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.

植食性昆虫会借助植物代谢物甄别寄主植物以完成产卵选择。这类寄主选择行为通常符合偏好-表现假说（preference–performance hypothesis）：雌性成虫会将卵产在最利于后代存活表现的寄主上。然而，在具有生态相关性的物种互作体系中，用于指导产卵选择的代谢物，以及导致后代表现差异的代谢物，仍未被探明。本研究通过田间与温室实验，利用次生代谢不同组分被特异性改造的转基因寄主植物，探究了两种同域分布象鼻虫——曼陀罗象鼻虫（Trichobaris compacta）与烟草象鼻虫（T. mucorea）的寄主选择行为。两种象鼻虫的雌性成虫均显著偏好取食莱特曼陀罗（Datura wrightii）叶片，而非渐狭烟草（Nicotiana attenuata）叶片；但烟草象鼻虫更倾向于在渐狭烟草上产卵，而曼陀罗象鼻虫仅会将卵产在莱特曼陀罗上。这类产卵行为提升了后代的存活表现：曼陀罗象鼻虫幼虫仅能在莱特曼陀罗的茎秆中存活，而烟草象鼻虫幼虫在渐狭烟草茎秆中的存活率显著高于其在莱特曼陀罗茎秆中的存活率。针对无尼古丁、茉莉酸（Jasmonic acid, JA）功能受损以及过量合成倍半萜的同基因渐狭烟草植株开展的选择实验显示：尽管约半数曼陀罗象鼻虫幼虫可在无尼古丁的渐狭烟草品系中存活，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物是影响烟草象鼻虫雌性成虫产卵选择的关键化合物，但这类倍半萜对幼虫的存活表现并无影响。本研究结论表明，雌性成虫能够为后代选择最优寄主植物，且其用于指导产卵决策的化学信号，与影响幼虫存活表现的化学信号并非同一类物质。