In recent years, the infestation of Gynaephora qinghaiensis, a lepidopteran pest, has posed significant threats to grassland ecosystems in high-altitude pastoral areas. This pest primarily feeds on valuable forage grasses, leading to reduced pasture quality and potential economic losses in livestock production. Traditional chemical control methods often involve broad-spectrum insecticides, which can cause environmental pollution, harm non-target organisms, and lead to pesticide resistance. To address these challenges, we explored the use of eco-friendly biogenic insecticides applied via crop spraying drones, which offer advantages such as uniform spray distribution, high efficiency, and reduced human exposure. This study aims to screen nine biogenic insecticides for their efficacy against Gynaephora qinghaiensis larvae using a spraying UAV, with a focus on identifying optimal dosages for both emergency and routine control scenarios.
The experiment was conducted in an alpine pasture characterized by a cold, humid climate and diverse vegetation, including grasses and sedges. The area had an average larval density of 56.06 individuals per square meter prior to treatment. We selected nine insecticides, each with three dosage levels, and applied them using a DJI T60 crop spraying drone. This spraying UAV was operated at a flight height of 3 meters and a speed of 5 meters per second, ensuring consistent coverage across the experimental plots. The insecticides included abamectin, azadirachtin, emamectin benzoate·hexaflumuron, nicotine·matrine, pyrethrins·matrine, osthole, lambda-cyhalothrin, Metarhizium anisopliae, and Beauveria bassiana. Each treatment plot covered 1 hectare, with control plots receiving only water. Larval density was assessed before application and at 3, 5, and 7 days post-application using a square meter sampling frame. The corrected control efficacy was calculated to account for natural population changes in control plots.
The corrected control efficacy is defined by the formula: $$ \text{Corrected Control Efficacy} = \frac{\text{Reduction in Treatment} – \text{Reduction in Control}}{1 – \text{Reduction in Control}} \times 100\% $$ where reduction is based on larval density changes. This formula allows for a standardized comparison of insecticide performance. Data were analyzed using ANOVA and Tukey’s HSD test to identify significant differences among treatments.
The results demonstrated varying levels of efficacy among the insecticides over time. For instance, lambda-cyhalothrin and nicotine·matrine showed rapid action, with corrected control efficacies exceeding 90% within 3 days of application. In contrast, fungal-based agents like Metarhizium anisopliae and Beauveria bassiana exhibited delayed but persistent effects, reaching over 80% efficacy by day 7. The table below summarizes the corrected control efficacies for each insecticide at different dosages and time points, highlighting the optimal combinations for effective pest management.
| Insecticide | Dosage (mL/hm² or mg/hm²) | Corrected Efficacy at 3 Days (%) | Corrected Efficacy at 5 Days (%) | Corrected Efficacy at 7 Days (%) |
|---|---|---|---|---|
| Abamectin 5% EC | 150 | 86.1 | 94.2 | 92.2 |
| Abamectin 5% EC | 225 | 87.7 | 94.9 | 94.9 |
| Abamectin 5% EC | 300 | 89.4 | 96.9 | 94.8 |
| Azadirachtin 0.3% EC | 150 | 83.6 | 83.7 | 87.0 |
| Azadirachtin 0.3% EC | 225 | 84.1 | 84.4 | 88.6 |
| Azadirachtin 0.3% EC | 300 | 85.6 | 88.9 | 91.8 |
| Emamectin benzoate·hexaflumuron 6% EC | 150 | 81.3 | 82.2 | 84.9 |
| Emamectin benzoate·hexaflumuron 6% EC | 300 | 83.5 | 83.6 | 86.3 |
| Emamectin benzoate·hexaflumuron 6% EC | 450 | 86.8 | 86.9 | 91.3 |
| Nicotine·matrine 1.2% EC | 225 | 87.1 | 87.5 | 84.7 |
| Nicotine·matrine 1.2% EC | 300 | 90.7 | 88.0 | 90.8 |
| Nicotine·matrine 1.2% EC | 375 | 92.7 | 90.9 | 94.5 |
| Pyrethrins·matrine 0.5% SL | 225 | 84.7 | 90.9 | 89.6 |
| Pyrethrins·matrine 0.5% SL | 300 | 87.7 | 91.6 | 92.2 |
| Pyrethrins·matrine 0.5% SL | 375 | 88.7 | 91.7 | 96.2 |
| Osthole 1% SL | 225 | 78.2 | 81.6 | 89.4 |
| Osthole 1% SL | 300 | 79.6 | 81.5 | 92.9 |
| Osthole 1% SL | 375 | 82.7 | 85.0 | 96.9 |
| Lambda-cyhalothrin 10% EC | 300 | 91.0 | 84.8 | 82.9 |
| Lambda-cyhalothrin 10% EC | 375 | 94.3 | 86.0 | 83.9 |
| Lambda-cyhalothrin 10% EC | 450 | 96.1 | 86.3 | 85.0 |
| Metarhizium anisopliae WP | 600 | 58.1 | 64.9 | 67.0 |
| Metarhizium anisopliae WP | 900 | 60.3 | 69.4 | 72.2 |
| Metarhizium anisopliae WP | 1200 | 65.5 | 73.2 | 80.2 |
| Beauveria bassiana WP | 600 | 58.5 | 67.8 | 70.5 |
| Beauveria bassiana WP | 900 | 60.6 | 75.7 | 79.2 |
| Beauveria bassiana WP | 1200 | 62.8 | 77.0 | 82.4 |
The data indicate that insecticides like lambda-cyhalothrin and nicotine·matrine provide rapid control, making them suitable for emergency situations where pest populations surge abruptly. For instance, at a dosage of 300 mL/hm², both agents achieved over 90% efficacy within 3 days. The mechanisms behind these effects involve neurotoxicity; lambda-cyhalothrin disrupts sodium channels in insect nerves, while nicotine·matrine interferes with acetylcholine receptors. In contrast, agents such as abamectin and fungal-based insecticides showed slower onset but sustained efficacy. Abamectin, for example, targets GABA receptors, leading to paralysis and death, and at 150 mL/hm², it maintained over 90% efficacy by day 5. Fungal insecticides like Metarhizium anisopliae and Beauveria bassiana require more time to infect hosts but offer long-term control, with efficacies reaching 80% or higher at 900 mg/hm² by day 7. This persistence is attributed to their mode of action: they penetrate the insect cuticle, multiply, and produce toxins that compromise the immune system.
Statistical analysis revealed that dosage levels often influenced efficacy, but not always significantly. For example, in abamectin treatments, all dosages produced similar results, whereas in fungal agents, higher dosages (e.g., 900 mg/hm² or 1200 mg/hm²) were more effective. The use of a crop spraying drone ensured precise application, minimizing environmental impact and maximizing coverage. The spraying UAV’s ability to operate at low altitudes with consistent spray patterns is crucial in rugged terrains like alpine pastures. Moreover, the drone’s efficiency reduces labor costs and exposure risks, aligning with sustainable pest management practices. For more details on drone specifications, refer to this resource: UAV Technology in Agriculture.
In terms of economic and environmental considerations, we recommend integrating these insecticides into a rotational program to prevent resistance development. For emergency control, lambda-cyhalothrin 10% EC or nicotine·matrine 1.2% EC at 300 mL/hm² applied via crop spraying drone is optimal. For routine management, alternating abamectin 5% EC (150 mL/hm²), osthole 1% SL (300 mL/hm²), azadirachtin 0.3% EC (300 mL/hm²), pyrethrins·matrine 0.5% SL (300 mL/hm²), emamectin benzoate·hexaflumuron 6% EC (300 mL/hm²), and fungal agents at 900 mg/hm² can provide balanced control. The overall efficacy can be modeled using the equation: $$ E = \frac{\sum_{i=1}^{n} (E_i \times D_i)}{n} $$ where \( E \) is the average efficacy, \( E_i \) is the efficacy of insecticide \( i \), \( D_i \) is its dosage, and \( n \) is the number of insecticides in rotation. This approach ensures sustained pest suppression while minimizing ecological disruption.
In conclusion, the adoption of crop spraying drones for applying biogenic insecticides represents a progressive step in integrated pest management. The spraying UAV technology not only enhances application accuracy but also supports the use of greener alternatives, reducing reliance on conventional chemicals. Future studies should explore longer-term effects and the impact of environmental factors, such as temperature and humidity, on fungal-based insecticides. By leveraging the capabilities of spraying UAVs, we can achieve effective, sustainable control of Gynaephora qinghaiensis in high-altitude grasslands, preserving biodiversity and supporting pastoral economies.