Lethal and sub-lethal effects of fipronil on growth and development of okra shoot and fruit borer (Earias vitella: Noctuidae: Lepidoptera)

Abstract

The shoot and fruit borer Earias vitella (Fabricius) is a major pest affecting okra (Abelmoschus esculentus), causing significant yield and quality losses across all crop stages. Chemical control remains a primary strategy, with fipronil, a phenyl pyrazole insecticide, being widely used. This study evaluated the lethal (LC₅₀) and sub-lethal (LC₁₅ and LC₁₀) effects of fipronil on the growth and development of E. vitella under laboratory conditions at ICAR-IIVR, Varanasi, using diet incorporation bioassays. The LC₅₀ value was determined to be 4.844 ppm, while LC₁₅ and LC₁₀ were 0.068 ppm and 0.025 ppm, respectively. Sub-lethal doses significantly influenced key biological parameters, including prolonged larval and pupal durations, reduced larval and pupal weight and length, increased mortality, reduced pupation and adult emergence rates, and decreased fecundity. Growth index and adult longevity were also notably reduced compared to the control. These findings suggest that, beyond direct lethality, sub-lethal exposures to fipronil can impair developmental and reproductive fitness in E. vitella, potentially offering extended pest suppression benefits. The study highlights the importance of incorporating sub-lethal effects into insecticide efficacy assessments for integrated pest management (IPM) strategies in okra cultivation.