Toxicity of Delphinium brunonianum Royle alkaloids against the adults of Diaphorina citri and its mechanism study in insect SF9 cell line

Globally, the agriculture sector massively relies on synthetic chemical pesticides for pest management, and the extensive use of these synthetic chemicals poses a severe threat to humans and the environment. Therefore, due to their environmental friendliness, new crop protection strategies, including botanical pesticides, have gained attention over the past decades. In the Skardu Baltistan, Pakistan, annually, tons of Delphinium brunonianum are wasted due to not being used economically. Therefore, the current study aims to investigate the toxicity of D. brunonianum as a novel pesticide for managing Diaphorina citri, one of the world’s most destructive pests of citrus species. From the most active fraction of D. brunonianum that showed toxicity against D. citri, we have isolated and identified four alkaloids: delpheline, delbrunine, eldeline, and delsoline. The results indicated that D. brunonianum alkaloid extract (DBAE) and its isolated alkaloids caused significant acute mortalities against D. citri in topical and residual contact methods. However, the toxicity of DBAE was stronger than the isolated alkaloids with LD50 and LC50 values of 0.26 μg/insect and 76.56 μg/mL. Among the isolated alkaloids, eldeline, delsoline, and delbrunine were toxic, with LD50 values of 0.48, 0.52, and 0.97 μg/insect applied topically and LC50 values of 96.72, 98.43, and 124.57 μg/mL in residual contact method. Furthermore, to understand the toxicity mechanism of DBAE and its isolated alkaloids, the ovarian cell line of Spodoptera frugiperda (SF9) was used as a model. The result of cell viability, DNA fragmentation, and morphological changes in treated SF9 cells indicated that DBAE and its isolated alkaloids inhibit cell proliferation and induced apoptosis and thus exert insecticidal effects. Therefore, it has been concluded that DBAE and its isolated alkaloids have the potential to be developed as a novel alternative to synthetic insecticides for the management of D. citri.