Department of Biology, University of Colorado Colorado Springs, 1420 Austin Bluffs Parkway, Colorado Springs, CO 80907, USA.
Colorado Natural Heritage Program, Colorado State University, Fort Collins, CO, USA.
Environ Entomol. 2023 Dec 15;52(6):1082-1094. doi: 10.1093/ee/nvad107.
Host-plant phenology can directly and indirectly mediate the abundance of insect herbivores. Our objective was to determine how host-plant flowering phenology shapes a facultative ant-lycaenid mutualism. The focus of our research was the hops azure, Celastrina humulus Scott & D. Wright, a rare species whose larvae feed on the pollen-bearing inflorescences of Humulus lupulus var. neomexicanus. We used several approaches to evaluate the role of host-plant flowering phenology in this system. First, we monitored larvae over three study years (2020-2022) to parse the role of host-plant flowering phenology and other factors in shaping the likelihood of ant tending. Second, we tested larval performance at various phenological stages of the host plant. We also quantified variation in soluble proteins and secondary metabolites among inflorescences at varying phenological stages. Lastly, we treated artificial sugar-protein baits with extracts from different phenological stages of the host plant; this allowed us to assess how chemical variation among stages could impact ant recruitment. Monitoring results revealed that the likelihood of ant tending was lowest for larvae on host plants with early-stage inflorescences. These floral stages had the greatest concentrations of both soluble proteins and α-acids (humulone and cohumulone), and in the feeding trial, early-stage flowers enabled greater weight gain for larvae. However, extracts from early-stage flowers reduced ant recruitment to sugar-protein baits. Altogether, these results suggest that early-stage inflorescences enhance larval growth while also reducing the recruitment of mutualist ants. This shows an indirect mechanism whereby changing host-plant phenology can mediate herbivore populations through interactions with ants.
植物物候可以直接和间接调节昆虫食草动物的丰度。我们的目标是确定植物物候如何塑造一种兼性蚂蚁-蓝闪蝶共生关系。我们研究的重点是啤酒花天蓝 Celastrina humulus Scott & D. Wright，这是一种稀有种，其幼虫以 Humulus lupulus var. neomexicanus 的花粉状花序为食。我们使用了几种方法来评估植物物候在这个系统中的作用。首先，我们在三个研究年（2020-2022 年）监测幼虫，以解析植物物候和其他因素在塑造蚂蚁倾向可能性方面的作用。其次，我们测试了幼虫在宿主植物不同物候阶段的表现。我们还量化了不同物候阶段花序中可溶性蛋白质和次生代谢物的变化。最后，我们用来自宿主植物不同物候阶段的提取物处理人工糖-蛋白诱饵；这使我们能够评估不同阶段之间的化学变化如何影响蚂蚁的招募。监测结果表明，在早期花序上的幼虫蚂蚁倾向的可能性最低。这些花阶段含有最多的可溶性蛋白质和α-酸（葎草酮和副葎草酮），在喂养试验中，早期的花使幼虫体重增加更多。然而，早期花的提取物减少了糖-蛋白诱饵对蚂蚁的招募。总之，这些结果表明，早期的花序增强了幼虫的生长，同时减少了共生蚂蚁的招募。这表明一种间接机制，即通过与蚂蚁的相互作用，改变宿主植物物候可以调节食草动物的种群。
