Insecticidal Potential of Defense Metabolites from Ocimum kilimandscharicum against Helicoverpa armigera

Genus Ocimum contains a reservoir of diverse secondary metabolites, which are known for their defense and medicinal value. However, the defense-related metabolites from this genus have not been studied in depth. To gain deeper insight into inducible defense metabolites, we examined the overall biochemical and metabolic changes in Ocimum kilimandscharicum that occurred in response to the feeding of Helicoverpa armigera larvae. Metabolic analysis revealed that the primary and secondary metabolism of local and systemic tissues in O. kilimandscharicum was severely affected following larval infestation. Moreover, levels of specific secondary metabolites like camphor, limonene and β-caryophyllene (known to be involved in defense) significantly increased in leaves upon insect attack. Choice assays conducted by exposing H. armigera larvae on O. kilimandscharicum and tomato leaves, demonstrated that O. kilimandscharicum significantly deters larval feeding. Further, when larvae were fed on O. kilimandscharicum leaves, average body weight decreased and mortality of the larvae increased. Larvae fed on artificial diet supplemented with O. kilimandscharicum leaf extract, camphor, limonene and β-caryophyllene showed growth retardation, increased mortality rates and pupal deformities. Digestive enzymes of H. armigera - namely, amylase, protease and lipase- showed variable patterns after feeding on O. kilimandscharicum, which implies striving of the larvae to attain required nutrition for growth, development and metamorphosis. Evidently, selected metabolites from O. kilimandscharicum possess significant insecticidal activity.罗勒属（Genus Ocimum）蕴含着丰富多样的次生代谢产物，这类物质以其防御功能与药用价值闻名。然而，目前学界对该属植物中与防御相关的代谢产物尚缺乏深入研究。为更深入地探究诱导型防御代谢产物，我们针对吉马桑罗勒（Ocimum kilimandscharicum）在受到棉铃虫（Helicoverpa armigera）幼虫取食后的整体生化与代谢变化展开了分析。代谢分析结果显示，经幼虫侵染后，吉马桑罗勒局部与系统组织的初生及次生代谢均受到严重影响。此外，在昆虫侵袭后，叶片中樟脑（camphor）、柠檬烯（limonene）与β-石竹烯（β-caryophyllene）等已知具备防御功能的特定次生代谢产物水平显著升高。我们将棉铃虫幼虫同时暴露于吉马桑罗勒与番茄叶片的取食选择试验表明，吉马桑罗勒可显著抑制幼虫取食行为。进一步研究发现，以吉马桑罗勒叶片为食的幼虫，其平均体重出现下降，且幼虫死亡率上升。在添加了吉马桑罗勒叶片提取物、樟脑、柠檬烯与β-石竹烯的人工饲料中饲养的幼虫，表现出生长迟缓、死亡率升高以及蛹畸形等症状。取食吉马桑罗勒后，棉铃虫的消化酶——即淀粉酶、蛋白酶与脂肪酶——呈现出不同的活性变化模式，这表明幼虫为满足生长、发育与变态所需的营养需求，正进行着适应性的代谢调节。综上可见，吉马桑罗勒中的特定代谢产物具备显著的杀虫活性。