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.

植食性昆虫借助植物代谢物甄别寄主植物以完成产卵选择。此类寄主选择行为通常符合偏好-性能假说（Preference-Performance Hypothesis）：雌性个体倾向于在可最大化后代存活与生长性能的寄主植物上产卵。然而，在具有生态相关性的物种互作中，用于指导产卵选择的植物代谢物，以及导致后代性能差异的代谢物，仍未被探明。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*，简称T. mucorea）——开展田间与温室实验，实验所用寄主植物为经转基因改造、次生代谢组分发生特异性改变的植株。两种象甲的雌性成虫均显著偏好取食*Datura wrightii*（简称D. wrightii）而非*Nicotiana attenuata*（简称N. attenuata）的叶片，但烟草象甲倾向于在N. attenuata上产卵，而曼陀罗象甲仅在D. wrightii上产卵。此类产卵行为可提升后代存活性能：曼陀罗象甲幼虫仅能在D. wrightii的茎秆中存活，而烟草象甲幼虫在N. attenuata茎秆中的存活率显著高于其在D. wrightii茎秆中的存活率。利用无尼古丁、茉莉酸（JA，Jasmonic Acid）功能受损以及过表达倍半萜的同基因系N. attenuata植株开展选择实验，结果显示：尽管半数曼陀罗象甲幼虫可在无尼古丁的N. attenuata株系中存活，但尼古丁并未对尼古丁适应性物种与尼古丁敏感物种的产卵行为产生影响。茉莉酸诱导产生的倍半萜挥发性物质是影响烟草象甲雌性成虫产卵选择的关键化合物，但此类倍半萜对幼虫的存活性能并无影响。本研究表明，雌性成虫能够为后代筛选最优寄主植物，且用于指导产卵决策的化学信号与影响幼虫性能的化学信号并非同一类物质。