Data from: Trichobaris weevils distinguish amongst toxic host plants by sensing volatiles that do not affect larval performance

Herbivorous insects use plant metabolites to inform their host plant selection for oviposition. These host-selection behaviours are often consistent with the preference–performance hypothesis; females oviposit on hosts that maximize the performance of their offspring. However, the metabolites used for these oviposition choices and those responsible for differences in offspring performance remain unknown for ecologically relevant interactions. Here, we examined the host-selection behaviours of two sympatric weevils, the Datura (Trichobaris compacta) and tobacco (T. mucorea) weevils in field and glasshouse experiments with transgenic host plants specifically altered in different components of their secondary metabolism. Adult females of both species strongly preferred to feed on D. wrightii rather than on N. attenuata leaves, but T. mucorea preferred to oviposit on N. attenuata, while T. compacta oviposited only on D. wrightii. These oviposition behaviours increased offspring performance: T. compacta larvae only survived in D. wrightii stems and T. mucorea larvae survived better in N. attenuata than in D. wrightii stems. Choice assays with nicotine-free, JA-impaired, and sesquiterpene-over-produced isogenic N. attenuata plants revealed that although half of the T. compacta larvae survived in nicotine-free N. attenuata lines, nicotine did not influence the oviposition behaviours of both the nicotine-adapted and nicotine-sensitive species. JA-induced sesquiterpene volatiles are key compounds influencing T. mucorea females’ oviposition choices, but these sesquiterpenes had no effect on larval performance. We conclude that adult females are able to choose the best host plant for their offspring and use chemicals different from those that influence larval performance to inform their oviposition decisions.植食性昆虫可借助植物代谢物筛选寄主植物，以此指导产卵决策。这类寄主选择行为通常符合偏好-性能假说（preference–performance hypothesis）：雌虫会将卵产于能最大化子代生存表现的寄主之上。然而，对于具有生态学相关性的物种互作关系而言，用于指导产卵选择的代谢物，以及导致子代生存表现差异的代谢物仍未明确。本研究针对两种同域象鼻虫——曼陀罗象甲（Trichobaris compacta，简称T. compacta）与烟草象甲（T. mucorea）——开展了田间与温室实验，实验所用寄主植物为次生代谢组分经特异性改造的转基因植株。两种象甲的雌成虫均更偏好取食D. wrightii叶片而非N. attenuata叶片，但T. mucorea雌虫更倾向于在N. attenuata上产卵，而T. compacta仅会在D. wrightii上产卵。此类产卵行为可提升子代适合度：T. compacta幼虫仅能在D. wrightii茎秆中存活，而T. mucorea幼虫在N. attenuata茎秆中的存活率显著高于D. wrightii茎秆。针对无尼古丁、茉莉酸（JA）功能受损以及过表达倍半萜的同基因背景N. attenuata植株开展选择实验结果显示：尽管有半数T. compacta幼虫可在无尼古丁的N. attenuata株系中存活，但尼古丁并未对适应尼古丁与对尼古丁敏感的两类象甲的产卵行为产生影响。茉莉酸诱导的倍半萜挥发物是调控T. mucorea雌虫产卵选择的关键化合物，但此类倍半萜对幼虫生存表现并无作用。本研究最终得出结论：成虫能够为子代筛选最优寄主植物，且用于指导产卵决策的化学信号，与调控幼虫生存表现的化学信号并非同一类物质。