants (protected from enemies) and uncaged plants (exposed to enemies) were monitored daily throughout larval development in two consecutive years. Larvae raised on S. viminalis developed faster, grew larger and survived better than those raised on S. dasyclados. The suitability of the hybrid plants was intermediate to that of their parents. Our results strongly support the slow growth/high mortality hypothesis. In both years, total predation during the larval period was higher on S. dasyclados than on S. viminalis. Furthermore, the daily predation rate (i.e. the proportion of larvae preyed upon per day) was higher on S. dasyclados than on S. viminalis. When hybrid plants were included in the analysis total predation was positively correlated with both larval development time and daily predation rate. We suggest that high predation on beetles on low-quality plants is the combined result of their longer development time and elevated daily predation rate. The results are discussed in relation to the evolution of host plant selection and the paradox of sublethal plant defenses.
生长缓慢/高死亡率假说预测，以次优寄主植物为食的植食性昆虫，由于与取食最优植物的同种昆虫相比，其在易受伤害的幼虫阶段所花费的时间更长，因而遭受更高的捕食死亡率。我们以取食柳树的叶甲黄斑长跗萤叶甲为对象，对这一假说进行了验证，该叶甲饲养在一种适宜的柳树（垂柳）、一种不适宜的柳树（毛果柳）以及这两个物种间种间杂交产生的植株上。连续两年，在幼虫发育全过程中，每天监测饲养在笼养植物（免受天敌侵害）和非笼养植物（暴露于天敌）上的幼虫群体。取食垂柳的幼虫比取食毛果柳的幼虫发育更快、体型更大且存活率更高。杂交植物的适宜性介于其亲本之间。我们的结果有力地支持了生长缓慢/高死亡率假说。在这两年中，毛果柳上幼虫期的总捕食量均高于垂柳。此外，毛果柳上的每日捕食率（即每天被捕食幼虫的比例）高于垂柳。当将杂交植物纳入分析时，总捕食量与幼虫发育时间和每日捕食率均呈正相关。我们认为，低质量植物上甲虫的高捕食率是其发育时间延长和每日捕食率升高共同作用的结果。本文结合寄主植物选择的进化以及亚致死植物防御的悖论对结果进行了讨论。
