Laboratory toxicity assessment of five biopesticides on Conopomorpha sinensis Bradley

This study aimed to explore the feasibility of using biopesticides to control Conopomorpha sinensis Bradley, a major pest of Litchi chinensis Sonn., as an alternative to chemical pesticides, addressing issues related to pesticide residues in the litchi industry.

Laboratory toxicity assays were conducted to evaluate the insecticidal activity of five biopesticides—rotenone, matrine, cinnamaldehyde, spinosad, and spinetoram—against both adult and egg stages of C. sinensis.

The results showed that cinnamaldehyde, spinosad, and spinetoram exhibited the highest efficacy, achieving 100% corrected mortality of adults within 48 hours. Although rotenone exhibited a slower onset of action, its corrected mortality rate also approached 100% after 72 hours. Matrine exhibited the weakest toxicity. In egg hatching inhibition assays, cinnamaldehyde demonstrated the highest corrected hatching inhibition rate (84.00 ± 4.00)%, significantly higher than matrine ((32.00 ± 8.00)%, P < 0.05). However, cinnamaldehyde's efficacy was not significantly different (P < 0.05) from spinetoram (76.00 ± 6.93)%, spinosad (60.00 ± 8.00)%, or rotenone (52.00 ± 18.33)%. Toxicity regression analysis further validated that cinnamaldehyde had the lowest LC₅₀ value (0.060 mg/L) for adults, indicating the highest toxicity. Spinosad (LC₅₀ = 19.570 mg/L) and spinetoram (LC₅₀ = 24.119 mg/L) followed. Cinnamaldehyde also showedthe highest toxicity for egg hatching inhibition, with the lowest LC₅₀ value (0.045 mg/L), significantly lower than those of spinosad (30.867 mg/L) and spinetoram (12.406 mg/L).

Overall, cinnamaldehyde demonstrated high toxicity against both life stages of C. sinensis, supporting its use as a preferred biopesticide, with spinosad and spinetoram serving as effective alternatives. These findings provide a scientific basis for environmentally friendly management of C. sinensis and contribute to sustainable litchi production.