نوع مقاله : علمی - پژوهشی
نویسندگان
1 گروه گیاه پزشکی دانشکده کشاورزی دانشگاه ارومیه
2 1. Department of Plant Protection, Faculty of Agriculture Science, Urmia University, Urmia, Iran
3 Plant Protection Departement, Agriculture Faculty, Urmia University, Urmia, Iran.
چکیده
کلیدواژهها
موضوعات
عنوان مقاله [English]
نویسندگان [English]
Background and objectives: The green oak leaf roller, Tortrix viridana L., is one of the most destructive pests of oak forests. By feeding on developing buds and young foliage, it disrupts photosynthesis, reduces tree growth, causes premature leaf fall, and ultimately leads to the gradual decline of forest stands. In the Zagros forests an ecosystem of exceptional environmental, economic, and historical value recurrent infestations of this pest pose a serious threat to ecosystem sustainability. Due to the limitations associated with chemical insecticides, including environmental hazards, resistance development, and negative impacts on non-target organisms, the application of biological agents and plant-based pesticides within an integrated pest management (IPM) framework has gained increasing attention as a sustainable approach.
Among various biological control agents, entomopathogenic fungi have gained a prominent position due to their active infection process, broad host range, and ability to function under diverse environmental conditions. Lecanicillium lecanii is one of the well-known entomopathogenic fungi, capable of penetrating directly through the insect cuticle, proliferating in the hemolymph, and ultimately killing the host. Additionally, it can reduce feeding and reproductive capacity of insect pests.
On the other hand, botanical insecticides such as Bino2 derived from the roots of Sophora flavescens and rich in active alkaloids (e.g., matrine and sophocarpine) exhibit insecticidal, antifeedant, neurodisruptive, and endocrine-disrupting effects, while offering improved environmental safety compared to conventional chemical pesticides. Combining these biological and botanical control agents may enhance efficacy through synergistic interactions, reduce reliance on synthetic chemicals, and promote long-term sustainability in pest management strategies. Therefore, assessing the compatibility and sublethal impacts of these agents on pest population parameters is an essential prerequisite for developing effective IPM programs.
Methodology: This study aimed to evaluate the compatibility of L. lecanii isolate 229 with Bino2, as well as to investigate the lethal and sublethal effects of each agent alone and in combination against larvae of T. viridana under laboratory conditions. Eggs of the pest were collected from the Pardanan forests of Piranshahr, and third- and fourth-instar larvae were reared under controlled conditions. Bioassays were performed using fungal concentrations ranging from 10⁴ to 10⁸ conidia mL⁻¹, and larval mortality was recorded nine days after treatment. Similarly, Bino2 was tested at graded concentrations based on its recommended field dose, with mortality recorded 24 and 48 hours after treatment. Fungal compatibility was evaluated by measuring conidial germination in media amended with half, equal to, and double the recommended Bino2 dose. Sublethal effects were assessed by treating larvae with LC₂₅ concentrations of each agent alone and combined LC₁₂.₅ + LC₁₂.₅ treatments. Life table parameters including survival, developmental duration, adult longevity, fecundity, and key population growth indices such as intrinsic rate of increase (r), net reproductive rate (R₀), mean generation time (T), and finite rate of increase (λ) were calculated using the two-sex life table method.
Results: Results demonstrated a clear concentration-dependent increase in larval mortality for both agents. The estimated LC₅₀ values of L. lecanii isolate 229 for third- and fourth-instar larvae were 2.01 × 10⁵ and 7.78 × 10⁵ conidia mL⁻¹, respectively. The LC₅₀ values of Bino2 after 48 hours were estimated at 275.50 and 308.09 µL L⁻¹ for third and fourth instars, respectively. Conidial germination exceeded 92% at half the recommended Bino2 dose, indicating no significant inhibition; however, stronger inhibition occurred at the recommended dose, and complete suppression was observed at double the recommended dose, suggesting acceptable compatibility only at lower concentrations.
Sublethal evaluations revealed that LC₂₅ of each agent and the LC₁₂.₅ + LC₁₂.₅ mixture significantly affected the biological performance of the pest. All treatments extended immature developmental duration and reduced adult longevity compared with the control. Reproductive capacity and population growth indices were markedly reduced, with the mixture treatment producing the greatest decrease in intrinsic rate of increase (r) and net reproductive rate (R₀), indicating synergistic suppression of pest population development. Additionally, a significant increase in mean generation time (T) indicated delayed population turnover and slower growth in future generations.
Conclusion: Overall, the findings confirm that L. lecanii 229 and the botanical insecticide Bino2 both possess promising potential for controlling T. viridana, and their combined use at appropriate sublethal levels can enhance efficacy while reducing the required dosage. Given the substantial reductions in pest population growth observed through combined treatments, this strategy may serve as an environmentally sound component of IPM programs targeting the green oak leaf roller. Based on the encouraging laboratory results, field studies are recommended to verify performance and persistence under natural forest conditions.
کلیدواژهها [English]
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