Biocontrol potential of aqueous and methanolic extracts of Russian knapweed, Acroptilon repens, L. (Asteraceae) against Trialeurodes vaporariorum (Hemiptera: Aleyrodidae)

Plant based natural products could be used as new alternative of chemical insecticides due to their co-friendly, safety to non-target organisms, and low-level resistance properties. In this study, the contact toxicity and sublethal effects of Acroptilon repens L., Russian knap weed, extracts (aqueous and methanolic) were evaluated on the biological, population traits and population projection of greenhouse whitefly, Trialeurodes vaporariorum. The essential oil was extracted from the plant by steam distillation using a Clevenger apparatus and the chemical compounds were identified by gas chromatography-mass spectrometry. Twenty-three chemical components of A. repens were characterized, in which caryophyllene oxide (30.67%) and α-copaene (15.05%), were identified as the predominant compounds of Russian knapweed. Moreover, the results illustrated that some secondary metabolites (e.g. flavonoids, alkaloids and polyphenols) were rich in methanolic extract compared to the control. The leaf dipping method was used for the bioassay tests against whiteflies. According our findings, the aqueous extract (LC₅₀: 1802.59 ppm) was more toxic than the methnolic treatment (LC₅₀: 3849.15 ppm) on the T. vaporariorum adults. The age-stage, two-sex life table theory was used to analyze the life table data. The sublethal concentration of either aqueous or mehanolic extracts of A. repens significantly affected the biological and population growth parameters of T. vaporariorum compared to the control by prolongation the developmental period, adult longevity, reducing the survival rate, fecundity and decreasing the net reproductive rate (R₀), intrinsic rate of increase (r), and finite rate of increase (λ) of adults, as well. The overall results demonstrated that both of the Russian knapweed extracts could be considered in management programs of greenhouse whitefly. However, the cost-effective property of aqueous extract should not be neglected.