Field assessment of Biopesticides against Bondar’s nesting whitefly (Paraleyrodes bondari peracchi) in coconut ecosystem

Introduction

Coconut (Cocos nucifera L.), belonging to the family Palmae (Arecaceae), is popularly known as the "Kalpavriksha" or divine tree due to its multifaceted utility in nutrition, medicine, cosmetics, and industry. Almost every part of the palm is economically useful, particularly in coconut-growing regions, with major by-products such as tender coconut water, copra, coconut oil, and coir pith contributing substantially to rural livelihoods and the agro-economy. India is the third-largest producer of coconut globally, with an annual production exceeding 21 billion nuts from 2.16 million hectares, recording an average productivity of 21,274 nuts ha⁻¹ (APCC, 2024) [3] . Coconut cultivation is predominantly concentrated in southern India, and Andhra Pradesh alone accounts for 1, 07,370 ha with a productivity of 10,894 nuts ha⁻¹ (CDB, 2024) [4] . With the expansion of global trade, the inadvertent introduction of invasive pests has become a serious challenge to coconut cultivation. Among these, the rugose spiralling whitefly (Aleurodicus rugioperculatus Martin) has emerged as a major invasive pest, first reported from Tamil Nadu and Andhra Pradesh (Sundararaj & Selvaraj, 2016; Chalapathirao et al., 2018) [15,7] . Subsequently, the pest has spread rapidly, causing substantial yield and quality losses. In addition, other whitefly species such as Paraleyrodes spp. have also been reported infesting coconut in Kerala and Karnataka (Josephrajkumar et al., 2019; Vidya et al., 2019) [12, 18] . The increasing incidence of whitefly infestations in coconut and the associated risks of yield loss, environmental contamination, and disruption of natural enemy complexes necessitate the evaluation of biopesticides as sustainable management options. Indiscriminate use of chemical insecticides has led to issues such as pesticide resistance, residue concerns, and adverse effects on non-target organisms, highlighting the need for eco-friendly alternatives. Biopesticides, including entomopathogenic fungi and botanicals, offer target-specific action, compatibility with biological control agents, and reduced environmental footprint. Therefore, systematic evaluation of biopesticides is essential to identify effective, economically viable, and environmentally safe strategies for managing whitefly populations and strengthening integrated pest management (IPM) programs in coconut ecosystems.

Methods of Observation

Evaluation of various biopesticides against the exotic whitefly complex in coconut was undertaken to assess the feasibility of managing the pest using conventional biopesticides. The field experiment was conducted during 2021-22 at HRS, Ambajipeta, following a randomized block design with nine treatments, including an untreated control, and three replications. Each palm constituted one replication. The experiment was carried out on dwarf 'Gauthami Ganga' coconut palms aged 15-20 years. Among the treatments, five were biopesticides, one botanical (azadiractin 10,000 ppm), one jet water spray, and an untreated control. The required quantity of spray solution was prepared freshly at the time of application. Jet water spray was applied using a high-jet sprayer (Honda fourstroke petrol sprayer). Sprays were applied at 15-day intervals. Following the pretreatment count, observations on whitefly population were recorded at 7-day intervals. For population assessment, five palms per treatment were selected randomly. Counts of nymphs, pupae, and adults were recorded from four infested leaflets per leaf taken from four leaves per palm (top, middle, and lower whorls) representing four directions, total of 16 leaflets per palm, and expressed as mean per leaflet/palm. Nymphs and pupae were counted under a Nikon SMZ18 stereomicroscope, while adult populations were recorded visually.

Results and Discussion

BNW Nymphs

As per the data in the table 2, At 7 DAS, Isaria fumosorosea (NBAIR pfu-5 @ 5 ml/L) reduced BNW nymphal population to 6.52 nymphs/leaflet, followed closely by azadiractin 10000 ppm @ 1 ml/L (6.48/ leaflet). Higher populations were recorded in Lecanicillium lecanii (7.38/ leaflet), Beauveria bassiana (6.07/ leaflet), and Metarhizium anisopliae (6.48/ leaflet), while water spray (7.96/ leaflet) and untreated control (9.21/ leaflet) recorded maximum counts.

At 14 DAS, the lowest nymphal population per leaflet was observed in I. fumosorosea (5.59/ leaflet), followed by azadiractin (5.70/ leaflet). Moderate suppression was noted with B. bassiana (5.57/ leaflet), M. anisopliae (6.04/ leaflet), and L. lecanii (6.67/ leaflet). In contrast, water spray (7.

BNW Adults

At 7 DAS, Isaria fumosorosea (NBAIR pfu-5 @ 5 ml/L) recorded the lowest BNW adult population (7.70 adults/ leaflet), followed by azadiractin 10000 ppm @ 1 ml/L (8.59 adults/ leaflet). Comparable adult counts were observed with Lecanicillium lecanii (8.39 adults/ leaflet), Beauveria bassiana (8.36 adults/ leaflet), and Metarhizium anisopliae (8.33 adults/ leaflet). In contrast, water spray (12.84 adults/ leaflet) and untreated control (14.15 adults/ leaflet) recorded significantly higher adult populations as per the data in table 3. At 14 DAS, I. fumosorosea remained most effective with 5.53 adults/ leaflet, followed by azadiractin (6.60 adults/ leaflet). Other biopesticides showed moderate suppression, viz., L. lecanii (6.83 adults/ leaflet), B. bassiana (6.93 adults/ leaflet), and M. anisopliae (7.15 adults/ leaflet). Water spray (12.56 adults/ leaflet) and untreated control (16.52 adults/ leaflet) continued to show higher adult incidence. At 21 DAS, a pronounced decline in adult population was observed in I. fumosorosea (3.40 adults/ leaflet) and azadiractin (4.22 adults/ leaflet), which were significantly superior to other treatments. L. lecanii (4.68 adults/ leaflet), B. bassiana (4.95 adults/ leaflet), and M. anisopliae (5.50 adults/ leaflet) recorded comparatively higher adult numbers, while water spray (12.29 adults/ leaflet) and control (22.74 adults/ leaflet) showed severe infestation. By 28 DAS, I. fumosorosea resulted in the minimum adult population (2.41 adults/ leaflet) with the highest reduction over PTC (80.10%), closely followed by azadiractin (3.24 adults/ leaflet, 78.71% reduction over PTC). L. lecanii (3.72 adults/ leaflet), B. bassiana (4.05 adults/ leaflet), and M. anisopliae (4.65 adults/ leaflet) provided moderate control. Water spray (12.04 adults/ leaflet) was least effective, whereas the untreated control recorded the maximum adult population (28.78), indicating unchecked pest multiplication. Entomopathogenic fungi (EPF) significantly reduced whitefly populations by infecting insect hosts through enzymatic degradation of the cuticle via the production of proteases, chitinases, and lipases, which facilitate conidial attachment and penetration. Among the treatments evaluated, Isaria fumosorosea proved most effective in suppressing whitefly populations compared with Beauveria bassiana, Metarhizium anisopliae and Lecanicillium lecanii, likely due to its superior production of cuticle-degrading enzymes that disrupt host physiological regulation (Ali et al., 2010) [2] . These findings corroborate earlier reports of significant reduction in rugose spiralling whitefly nymphal stages by I. fumosorosea (NBAIR pfu-5) under field conditions (Boopathi et al., 2013) [5] Chalapathirao et al., 2020; Selvaraj et al., 2020) [8,14] . Azadirachtin 10,000 ppm was the next most effective treatment, suppressing all developmental stages of BNW by acting as a growth regulator, antifeedant, and repellent through inhibition of moulting hormone synthesis (Copping and Duke, 2007) [10] , in agreement with earlier reports of reduced RSW adult intensity following azadirachtin application (Chandrika et al., 2017; Alagar et al., 2021) [9,1] . Metarhizium anisopliae was comparatively less effective, possibly due to lower conidial density and poor field persistence, as also reported by Boopathi et al. (2013) [5] .

Conclusion

Among the treatments evaluated, Isaria fumosorosea proved most effective in suppressing BNW nymphal and adult stages compared with other treatments evaluated.

Paraleyrodes bondari

References

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