Efficacy of Biorational Spray Schedules for Sustainable Management of Citrus Thrips (Scirtothrips dorsalis Hood) in Acid Lime
Abstract
Citrus thrips (Scirtothrips dorsalis Hood) is a major constraint in acid lime production, causing leaf distortion, flower drop and severe fruit scarring. Excessive reliance on synthetic insecticides has led to resistance development, residue concerns and disruption of natural enemies. Field experiments were conducted during 2022–23 and 2023–24 at Citrus Research Station, Petlur, Tirupati (Dt), Andhra Pradesh, India to evaluate the efficacy of different biorational insecticide spray schedules against citrus thrips. Eight treatments comprising neem-based botanicals, horticultural mineral oil (HMO), entomopathogenic fungi and Spinosad were evaluated in a randomized block design with three replications. Two sequential sprays were applied at petal fall and pea-size fruit stages. Treatments involving HMO @ 10 ml/lit followed by Spinosad 48 SC @ 0.25 ml/lit and Azadirachtin 1% EC (2 ml/lit) followed by Spinosad 48 SC @ 0.25 ml/lit recorded the lowest thrips population, minimum fruit infestation (3.6–4.1%) and highest yield (20.9–22.4 t/ha) across both seasons. Entomopathogenic fungi provided moderate but significant control, whereas mineral oil alone was less effective under higher pest pressure. The study clearly demonstrates that rotation of biorational insecticides with different modes of action ensures effective suppression of citrus thrips, reduces fruit damage and enhances yield. Such biorational spray schedules offer an environmentally safe, residue-free and sustainable alternative to conventional insecticides and can be effectively integrated into IPM programmes for acid lime cultivation.
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Introduction
Acid lime (Citrus aurantifolia Swingle) is a commercially important citrus species cultivated extensively in southern India, particularly in Andhra Pradesh, where it contributes significantly to farm income and export-oriented horticulture. Productivity and fruit quality in acid lime are severely constrained by insect pests, among which thrips, especially Scirtothrips dorsalis Hood, are considered one of the most economically damaging pests in tropical and subtropical citrus-growing regions (Childers & Achor, 1995; Seal et al., 2006).Both nymphs and adults of S. dorsalis feed on meristematic tissues, including tender leaves, flower buds, and young fruits. Their feeding results in epidermal cell collapse, leading to leaf curling, bronzing, flower drop, and characteristic scab-like fruit scarring, which substantially reduces market acceptability and export value (Childers, 1997; Reddy & Kumar, 2012). Damage occurring during early fruit development is particularly critical, as even low thrips populations can result in severe cosmetic injury and economic loss.Management of S. dorsalis in citrus orchards has largely relied on repeated applications of broad-spectrum synthetic insecticides. However, the pest is highly polyphagous, multivoltine, and capable of rapid population buildup, leading to frequent spray interventions (Seal et al., 2006). Prolonged and indiscriminate use of chemical insecticides has resulted in resistance development, disruption of natural enemy complexes, pest resurgence, and concerns related to pesticide residues on fruits, especially those destined for domestic consumption and export markets (Morse & Hoddle, 2006; Isman, 2006).
In recent years, biorational insecticides have gained considerable attention as environmentally safer alternatives to conventional chemicals. These include botanical insecticides, such as neem-based formulations, and microbial agents, such as entomopathogenic fungi. Azadirachtin, the principal bioactive compound in neem, functions primarily as an insect growth regulator, antifeedant, and oviposition deterrent, thereby suppressing pest populations without causing immediate mortality (Schmutterer, 1990; Isman, 2006). Entomopathogenic fungi such as Beauveria bassiana and Metarhizium anisopliae infect insects through cuticular penetration, leading to systemic mycosis and death, and are generally considered compatible with beneficial arthropods (Shah & Pell, 2003; Vega et al., 2009).Although the efficacy of biorational insecticides against thrips has been demonstrated in vegetable and ornamental cropping systems, their field-level performance in perennial citrus orchards under tropical agroclimatic conditions remains inadequately validated. Moreover, information on optimized spray schedules and rotational use of biorationals for sustainable thrips management in acid lime is scarce. It is hypothesized that sequential application of neem-based formulations and microbial insecticides can effectively suppress S. dorsalis populations, reduce fruit damage, and minimize adverse impacts on natural enemies. In this context, the present study was undertaken to evaluate the efficacy of selected biorational insecticides and their spray schedules against citrus thrips in acid lime. Development of effective biorational-based spray schedules is expected to assist citrus growers in rational pesticide selection, resistance management, improved fruit quality, enhanced export potential, and promotion of sustainable eco-friendly agriculture.
Conclusion
The present study conclusively demonstrated that biorational insecticide spray schedules are effective in managing citrus thrips (Scirtothrips dorsalis Hood) in acid lime when applied at critical crop growth stages. Among the evaluated treatments, T6 (Horticultural Mineral Oil @ 10 ml/lit followed by Spinosad 48 SC @ 0.25 ml/lit) and T1 (Azadirachtin 1% EC @ 2.0 ml/lit followed by Spinosad 48 SC @ 0.25 ml/lit) were found to be the most effective, recording the lowest thrips population, minimum fruit infestation, and highest fruit yield. These treatments were statistically on par with each other and significantly superior to the remaining spray schedules. The study further established that sequential application of biorationals with different modes of action provided prolonged suppression of thrips populations up to 14 days after spraying. Integration of mineral oils or botanical insecticides with Spinosad proved particularly effective in reducing early pest pressure, minimizing fruit scarring, and enhancing marketable yield. Treatments involving entomopathogenic fungi alone showed comparatively lower field efficacy, highlighting the influence of environmental conditions on microbial performance.
Overall, the results emphasize that biorational-based spray rotations can serve as a viable, eco-friendly alternative to conventional insecticides and can be effectively incorporated into Integrated Pest Management (IPM) strategies for sustainable acid lime production.
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