Efficacy of Entomopathogenic fungi and botanicals against Rugose spiralling whitefly, Aleurodicus rugioperculatus martin in coconut under low grade (spirals

Introduction

The coconut palm (Cocos nucifera L.), a prominent member of the family Arecaceae (Palmae), is widely recognized for its immense economic, nutritional, medicinal, and industrial value and is aptly referred to as the "Kalpavriksha." India is one of the leading coconut-producing countries, with cultivation predominantly concentrated in the southern states, where the crop plays a vital role in sustaining rural livelihoods and the national agroeconomy (APCC, 2024; CDB, 2024) [4,8] . However, coconut cultivation is severely constrained by a wide range of insect pests, among which invasive whiteflies have emerged as a major threat in recent years, causing significant yield losses due to sap sucking, honeydew excretion, and subsequent sooty mould development that interferes with photosynthesis (Francis et al., 2016) [14] . The intensification of global agricultural trade has facilitated the accidental introduction and rapid spread of invasive pests such as the rugose spiralling whitefly (Aleurodicus rugioperculatus) in coconut ecosystems across India (Ananthakrishnan, 2009; Sundararaj and Selvaraj, 2017; Chalapathirao et al., 2018) [3,22,9] . These pests have proliferated rapidly due to their polyphagous nature, cryptic life stages, and favourable climatic conditions, often in the absence of effective native natural enemies (Simala et al., 2015; Srinivasan et al., In this context, biological control using biopesticides offers a promising, environmentally safe alternative to conventional chemical pesticides. Entomopathogenic fungi such as Beauveria bassiana, Metarhizium anisopliae, Lecanicillium lecanii, and Isaria fumosorosea have gained considerable attention due to their host specificity, safety to non-target organisms, and compatibility with natural enemies (Ali et al., 2010) [2] . These biopesticides infect insect hosts through cuticular penetration and internal colonization, leading to effective suppression of pest populations without leaving harmful residues or inducing resistance. Given the increasing incidence of invasive whitefly complexes and the drawbacks associated with chemicalbased control measures, systematic evaluation of biopesticides under field conditions is essential. Assessing their efficacy against different life stages of whiteflies and their interaction with natural enemy complexes will aid in identifying sustainable and eco-friendly management strategies (Boopathi et al., 2013; Selvaraj et al., 2020) [6,18] . Such evaluations are crucial for strengthening integrated pest management (IPM) programmes, reducing chemical dependence, and ensuring long-term sustainability of coconut production systems.

Methods of observation

The field experiment was conducted at Horticultural Research Station (HRS), Ambajipeta during 2021-2022 to evaluate the efficacy of different biopesticides against RSW in coconut. The experiment was laid out in a Randomized Block Design (RBD) with nine treatments and five replications. Coconut palms were planted at a spacing of 7.5 × 7.5 m and the variety 'Gauthami Ganga' was selected for the study. Among the treatments, six 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).

Table 1: List of various bio-pesticides evaluated against whitefly complex.

Treatments Concentration Dosage T1

Isaria fumosorosea NBAIR pfu-5 @ 5 ml/L 1 X 10 Control (no spraying) --

In the coconut plantation, spray applications were carried out at 15-day intervals. After recording the pre-treatment counts, observations on whitefly populations were made at 7 day intervals following each spray. For population assessment, five coconut palms per treatment were selected randomly. Counts of nymphs, pupae, and adults were recorded from four pest-infested leaflets per leaf, collected from four leaves per palm representing the top, middle, and lower whorls and all four directions, total of 16 leaflets per palm. The observations were expressed as mean population per leaflet per palm. Nymphs and pupae were counted under a Nikon SMZ18 stereomicroscope, while adult whiteflies were recorded through visual observation. The pest population reduction is obtained by using following formula [19]

Results and Discussion Evaluation of biopesticides against RSW (A. rugioperculatus) life stages under low grade (> 10 spirals/ leaflet).

The categorization of low, medium and high grade was exclusively based on the number of spirals/ leaflet irrespective of the nymph, pupae and adult stages of whitefly complex.

As per the rating scale given by Selvaraj et al. (2016) [19] , the RSW spirals under field conditions were less than 10 numbers (grade -low incidence) were used for the study. The data on efficiency of biopesticides in reducing the pest population viz., egg spirals, nymphs, pupae and adults are furnished in the below heads.

RSW Spirals

The overall results revealed that, significant difference was observed among different treatments of bio pesticides against spirals and webs at 7, 14, 21 and 28 days after spraying (DAS). The treatment I. fumosorosea NBAIR pfu-5 @ 5 ml/L recorded highest spiral reduction of 91.05% and was found to be superior followed by Azadirachtin 10, 000 ppm @ 1 ml/ L with reduction of 88.02% after 28 DAS. Among the other entomopathogenic fungi, evaluated C. perangustum and F. equiseti were found to be promising with reduction of 85.44% and 81.77% after 28 DAS (Table 3).

RSW Nymphs.

I. fumosorosea NBAIR pfu-5 @ 5 ml/L was found to be effective in reducing the nymphal population of RSW with 82.00% reduction after 28 DAS followed by Azadirachtin 10, 000 ppm @ 1 ml/L with reduction of 78.71%. Among the other entomopathogenic fungi evaluated, C. perangustum was found to be promising in reducing the nymphs with reduction 73.38% after 28 DAS. F. equiseti was found to be promising in reducing nymphs of RSW with reduction 71.20% after 28 DAS. However, the control treatment recorded highest population of nymphs of both RSW with 50.67/leaflet (Table 4).

RSW Pupae

The overall results revealed that there was existence of significant difference among different treatments against RSW. Least number of pupae were recorded in treatment I. fumosorosea NBAIR pfu-5 @ 5 ml/L with 76.73% reduction over PTC RSW pupae after spraying and proved to be superior compared to that of other treatments followed by Azadirachtin 10, 000 ppm @ 1 ml/L with 73.29% reduction. The control treatment was recorded with highest population of 43.62 pupae/ leaflet after 28 DAS. M. anisopliae @ 5 ml/L was found to be least effective in reducing the pupal population of RSW as per the data presented in (Table 5).

RSW Adults

The overall results during the experiment indicated that, significant difference was observed among different treatments against adults of RSW. I. fumosorosea NBAIR pfu-5 @ 5 ml/L recorded lowest number with 91.97% reduction of RSW after spraying and found to be promising followed by Azadirachtin 10, 000 ppm @ 1 ml/L (T2) with reduction of 90.40%. Among the treated biopesticides M. anisopliae had least effect on adult population with 72.67% reduction of RSW adults after 28 days. The control (untreated) was recorded with highest population of both RSW adults with 42.10 after 28 days (Table 6). The present investigation clearly demonstrated that foliar application of entomopathogenic fungi (EPF) substantially reduced the population of spirals, webbing, nymphs, pupae, and adults of both rugose spiralling whitefly (RSW). During the infection process, EPF secrete a complex of extracellular enzymes such as proteases, chitinases, and lipases, which facilitate degradation of the insect cuticle and enhance adhesion, germination, and penetration of fungal conidia into the host body. Among the evaluated treatments, Isaria fumosorosea proved to be the most effective in suppressing all life stages of Aleurodicus rugioperculatus, including spirals, nymphs, pupae, and adults. Its performance was markedly superior to that of Beauveria bassiana, Metarhizium anisopliae, Cladosporium perangustum, Fusarium equiseti, and Lecanicillium lecanii, resulting in a significant reduction in pest incidence and intensity in coconut plantations. The higher efficacy of I. fumosorosea can be attributed to its ability to produce hydrolytic enzymes such as chitinase, chitosanase, and lipase, which enable physical penetration of the insect cuticle and effective disruption of the host's physiological and regulatory systems (Ali et al., 2010) [2] . The present findings are in close conformity with the reports of Boopathi et al. (2013, 2015) [6,7] and Chalapathirao et al. (2020) [10] , who documented that I. fumosorosea NBAIR pfu-5 reduced early nymphal instars of RSW by 52-68% and 35-40% in Godavari Ganga hybrid and Gauthami Ganga coconut varieties, respectively. Further support to the present results is provided by Selvaraj et al. (2020) [18] , who identified I. fumosorosea NBAIR pfu-5 as a promising strain for managing RSW populations in coconut and oil palm ecosystems of Karnataka and Andhra Pradesh through two spray applications at 15-day intervals. Similarly, Visalakshi et al. (2021) [23] reported a reduction of 58.10 to 97.03% in RSW intensity on coconut palms treated with I. fumosorosea (NBAIR pfu-5) @ 2 × 10⁸ spores ml⁻¹ (5 g L⁻¹ of water). Although Pradhan et al. (2020) observed 100% mortality of whiteflies following I. fumosorosea application, complete mortality was not recorded under the present field conditions, possibly due to environmental and host-related factors influencing fungal performance. Sumalatha et al. (2020) [18] further demonstrated that among the two strains of I. fumosorosea (ICAR-NBAIR pfu-1 and pfu-5), only the pfu-5 strain exhibited virulence against RSW. The pfu-5 strain induced mean mortalities of 44.03%, 44.80%, 36.42%, and 28.82% in eggs, first, third, and fourth instar nymphs, respectively, reinforcing its potential as an effective biocontrol agent. Azadirachtin 10, 000 ppm emerged as the next most effective treatment after I. fumosorosea, significantly suppressing all developmental stages of both RSW. Azadirachtin interferes with insect growth and development by inhibiting ecdysone-20-monooxygenase activity in the haemolymph, thereby preventing the conversion of ecdysone into its active moulting hormone, 20hydroxyecdysone. Consequently, it functions as a potent growth regulator, antifeedant, and repellent against a wide range of phytophagous insects (Copping and Duke, 2007) [12] . The bioactive limonoid triterpenoid nature of azadirachtin affects digestive, endocrine, and reproductive systems of insects and induces strong antifeedant responses. The present findings corroborate earlier reports by Chandrika et al. (2017) [11] , Elango and Jayarajan (2020) [13] , Alagar et al. (2021) [1] , and Krishnarao and Chalapathirao (2019), who recorded significantly lower adult intensity of RSW following azadirachtin 10, 000 ppm application. Cladosporium perangustum exhibited moderate efficacy in reducing nymphal and adult populations of both RSW. Species of Cladosporium are known to act as insect pathogenic microorganisms, and ethyl acetate extracts derived from C. cladosporioides have been reported to be effective against nymphs and adults of cotton aphid, Aphis gossypii (Omar et al., 2019) [16] . Similar trends of moderate suppression were observed in the present study, indicating its potential role as a supplementary biocontrol agent. In contrast, Metarhizium anisopliae failed to provide satisfactory control of RSW under field conditions. Its relatively poor performance may be attributed to lower conidial density, reduced persistence, or suboptimal environmental compatibility, which limited its ability to suppress pest populations effectively. Comparable observations were earlier reported by Boopathi et al. (2013) [6] , who also recorded reduced field efficacy of M. anisopliae against RSW.

Conclusion

Among the treated biopesticides Isaria fumosorosea NBAIR pfu-5 @ 5 ml/L water was found to be superior in reducing the RSW population followed by Azadirachtin 10, 000 ppm @1 ml/ L water. In contrast, Metarhizium anisopliae was found to be least effective in reducing the pest population.

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