Influence of Water pH on Insecticide Efficacy against Pectinophora gossypiella (Lepidoptera: Gelechiidae) under Field Conditions

The pink bollworm, Pectinophora gossypiella (Saunders) (Lepidoptera: Gelechiidae) is one of the key pests of cotton in the world. Farmers often use insecticides to control this pest, but various factors impact their effectiveness, with water quality being one of the most important yet frequently neglected. Using impure water as a solvent can significantly decrease insecticide performance due to unfavourable pH levels. To address this critical issue and the significant research gap, this study was conducted to evaluate the impact of water pH on the performance of synthetic and bio-insecticides. A field experiment was conducted using cotton variety Sindh-1. Various synthetics (Novaluron, Chlorantraniliprole, Emamectin benzoate, and Gamma-Cyhalothrin) and botanical insecticides (Azadirachta indica, Eucalyptus globulus, Calotropis procera, and Datura stramoniums) were screened for their effectiveness against P. gossypiella. Both synthetic and botanicals insecticides were dissolved with various water pH levels (4-10). All insecticides were applied at their recommended dose and data was recorded before spray, whereas subsequent observations were taken after 24, 48, 72, 96, and 168 hours of the spray. There were a total of two sprays that were done at 15 days interval. Five plants were randomly selected to record infestation of P. gossypiella from flowers, buds, twigs, and bolls. ANOVA with LSD and Correlation co-efficient were analyzed through statistical software Statistix 8.1. The results further revealed that all applied synthetic insecticides were more effective than the botanical treatments. However, among the applied botanicals, Azadirachta indica (2.00±0.19 and 1.95±0.13 larvae/plant) gave the maximum reduction in the P. gossypiella population, followed by E. globulus powder (2.20±0.17 and 2.00±0.11 larvae/plant), observed 24 hours after the first and second sprays with pH5 water, followed by pH6 water treatment, respectively, while D. stramonium and C. procera were the least effective among the botanicals. The highest corrected infestation reduction in P. gossypiella was recorded with Novaluron (83.33±0.14% and 83.12±0.14% in the first and second sprays, respectively) at 96 hours when applied with pH 7 water. In contrast, Chlorantraniliprole showed maximum reduction (71.88±0.14% and 73.40±0.14%) at 96 hours when applied with pH 6 water. However, among the applied botanicals the A. indica gave maximum reduction in P. gossypiella infestation (58.33±0.12 and 56.38±0.12 %) after first and second spray at 96 hours of application, respectively. Keeping in view the above findings, it is suggested that the application of Novaluron or Chlorantraniliprole, mixed with pH 7 and pH 6 water can be done to reduce the infestation of P. gossypiella, whereas Azadirachta indica can also be a good substitute of the synthetic insecticide for P. gossypiella to lower environmental pollution and resistance development in the pest.