DISSERTATION RESEARCH: Defensive chemistry underlying latitudinal patterns in plant-herbivore interactions

农作物病虫害在各地的分布并不总是恒定的。如果科学家能够预测何时何地虫害最严重，就可以防止经济损失。该项目将提供对环境(气候、夏季长度等)的具体作用的直接洞察。在虫害压力上。研究人员将在野生植物物种而不是农作物物种中解决这个问题。这是因为农药和农业实践掩盖了自然因素的影响。这项研究的重点物种是商陆(及其相关害虫)。商陆是原产于美国东部的一种具有重要文化意义的多年生植物。先前的研究表明，在美国南部和北部，美洲商陆被毛虫大量吃掉。这项提议检查了商陆对昆虫的防御能力是否在南方更强。这种模式表明，南方的植物已经适应了较强虫害压力的长期历史。此外，这项研究还将回答有关环境如何影响植物和昆虫之间关系的基本问题。这也将有助于解开长期存在的谜团，即为什么更接近赤道的生态系统比更高纬度的生态系统拥有更多的物种。该项目还将通过制作关于纬度多样性的视频分发给教师来加强K-12教育。该项目检验了低纬度地区植物得到更好化学保护的假设。研究人员将使用一种多才多艺的毛虫(甜菜夜蛾)来进行生物防御测试，并将毛虫的表现与树叶特征联系起来。初步试验表明，以低纬度植物的商陆叶片饲养的甜菜夜蛾的死亡率高于高纬度植物的死亡率，这表明低纬度植物的防御能力更强。纬度较低的树叶更坚韧，所以为了分离机械和化学防御特性，研磨的树叶将被加入琼脂中进行生物测试，只测试化学防御的效果。液质联用仪和气质联用仪将表征叶片的化学组成，碳氮比将作为叶片营养价值的指标。总而言之，该项目提出了哪些树叶性状可以预测毛虫在纬度梯度上的表现，促进了我们对植物防御中的地理差异的理解，并解决了最近关于较低纬度地区更强的生物相互作用的普遍性的争议。

The distribution of crop pests is not constant in all places always. If scientists could predict where or when pests would be worst, it could prevent financial losses. This project will provide direct insight into the specific role of the environment (climate, summer length, etc.) on pest pressure. The researchers will address this question in a wild plant species rather than a crop species. This is because pesticides and agricultural practices hide the influence of natural factors. The focal species in this study is pokeweed (and associated pests). Pokeweed is a culturally significant perennial plant native to the eastern USA. Prior research has shown that pokeweed is heavily eaten by caterpillars in the southern vs. northern US. This proposal checks if pokeweed's defenses against insects are stronger in the South. That pattern would suggest that the plants in the South have adapted to a long history of stronger pest pressure. In addition, the research will answer basic questions about how the environment influences relationships between plants and insects. It will also help to address the long-standing mystery of why ecosystems closer to the equator have more species than ecosystems at higher latitudes. The project will also enhance K-12 education through the creation of videos on latitudinal diversity for distribution to teachers.This project tests the hypothesis that plants are better chemically defended at lower latitudes. The researchers will use a generalist caterpillar (Spodoptera exigua) to bioassay defense, and correlate caterpillar performance with leaf traits. Preliminary trials show that mortality is greater for S. exigua raised on a diet of pokeweed leaves from lower vs. higher latitude plants, suggesting that low-latitude plants are better defended. Lower latitude leaves are tougher, so to disentangle mechanical and chemical defense traits, ground leaves will be incorporated into agar for bioassays that test the effects of chemical defenses only. Liquid and Gas Chromatography Mass Spectrometry will characterize leaf chemistry profiles, and the ratio of carbon to nitrogen will serve as an index of leaf nutritional value. In sum, the project asks which leaf traits predict caterpillar performance over a latitudinal gradient, advancing our understanding of geographic variation in plant defense and addressing recent controversy about the generality of stronger biotic interactions at lower latitudes.