Field evolution of management practices against bitter gourd fruit fly (Zeugodacus cucurbitae)

Introduction

Bitter gourd (Momordica charantia L.) is an economically important cucurbitaceous vegetable belonging to the family Cucurbitaceae. It is widely cultivated in tropical and subtropical regions worldwide and is highly valued for its nutritional, medicinal, and commercial importance. The crop is believed to have originated in tropical Asia and is extensively grown in India, China, Bangladesh, Sri Lanka, Thailand, Malaysia, Indonesia, and several African countries. India is one of the leading producers and consumers of bitter gourd, which is cultivated across diverse agroclimatic conditions due to its adaptability, high market demand, and profitability. In India, vegetable cultivation plays a vital role in ensuring nutritional security, generating employment, and enhancing farmers' income. Among vegetable crops, cucurbits occupy an important position owing to their short duration, high productivity, and consumer preference. According to the National Horticulture Board (2023-24), bitter gourd is cultivated over approximately 105 thousand hectares, producing about 1.30 million tonnes annually, with an average productivity of 12.4 t ha⁻¹. The crop is extensively cultivated in Uttar Pradesh, Bihar, West Bengal, Odisha, Maharashtra, Karnataka, Tamil Nadu, Andhra Pradesh, and several northeastern states. Bitter gourd is recognised as a functional food because of its high nutritional value and the presence of biologically active compounds such as charantin, momordicin, vicine, and polypeptide-P, which exhibit antidiabetic, antioxidant, antimicrobial, and anti-inflammatory properties. These health-promoting attributes, together with increasing consumer awareness, have contributed to the expansion of bitter gourd cultivation in recent years.

Despite its economic importance, bitter gourd production is severely constrained by several insect pests, among which the melon fruit fly, Bactrocera cucurbitae (Coquillett) (Diptera: Tephritidae), is considered the most destructive. Female flies puncture tender fruits for oviposition, and the developing maggots feed internally on the fruit pulp, causing fruit deformation, premature fruit drop, rotting, and complete loss of marketability. Depending on the severity of infestation and prevailing environmental conditions, yield losses may range from 30 to 100%, making the pest a major constraint to profitable bitter gourd cultivation. Management of B. cucurbitae has largely depended on repeated applications of synthetic insecticides. These concerns have highlighted the need for sustainable, environmentally safe management strategies grounded in integrated pest management (IPM) principles. A thorough understanding of the seasonal incidence and population dynamics of B. cucurbitae under local agro-climatic conditions is essential for developing effective and timely management strategies. Therefore, the present investigation was undertaken to evaluate the incidence of melon fruit fly on bitter gourd and to generate information to support the development of sustainable management practices to minimise crop losses and improve productivity.

Materials and Methods

Experimental site

The experiment was conducted during the Zaid season (February-June 2025) at the Students' Instructional Farm, Faculty of Agriculture, Kamla Nehru Institute of Physical and Social Sciences (Autonomous), Sultanpur, Uttar Pradesh, India. Laboratory observations were carried out in the Entomology Laboratory of the Department of Entomology. The experimental site is located at 26.26°N and 82.07°E, at an altitude of approximately 95 m above mean sea level. The region experiences a subtropical climate with hot summers, moderate monsoon rainfall, and cool winters. The experimental field had sandy loam soil with good drainage. Daily weather data, including maximum and minimum temperature, relative humidity, and rainfall, were obtained from the institute's meteorological observatory for correlation with fruit fly incidence.

Crop establishment

The bitter gourd variety 'Pusa Do Mausami' was sown on 25 February 2025. Seeds were sown on raised beds at a spacing of 1.5 × 1.5 m, with one healthy plant maintained per hill after thinning. The recommended agronomic practices package, including irrigation, weeding, and intercultural operations, was uniformly followed throughout the crop growth period.

Nutrient management

Well-decomposed farmyard manure (FYM) at 20 t ha⁻¹ was incorporated during land preparation. Chemical fertilizers were applied at the recommended dose of 100:50:50 kg N: P₂O₅:K₂O ha⁻¹. The entire quantity of phosphorus and potassium, along with half of the nitrogen, was applied as a basal dose, while the remaining nitrogen was top-dressed in two equal splits during crop growth.

Irrigation

The crop was irrigated immediately after sowing to ensure proper germination. Subsequent irrigations were provided at 7-10-day intervals depending on soil moisture status and prevailing weather conditions.

Experimental observations

Fruit fly incidence was monitored at regular intervals from the first appearance of the pest until the final harvest. Observations on fruit infestation and other experimental parameters were recorded according to the treatment schedule. Weather parameters recorded during the crop season were used to study their relationship with the population dynamics of the melon fruit fly (Bactrocera cucurbitae Coquillett). 1; Fig. 1). Thereafter, the pest population gradually declined towards crop maturity. The increase in fruit fly incidence during the fruiting stage may be attributed to the greater availability of suitable fruits for oviposition, coupled with favourable environmental conditions that promoted pest development and survival. [2] and Sunil et al. (2017) [5] , who observed increased abundance of spiders during periods of high fruit fly infestation. [1] and Verghese and Ramani (2011) [6] . Among all treatments, Chlorantraniliprole 18.5 SC @ 0.3 ml L⁻¹ proved most effective by reducing larval population to 0.76 larvae fruit⁻¹ at 7 DAS, followed closely by Spinosad 45 SC (0.92 larvae fruit⁻¹). Flubendiamide also provided satisfactory control, whereas Neem oil showed moderate effectiveness. Imidacloprid was comparatively less effective. The untreated control maintained consistently high larval populations throughout the observation period. The superior performance of chlorantraniliprole may be attributed to its excellent translaminar activity and prolonged residual effect, whereas spinosad acts rapidly by affecting the insect nervous system, resulting in quick mortality. The lowest infestation (8.76% at 7 DAS) was recorded with chlorantraniliprole, followed by spinosad (10.42%). Neem oil and emamectin benzoate showed moderate suppression, while imidacloprid was comparatively less effective. The untreated control recorded continuously increasing infestation, reaching 54.86% by 14 DAS. The marked reduction in infestation under chlorantraniliprole and spinosad treatments demonstrates their ability to effectively suppress larval establishment and minimize economic losses. The highest fruit yield (5.45 kg plot⁻¹) was recorded with Chlorantraniliprole 18.5 SC, representing an 81.66% increase over control. This was closely followed by Spinosad 45 SC, which produced 5.18 kg plot⁻¹ and increased yield by 72.66%. Emamectin benzoate also produced satisfactory yields, whereas Neem oil and Flubendiamide recorded comparatively lower productivity. The untreated control produced the lowest yield (3.00 kg plot⁻¹) due to severe fruit fly infestation. The improvement in yield under chlorantraniliprole and spinosad treatments may be attributed to their effective suppression of larval damage, resulting in higher retention of marketable fruits. Overall, the present investigation clearly demonstrates that chlorantraniliprole 18.5 SC followed by spinosad 45 SC offers the most effective management of Z. cucurbitae under eastern Uttar Pradesh conditions and can be incorporated into integrated pest management programmes to achieve sustainable bitter gourd production.

Conclusion

The melon fruit fly (Zeugodacus cucurbitae) remains one of the most destructive insect pests affecting bitter gourd crops under the agro-climatic conditions of eastern Uttar Pradesh during the Zaid season. Pest populations remain active throughout the cropping period, steadily increasing as plants transition from vegetative growth to the fruiting stage. Activity reaches its absolute peak during the 23rd Standard Meteorological Week, which sees the highest adult trap catches, larval densities, and fruit damage confirming that the fruiting stage is the most vulnerable phase requiring immediate control measures. Seasonal abundance is heavily driven by local weather dynamics. In particular, higher minimum temperatures and elevated relative humidity create optimal conditions for rapid pest multiplication. Because microclimate plays such a critical role in population spikes, weather-based forecasting serves as an effective early warning system to schedule protective measures before economic crop loss occurs.

Biological studies reveal that the pest possesses a high reproductive capacity, characterized by a rapid development cycle of 17-18 days and an average fecundity of roughly 119 eggs per female. This combination allows Z. cucurbitae to complete multiple overlapping generations within a single season, explaining the sudden field surges and severe fruit rot observed under favorable weather. Natural enemy observations highlight spiders as the primary predatory arthropods in the bitter gourd ecosystem. Their numbers naturally track fruit fly density, signaling their key role in biological pest suppression. Field evaluations demonstrate that chemical control using chlorantraniliprole 18.5 SC @ 0.3 ml/L or spinosad 45 SC @ 0.3 ml/L provides superior protection by drastically reducing larval damage and increasing marketable yields. For sustainable long-term protection, these selective insecticides should be paired with field sanitation, cuelure trapping, cultural practices, and spider conservation within a location-specific Integrated Pest Management (IPM) framework.

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