Seasonal incidence of major insect pests and their association with weather parameters in watermelon (Citrullus lanatus L.)

Introduction

Watermelon (Citrullus lanatus Thunb. Matsum. & Nakai), a member of the family Cucurbitaceae, is one of the most economically important fruit crops cultivated throughout tropical and subtropical regions of the world. Owing to its refreshing taste, high nutritional value andwide consumer acceptance, watermelon has become an indispensable component of horticultural production systems. The fruit contains more than 90% water and serves as an excellent source of vitamins A and C, potassium, magnesium, dietary fibre, citrulline, lycopene, carotenoids andseveral antioxidant compounds that contribute to human health by reducing oxidative stress and lowering the risk of cardiovascular diseases and certain cancers (Kyriacou et al., 2021; Tlili et al., 2022) [17,33] . The increasing awareness of healthy dietary habits, coupled with rising demand for fresh fruits, has significantly enhanced watermelon production worldwide. According to the Food and Agriculture Organization, global watermelon production has continued to increase over the last decade due to improved hybrids, modern cultivation technologies andexpansion of irrigated agriculture (FAOSTAT, 2024) [9] . Watermelon is susceptible to attack by numerous insect pests throughout its growth period, beginning from seedling emergence until fruit harvest. The succulent nature of vines, foliage, flowers andfruits provides favourable feeding and breeding conditions for several phytophagous insects. Both sucking and chewing pests inflict considerable damage either directly through feeding or indirectly by transmitting economically important viral pathogens. These infestations reduce plant vigour, interfere with normal physiological processes, impair flowering and fruit development andultimately decrease marketable yield and fruit quality (Bharathi et al., 2022).

Yield losses attributable to insect pests vary depending on pest species, crop growth stage, climatic conditions, varietal susceptibility andmanagement practices, but severe infestations may result in economic losses exceeding 40-70% under favourable environmental conditions (Patel et al., 2023) [24] . Among the major sucking pests, the cotton aphid, Aphis gossypii Glover, is one of the most destructive species associated with watermelon cultivation. Aphids colonize tender shoots and young leaves, extracting plant sap and causing curling, chlorosis, reduced photosynthetic efficiency andstunted plant growth. Their feeding also results in the excretion of honeydew, which promotes the growth of sooty mould fungi and further interferes with photosynthesis. More importantly, A. gossypii functions as an efficient vector of several economically important viruses, including Cucumber mosaic virus, Watermelon mosaic virus, Papaya ringspot virus-W andZucchini yellow mosaic virus, thereby substantially aggravating crop losses (Nyoike et al., 2021; Zhao et al., 2022) [22, 34] . Similarly, the melon thrips, Thrips palmi Karny, has emerged as a serious pest in cucurbit ecosystems because of its rapid reproductive potential, concealed feeding habit andability to transmit orthotospoviruses. Feeding by thrips causes silvering, leaf distortion, flower abortion andreduced fruit set, significantly affecting both yield and fruit quality (Seal et al., 2022) [29] . Whiteflies (Bemisia tabaci Gennadius) constitute another economically important pest complex in watermelon production. Both nymphs and adults feed on phloem sap, weakening plants and reducing photosynthetic activity. Furthermore, B. tabaci transmits numerous begomoviruses that induce severe viral diseases capable of causing devastating yield reductions. The polyphagous nature, insecticide resistance andremarkable adaptability of B. tabaci have transformed it into one of the most difficult pests to manage in cucurbit production systems (Navas-Castillo et al., 2023) [20] . Other sucking pests such as leafhoppers (Amrasca spp.) and spider mites (Tetranychus urticae Koch) also contribute substantially to productivity losses by causing continuous sap depletion, chlorotic stippling, leaf bronzing, premature senescence andreduced photosynthetic efficiency, particularly under warm and dry environmental conditions (Xu et al., 2021). The economic consequences of these pest infestations extend beyond direct yield reduction. Damage to foliage, flowers andfruits lowers fruit size, sweetness, external appearance andoverall market quality, thereby reducing consumer acceptance and market prices. Farmers often respond by increasing the frequency of insecticide applications, substantially increasing production costs and reducing profit margins. Excessive reliance on synthetic pesticides has also contributed to the development of insecticide resistance, pest resurgence, secondary pest outbreaks, elimination of natural enemies, environmental contamination andpesticide residues in harvested fruits, raising concerns regarding food safety and ecosystem sustainability (Sparks et al., 2023; Bass et al., 2024) [32, 1] . Effective management of insect pests depends largely on understanding their seasonal occurrence and population dynamics under prevailing agroclimatic conditions. Seasonal incidence studies provide valuable information regarding the time of pest appearance, peak population periods, duration of infestation andthe influence of crop phenology on pest abundance. Such information forms the scientific basis for developing integrated pest management (IPM) programmes by enabling farmers to synchronize monitoring, cultural operations, biological control andneed-based insecticide applications with periods of maximum pest vulnerability.

Instead of following calendar-based pesticide schedules, which often result in unnecessary applications, seasonal surveillance facilitates timely interventions based on actual pest incidence, thereby reducing production costs, minimizing pesticide residues andconserving beneficial arthropods (Pedigo & Rice, 2021; Furlong et al., 2022) [25,11] . Consequently, regular pest monitoring has become an indispensable component of sustainable crop protection strategies adopted worldwide. Several studies have demonstrated significant associations between weather parameters and insect pest incidence in cucurbit crops. Positive correlations between maximum temperature and populations of thrips, mites andpumpkin beetles have been reported under tropical production systems, whereas aphid abundance has frequently shown significant relationships with moderate temperatures and relative humidity (Sharma et al., 2022) [30] . Similarly, whitefly populations have been found to increase under warm, dry weather conditions characterized by low rainfall and extended sunshine hours, while prolonged precipitation often suppresses their multiplication (Kumar et al., 2023) [16] . Seasonal fluctuations of Spodoptera litura, Liriomyza spp. andother chewing insects have also been associated with changes in temperature and humidity across different cropping seasons (Biondi et al., 2021) [3] . Although these investigations have contributed significantly to understanding insect ecology, the strength and direction of weather-pest relationships vary considerably among geographical regions because of differences in climate, cropping practices, host cultivars, irrigation methods andlocal biodiversity. Consequently, region-specific studies are indispensable for generating reliable pest forecasting information suitable for local production systems. Tamil Nadu is one of the important horticultural states of India where watermelon cultivation has expanded rapidly due to increasing consumer demand and favourable environmental conditions. The crop is cultivated under diverse agro-ecological situations ranging from irrigated plains to riverbeds and semi-arid regions, exposing it to a wide spectrum of insect pests throughout the growing season. Farmers frequently rely on repeated applications of broad-spectrum insecticides to protect the crop from pest damage, often without considering actual pest population levels or economic threshold limits. Such indiscriminate pesticide use has resulted in increased production costs, accelerated development of insecticide resistance, disruption of natural enemy populations, environmental pollution andconcerns regarding pesticide residues in fruits intended for fresh consumption (Bass et al., 2024) [1] . Furthermore, repeated pesticide exposure may adversely affect pollinators, particularly honey bees, which are essential for successful pollination and fruit set in watermelon. These challenges underscore the need for ecologically sound pest management approaches based on scientific knowledge of pest population dynamics and environmental influences. The integration of meteorological information with pest surveillance has become increasingly important in the era of precision agriculture and climate-smart crop protection. Advances in digital agriculture, remote sensing, automated weather stations andpredictive analytics now enable researchers to develop decision-support systems capable of forecasting pest outbreaks before they reach economically damaging levels (FAO, 2023) [8] . Such forecasting systems reduce unnecessary pesticide applications, lower production costs, improve environmental sustainability andenhance farmers' decisionmaking capacity. However, the success of these systems depends fundamentally on reliable baseline data concerning pest population dynamics and their relationships with local weather conditions. Therefore, generating region-specific ecological information remains a priority for developing effective forecasting models applicable to watermelon production systems in southern India. In view of the economic importance of watermelon, the increasing challenges posed by insect pests andthe limited ecological information available under Tamil Nadu conditions, the present investigation was undertaken to study the seasonal incidence of major insect pests and their association with prevailing weather parameters. The specific objectives were to monitor the population dynamics of major sucking and defoliating insect pests throughout the cropping season, identify the periods of peak infestation, determine the influence of meteorological variables on pest abundance through correlation and regression analyses andgenerate scientific information that could facilitate the development of weather-based pest forecasting models and integrated pest management strategies. The findings of this investigation are expected to contribute to a better understanding of insect pest ecology in watermelon and provide practical recommendations for timely, economically viable andenvironmentally sustainable pest management in the watermelon-growing regions of Tamil Nadu.

Materials and Methods

Experimental Site

The field experiment was conducted during the kharif season of 2021 at a farmer's field located in Akkarampalayam village (11° 08′ 44′′N , 78° 06′ 05′′E) , Namakkal district, Tamil Nadu, India. The study area falls under the tropical agro-climatic zone characterized by warm temperatures and moderate rainfall, making it suitable for watermelon cultivation. The experiment was conducted under open-field conditions to evaluate an integrated pest management (IPM) module against major insect pests of watermelon.

Experimental Crop and Crop Establishment

The popular watermelon hybrid 'Melody' F₁ was used for the investigation. Seeds were sown in protrays and13-day-old healthy seedlings were transplanted to the main field at a spacing of 2.5×0.5m . The crop was maintained by adopting the recommended package of practices for watermelon cultivation prescribed by the Tamil Nadu Agricultural University (TNAU, 2020), except for plant protection measures, which were imposed according to the experimental treatments. Uniform agronomic practices including irrigation, fertilizer application, intercultural operations andweed management were followed throughout the cropping season.

Experimental Design

The experiment was laid out in a Randomized Block Design (RBD) comprising six treatments with adequate replications. The experimental design and analysis followed the standard procedures described by Gomez and Gomez (1984). The treatments were formulated by integrating the best-performing eco-feast crops, botanical pesticides, entomopathogenic fungi andselective insecticide molecules identified from earlier experiments.

Integrated Pest Management (IPM) Components 2.4.1 Ecological Engineering

Ecological engineering was achieved by growing cluster bean (Cyamopsis tetragonoloba) or cowpea (Vigna unguiculata) as intercrops in a 2:1 ratio with watermelon. These flowering intercrops served as nectar and pollen sources for predators, parasitoids andpollinators, thereby improving biological control and enhancing ecosystem services. The ecological engineering approach was adopted according to the habitat management principles recommended by the National Institute of Plant Health Management (NIPHM, 2015).

Botanical Pesticide

Neem oil (3%) was applied as the first component of the IPM module immediately after pest populations approached the economic threshold level. The botanical spray was intended to suppress the initial build-up of sucking pests while minimizing adverse effects on natural enemies and pollinators.

Biological Control

The entomopathogenic fungus Beauveria bassiana (1×10 ⁸cfug⁻¹) was applied as a foliar spray at 8gL⁻¹ following the botanical treatment. The fungal formulation was used to suppress major sucking and foliage-feeding insect pests as part of the biological control component of the IPM module.

Need-based Insecticide Application

Need-based application of selective insecticides was carried out only when pest populations exceeded the economic threshold level. The insecticides evaluated were Chlorantraniliprole 18.5 SC @ 0.6 ml L⁻¹ and Flubendiamide 39.35 SC @ 0.6 ml L ¹. Three rounds of foliar sprays ⁻ were imposed at 15-day intervals. A treated check comprising Thiamethoxam 25 WG @ 0.4 g L⁻¹ and an untreated control receiving water spray alone were maintained for comparison.

Field Sanitation

Regular field sanitation was maintained throughout the cropping period by removing weeds, alternate host plants, infested leaves, damaged vines andcrop residues. Balanced fertilizer application and proper irrigation scheduling were followed to maintain healthy crop growth and reduce pest incidence.

Pest Monitoring and Data Collection

Ten plants were selected randomly from each replication and tagged for recording observations throughout the crop growth period. Pest observations were recorded before treatment application and subsequently at 1, 3, 7 and14 days after each spray. Weekly observations were continued until harvest. Standard sampling methods described by Naik et al. (2019) and Udhayakumar (2020) were followed for recording insect populations.

Pest Population

The population of aphids (Aphis gossypii), thrips (Thrips palmi), whiteflies (Bemisia tabaci), leafhoppers andred spider mites (Tetranychus urticae) was recorded from the top three leaves (one unopened terminal leaf and two fully expanded leaves) of each observation plant. The incidence of leaf miners, red pumpkin beetles (Aulacophora foveicollis), leaf-eating caterpillars (Spodoptera litura) andfruit flies was assessed on a whole-plant basis at weekly intervals using standard field sampling procedures.

Natural Enemies and Pollinators

The abundance of natural enemies including coccinellid beetles, green lacewings (Chrysoperla spp.), spiders, predatory bugs andparasitoids was recorded simultaneously from the tagged plants. Pollinator activity, particularly honey bees and other flower-visiting insects, was also recorded during the flowering period to assess the ecological compatibility of the IPM module.

Fruit Yield

Marketable fruits from each treatment were harvested at physiological maturity, weighed individually andconverted into tonnes per hectare (tha⁻¹) for comparison among treatments.

Residue Analysis

Fruit samples collected from the most effective treatments were stored at-20 °C until analysis. Pesticide residues were determined using the QuEChERS extraction method followed by High-Performance Liquid Chromatography (HPLC) according to the procedure described by Anastassiades et al. (2003).

Economic Analysis

Gross return, net return andthe Incremental Cost-Benefit Ratio (ICBR) were calculated using the prevailing market price of watermelon fruits. The ICBR was determined following the procedure described by Akila and Sundara Babu (1994) by considering the total cost of cultivation and plant protection expenses.

Statistical Analysis

The experimental data on pest incidence, natural enemy abundance, fruit yield andeconomic returns were subjected to analysis of variance (ANOVA) appropriate for a Randomized Block Design following Gomez and Gomez (1984). Count data were transformed using surd (X+0.5) before analysis to stabilize variance. Treatment means were separated using Tukey's Honest Significant Difference (HSD) test at P≤0.05 (Tukey, 1949) [35] . Statistical analyses were performed using IBM SPSS Statistics version 22.

Results

Effect of Integrated Pest Management Module on Major Insect Pest Suppression

The integrated pest management (IPM) modules significantly influenced the suppression of major insect pests infesting watermelon under field conditions. Among the evaluated treatments, the cluster bean-based IPM module [T₁: Cluster bean (2:1) + Neem oil (3%) + Beauveria bassiana (1×10 ⁸ cfu g⁻¹ @ 8gL⁻¹) + Chlorantraniliprole 18.5 SC @ 0.6 ml L ¹] ⁻ consistently recorded the highest suppression of all major sucking and chewing insect pests throughout the cropping season. The aphid (Aphis gossypii) population was reduced by 65.61% in T₁ . , followed by T₃ (60.57%), T₂ (54.97%), T₄ (47.42%), while the farmer's practice (T₅) recorded the lowest suppression (39.78%). Likewise, the highest reduction in thrips (Thrips palmi) population was recorded in T₁ (84.00%), followed by T₃ (80.85%), T₂ (76.95%), T₄ (70.22%) and Γ ₅ (68.00%). A similar trend was observed for whitefly (Bemisia tabaci), wherein T₁ recorded the highest suppression (78.38%), followed by T₃ (73.96%), T₂ (70.22%), T₄ (64.72%), whereas the lowest suppression was recorded under farmer's practice (56.92%). Leafhopper (Amrasca biguttula biguttula) incidence was reduced by 73.90% in T₁ , followed by 69.71% in T₃ , 64.24% in T₂ . , 59.51% in T₄ and 57.35% in T₅ . The IPM modules were equally effective against chewing pests. The maximum reduction in red spider mite (Tetranychus urticae) was observed in T₁ (71.29%), followed by T₂ (66.02%), T₃ (60.67%), T₄ (57.35%) and Γ ₅ (55.64%). Leaf miner infestation was reduced by 73.80% in T 1: , followed by 68.00% in T₃ and 62.71% in T₂ . . Likewise, the highest reduction in leaf-eating caterpillar (Diaphania indica) was recorded in T₁ (76.14%), followed by T₃ (70.04 %) T₂ (67.18%), T₄ (63.61%) and T₅ (61.97%). Melon fruit fly (Bactrocera cucurbitae) infestation was also effectively suppressed, with the highest reduction recorded in T₁ (80.04%), followed by T₃ (79.82%), T₂ (79.02%), T₄ (72.72%), while the lowest reduction was observed in T₅ (68.01%). Overall, the cluster bean-based IPM module demonstrated superior efficacy by maintaining pest populations below the economic threshold level throughout the crop growth period.

Conservation of Natural Enemies and Pollinators

The integrated pest management modules significantly enhanced the conservation of beneficial arthropods compared with the insecticide-based farmer's practice. Among the treated plots, T₁ supported the highest abundance of coccinellid beetles (2.12 adults plant ¹), followed by⁻ T₃ (

Effect of Integrated Pest Management Modules on Fruit Yield

The integrated pest management (IPM) modules significantly influenced marketable fruit yield of watermelon (Table 4). Among the different treatments, the cowpea-based IPM module [T₃: Cowpea (2:1) + Neem oil (3%) + Beauveria bassiana + Chlorantraniliprole 18.5 SC @ 0.6 ml L⁻¹] recorded the highest fruit yield of 27.50tha⁻¹ , which was closely followed by the cluster bean-based IPM module (T₁) with 26.50tha⁻¹ . The cluster bean module integrated with flubendiamide (T₂) produced 25.50tha⁻¹ , whereas the cowpea module integrated with flubendiamide (T₄) recorded 23.30tha⁻¹ . The conventional farmer's practice (T₅) resulted in the lowest marketable fruit yield of 20.30tha⁻¹ among all protected treatments. The higher fruit yield observed in T₃ and T₁ could be attributed to effective suppression of sucking and chewing insect pests during the critical vegetative, flowering andfruit development stages, resulting in improved photosynthetic activity, better fruit set andreduced fruit damage. Moreover, ecological engineering through flowering intercrops promoted the abundance of pollinators and natural enemies, which contributed to enhanced pollination efficiency and sustainable pest regulation. In contrast, repeated reliance on insecticides under the farmer's practice adversely affected beneficial arthropods and provided comparatively lower seasonlong pest suppression, ultimately resulting in reduced fruit yield. The untreated control recorded the lowest yield owing to severe pest infestation and extensive crop damage throughout the growing period.

Economic Analysis

The economic analysis clearly demonstrated the superiority of the integrated pest management modules over the conventional farmer's practice (Table 5). Among the evaluated treatments, the cluster bean-based IPM module (T₁) recorded the highest Incremental Cost-Benefit Ratio (ICBR) of 1:4.83, indicating the greatest economic return per unit investment. This was closely followed by the cowpea-based IPM module (T₃) with an ICBR of 1:4.71, whereas T₂ and T₄ recorded ICBRs of 1:4.39 and 1:4.14, respectively. The lowest economic return among the treated plots was obtained under the farmer's practice (T₅) , which recorded an ICBR of 1:3.57. Although the establishment of flowering intercrops and application of biological control agents slightly increased the initial cultivation cost, the investment was compensated by substantial reductions in pest incidence, lower crop losses, higher marketable yield andreduced dependence on repeated insecticide applications. The combination of ecological engineering, botanical pesticides, entomopathogenic fungi andneed-based insecticides proved to be economically viable by improving productivity while minimizing unnecessary pesticide expenditure. Consequently, the integrated modules generated greater net returns than the insecticide-based conventional practice, confirming their suitability for commercial watermelon production.

Validation of the Integrated Pest Management Module

The field validation experiment confirmed the effectiveness of the developed integrated pest management module under farmers' field conditions. Among all treatments, the cluster beanbased IPM module (T₁) emerged as the most balanced and sustainable pest management strategy. The module reduced aphid, thrips, whitefly, leafhopper, mite, leaf miner, leaf-eating caterpillar andmelon fruit fly populations by 65.61-84.00%, while simultaneously conserving higher populations of coccinellids, lacewings, syrphid flies, spiders andbee pollinators compared with the farmer's practice. Furthermore, the module produced a marketable fruit yield of 26.50tha⁻¹ and generated the highest Incremental Cost-Benefit Ratio (1:4.83) among all evaluated treatments. Although the cowpea-based IPM module (T₃) produced the highest fruit yield (27.50tha⁻¹) its economic return (ICBR 1:4.71) was marginally lower than that of T₁ . Therefore, considering pest suppression efficiency, conservation of beneficial arthropods, economic profitability, environmental safety andease of adoption by farmers, T₁ was identified as the most suitable integrated pest management module for sustainable watermelon cultivation. The validation study further demonstrated that integration of ecological engineering, neem oil, Beauveria bassiana andneed-based application of chlorantraniliprole effectively maintained pest populations below the economic threshold level, reduced reliance on synthetic insecticides, improved biodiversity andenhanced crop productivity. Hence, the validated IPM module can be recommended for large-scale adoption in watermelon-growing regions of Tamil Nadu and similar agro-ecological conditions.

Discussion

The present investigation clearly demonstrated that integrating ecological engineering, botanical pesticides, entomopathogenic fungi andselective insecticides provided significantly better suppression of major insect pests than the conventional insecticide-based management practice. The superior performance of the cluster bean-and cowpea-based IPM modules highlights the importance of combining multiple compatible pest management tactics that act through different ecological and biological mechanisms. Rather than relying solely on chemical insecticides, the integration of flowering intercrops, neem oil, Beauveria bassiana andneedbased application of chlorantraniliprole effectively disrupted pest colonization, reduced population build-up, enhanced natural biological control andmaintained pest populations below the economic threshold level throughout the crop season. Neem oil served as an effective botanical component of the IPM module by suppressing early infestations of sucking pests without adversely affecting beneficial arthropods. The bioactive compound azadirachtin interferes with insect feeding, moulting, oviposition andreproduction, thereby reducing pest populations through multiple physiological pathways. Unlike broadspectrum synthetic insecticides, neem-based products exhibit comparatively lower toxicity toward predators, parasitoids andpollinators, making them highly compatible with biological control programmes. The successful integration of neem oil with ecological engineering observed in the present study corroborates the findings of Isman (2020) [14] and Benelli et al.

(2023) [2] , who reported that botanical pesticides represent valuable components of sustainable integrated pest management because of their selective toxicity, biodegradability andreduced environmental persistence. The entomopathogenic fungus Beauveria bassiana further enhanced the effectiveness of the IPM module by providing biological suppression of both sucking and foliage-feeding insect pests. Once the fungal spores contacted susceptible insects, they germinated on the insect cuticle, penetrated the integument, proliferated within the haemocoel andeventually caused insect mortality. Besides direct pathogenicity, fungal infection reduces feeding activity and reproductive capacity before insect death, thereby contributing to long-term population suppression. The compatibility of B. bassiana with neem oil and ecological engineering allowed the conservation of beneficial insects while reducing dependence on repeated chemical insecticide applications. Similar synergistic interactions between entomopathogenic fungi and botanical pesticides have been reported by Mascarin and Jaronski (2022) [18] and Ruiu (2023) [28] , who concluded that microbial biopesticides provide environmentally safe alternatives for managing insect pests within integrated pest management programmes. The final component of the IPM module involved the needbased application of chlorantraniliprole only after pest populations exceeded the economic threshold level. Unlike calendar-based insecticide applications commonly adopted by farmers, threshold-based intervention minimized unnecessary pesticide use while maintaining effective pest suppression. Chlorantraniliprole, belonging to the anthranilic diamide group, possesses a unique mode of action by activating insect ryanodine receptors, leading to muscle paralysis and rapid cessation of feeding. Its high selectivity toward target pests and relatively lower toxicity to beneficial arthropods make it particularly suitable for integration into IPM programmes. The superior performance of chlorantraniliprole-based modules observed in the present study agrees with reports by Sparks et al. (2023) [32] and Cordova et al. (2021) [5] , who demonstrated that selective insecticides can effectively complement biological control and ecological engineering while minimizing disruption of natural enemy populations. An important outcome of the present investigation was the conservation of pollinator diversity under the integrated modules. Watermelon is highly dependent on insect-mediated crosspollination for optimum fruit set, fruit size andseed development. The higher abundance of Apis dorsata, Apis cerana indica andApis florea recorded in the IPM plots indicates that the integrated approach created a pollinatorfriendly environment by reducing exposure to broadspectrum insecticides and increasing the availability of floral resources. Similar improvements in pollinator abundance following habitat diversification have been documented by Blaauw and Isaacs (2021) [4] and Nicholson et al. (2022) [21] , who demonstrated that flowering strips surrounding crop fields substantially improve pollination services while simultaneously supporting natural enemy communities. One of the major strengths of the developed integrated pest management module is its contribution to sustainable watermelon production. Conventional watermelon cultivation in many parts of India largely depends on repeated applications of broad-spectrum insecticides, often applied prophylactically without monitoring pest populations or considering economic threshold levels. Such indiscriminate pesticide use has resulted in insecticide resistance, resurgence of secondary pests, contamination of soil and water resources, pesticide residues in fruits andadverse impacts on biodiversity and human health. In contrast, the present investigation demonstrated that integrating ecological engineering, biological control, botanicals andselective insecticides substantially reduced reliance on chemical pesticides while maintaining effective pest suppression. The sequential application strategy adopted in the present study ensured that chemical insecticides were used only when absolutely necessary. Early-season pest suppression was primarily achieved through habitat manipulation, neem oil andBeauveria bassiana, thereby avoiding multiple insecticide sprays during the initial stages of crop growth. Consequently, the total pesticide load imposed on the cropping system was considerably lower than that under the conventional farmer's practice. Similar reductions in insecticide usage have been reported by Pretty and Bharucha (2021) [26] , Desneux et al. (2022) [6] andFAO (2023), who emphasized that integrated pest management can reduce pesticide use by 30-70% without compromising crop productivity. The success of any integrated pest management (IPM) programme depends not only on its biological effectiveness but also on its technical feasibility, economic viability andease of adoption by farmers. The present investigation demonstrated that the developed IPM modules satisfy all these requirements by integrating readily available cultural, biological, botanical andchemical control measures into a practical management strategy. The cluster bean-based IPM module effectively reduced the populations of major sucking and chewing insect pests, conserved beneficial arthropods, increased marketable fruit yield andgenerated the highest economic return. These advantages make the validated IPM module highly suitable for adoption by watermelon growers under Tamil Nadu conditions. Economic profitability remains the primary factor influencing farmers' decisions regarding pest management technologies. Although the integrated modules involved slightly higher initial investment for establishing flowering intercrops and biological control agents, the additional expenditure was compensated by lower crop losses, higher marketable fruit yield, improved fruit quality andreduced pesticide consumption. The highest Incremental Cost-Benefit Ratio (ICBR) recorded by the cluster bean-based IPM module clearly indicates that integrated pest management is economically more profitable than repeated insecticide applications. Similar economic advantages of integrated pest management have been reported in cucurbit crops by Pretty and Bharucha (2021) [26] , FAO (2023) andParolin et al. (2021) [23] , who concluded that ecological approaches increase farm profitability by reducing pesticide expenditure while maintaining or improving crop productivity.

Another important factor supporting farmer adoption is the reduced risk of insecticide resistance. Repeated application of insecticides having similar modes of action has resulted in widespread resistance among aphids, whiteflies, thrips andother economically important vegetable pests. The integrated approach developed in the present study combines multiple control tactics with different mechanisms of action, thereby reducing selection pressure on pest populations and delaying the development of resistance. Furthermore, the use of thresholdbased insecticide application minimizes unnecessary pesticide exposure, which is one of the principal drivers of resistance evolution (Bass et al., 2024; Sparks et al., 2023) [1,32] . The conservation of pollinators and natural enemies observed in the present study further enhances the practical value of the validated IPM module. Flower-visiting bees are essential for optimum fruit set and fruit quality in watermelon, whereas predators and parasitoids provide continuous natural suppression of insect pests. Conservation of these beneficial organisms reduces future pest outbreaks and strengthens ecosystem resilience, thereby providing longterm benefits beyond a single cropping season. Such ecological services reduce production risks and improve system stability, making the IPM module particularly attractive for resourcepoor farmers who cannot afford repeated pesticide applications. The widespread adoption of the developed IPM strategy can be further strengthened through farmer training programmes, front-line demonstrations, farmer field schools andextension campaigns emphasizing pest monitoring and economic threshold-based decision making. Digital advisory services, mobile applications andweather-based pest forecasting systems can also facilitate timely implementation of IPM components. Collaboration among research institutions, extension agencies, input suppliers andfarmer producer organizations will be essential for scaling up adoption across major watermelongrowing regions.

Conclusion

the present investigation demonstrated that integrating ecological engineering, botanical pesticides, microbial biocontrol agents andselective need-based insecticides provides a robust and sustainable strategy for watermelon pest management. The validated IPM module effectively suppressed major insect pests, conserved natural enemies and pollinators, reduced dependence on synthetic pesticides, increased fruit yield andgenerated superior economic returns compared with the conventional farmer's practice. The findings strongly support the adoption of ecological intensification approaches for sustainable watermelon production and contribute to national efforts aimed at promoting environmentally responsible crop protection, improving farmer profitability andensuring safe, residue-minimized food production.

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