Sublethal Effects and Biological Parameters of the Botanical Insecticides Matrine and Neemarin on the Green Oak Tortrix, Tortrix viridana L.

Introduction and Objective: Oak trees are considered keystone species in the Zagros forests, playing a critical role in environmental stability, soil conservation, and biodiversity. However, the ecological integrity of these ecosystems is increasingly threatened by leaf-feeding pests. Among them, the green oak tortrix (Tortrix viridana L.) is a major defoliator that feeds on vegetative and reproductive buds, flower clusters, and young leaves, leading to premature defoliation, disrupted photosynthesis, and reduced regeneration in oak stands. This univoltine pest poses a serious challenge to forest health. In recent years, botanical insecticides such as Neemarin (derived from Azadirachta indica A. Juss) and Matrine (extracted from Sophora flavescens Ait.) have gained attention as eco-friendly alternatives to synthetic chemicals. These compounds exert both lethal and sublethal effects, including reduced fecundity, developmental disruption, and feeding deterrence. Although their efficacy has been documented in several pest species, there is a lack of direct evidence regarding their impact on T. viridana.
Materials and Methods: Third instar larvae of T. viridana were collected from oak forests in Piranshahr at West Azerbaijan Province and reared under laboratory conditions on fresh leaves of Quercus infectoria G. Olivier. The insecticidal activity of Matrine and Neemarin was assessed using five concentrations and a control. Oak leaves were dipped in each solution for 5 seconds, air-dried, and placed in 9-cm Petri dishes covered with organza mesh. Ten larvae were added per dish and maintained at 25 ± 2 °C and 65 ± 5% RH. Mortality was assessed after 48 hours using a heated needle method. For sublethal assays, larvae were exposed to LC20 concentrations of each insecticide for 5 seconds, then transferred to untreated leaf discs. Life history traits including longevity, pupation rate, fecundity, and daily egg production were recorded. Data were analyzed using probit analysis (SPSS), two-sex life table software (TwoSex-MSChart), and SigmaPlot for visualization. Life table parameters were compared using the paired bootstrap method.
Results: Lethal concentration values LC50 and LC20 were calculated for both botanical insecticides. The LC50 and LC20 for Matrine were 80.23 and 29.20 µL/mL, respectively, while those for Neemarin were 243.21 and 86.04 µL/mL, indicating higher toxicity of Matrine. Adult longevity significantly decreased under both treatments: 8.84 days (Matrine), 10.85 days (Neemarin), and 13.40 days (control). The oviposition period was reduced from 11.48 days (control) to 6.35 days (Matrine) and 8.95 days (Neemarin). Sublethal exposure caused significant reductions in fecundity. Key population parameters such as net reproductive rate (R0), intrinsic rate of increase (rm), and gross reproductive rate (GRR) showed significant declines in treated groups compared to the control. The age-stage specific life expectancy (exj) of the first female decreased from 17.03 days (control) to 14.18 (Neemarin) and 12.05 days (Matrine). Reproductive value (vxj) also declined after exposure to sublethal doses, reflecting reduced fecundity and survival, and dropped to zero post-oviposition.
Conclusion: This study demonstrates that Matrine and Neemarin possess both lethal and sublethal activity against T. viridana larvae. These botanical insecticides significantly impacted developmental time, survival, fecundity, and key demographic parameters. Given their efficacy and eco-safety, they offer promising potential for inclusion in integrated pest management (IPM) programs targeting oak defoliators in sensitive ecosystems such as the Zagros forests. Their use may contribute to reducing reliance on synthetic chemicals, preserving beneficial organisms, and enhancing ecological sustainability.