Integrated management of fruit borer complex in brinjal using IPM module

Introduction

Brinjal growers in Nueva Ecija face a stubborn problem: the shoot and fruit borer (Leucinodes orbonalis) tunnels into developing fruits, rendering them unmarketable, and no single control tactic has proved sufficient on its own [1] . Farmers in the Muñoz region typically spray synthetic pyrethroids 8-12 times per cropping season, a practice that raises production costs, leaves chemical residues on harvested fruit, and kills natural enemies such as parasitoid wasps and predatory bugs [2] . Brinjal (Solanum melongena L.) is one of the most consumed vegetables in the Philippines, with significant production across Luzon and Visayas [3] . L. orbonalis is its most destructive pest across South and Southeast Asia; larvae bore into shoots during the vegetative phase and into fruits from flowering onward, causing yield losses of 30-70% under unprotected conditions [4] . Resistance to cypermethrin and other pyrethroids has been documented in multiple Philippine provinces [5] . Integrated pest management (IPM) combines cultural, biological, mechanical, and judicious chemical methods so that no single tactic carries the full burden of control [6] . Pheromone traps for adult moth monitoring and mass trapping, egg parasitoids such as Trichogramma chilonis, botanical sprays based on neem (Azadirachta indica), and microbial agents like Bacillus thuringiensis have each shown partial efficacy against L. orbonalis in isolation [7,8] . But field-validated multi-component IPM modules -tested as complete packages rather than as isolated tactics -are few, particularly for the Central Luzon region of the Philippines [9] . The present research was designed to assemble and field-test a six-component IPM module against L. orbonalis in brinjal, comparing its performance with chemical-only, bio-agentonly, and trap-crop-only strategies under rainfed wet season conditions at Muñoz.

Field Experimental Design

The experiment was arranged in a randomised block design with five treatments and three replications, giving 15 plots of 5 m × 4 m each. Treatments were: T 1 -untreated control; T 2chemical spray (cypermethrin 25 EC at 0.5 mL L⁻¹, fortnightly from 30 DAT); T

Seasonal Pest Dynamics

Borer activity followed a bimodal pattern in both years. The first peak occurred in August-September when temperatures averaged 28-31 °C and relative humidity exceeded 85%, conditions that favour L. orbonalis oviposition [10] . A second, smaller peak appeared in late October as fruit load increased. Pheromone trap catches confirmed these peaks, with moth counts averaging 14.

Results

All four management treatments reduced fruit infestation compared with the untreated control, but the magnitude of reduction varied widely. The IPM module brought mean fruit infestation down to 11.2%, followed by chemical spray (18.1%), trap crop (23.1%), and bio-agent alone (25.8%), against 34.9% in the control. Shoot infestation followed a similar ranking.

Comprehensive Interpretation

The IPM module's superiority arose from the additive and complementary action of its six components. Pheromone traps intercepted male moths and reduced mating success; neem oil deterred oviposition on treated surfaces; Trichogramma parasitised eggs before larvae could enter fruit; Bt spray killed early-instar larvae on foliage; infestedshoot clipping removed hidden larvae mechanically; and castor border rows diverted gravid females away from the main crop. No single component in isolation delivered the 67.9% reduction that the module achieved as a package.

Discussion

The 67.9% reduction in fruit infestation under the IPM module is comparable to the 60-72% range reported by Alam et al. from a similar multi-tactic trial in Bangladesh [11] . The mechanism behind this consistency is the disruption of the pest's life cycle at multiple stages -egg, early larva, late larva, and adult -so that survivors of one tactic face another. For the Muñoz grower, this means fewer damaged fruits reaching the market and, critically, no detectable insecticide residue on produce.

Chemical spray alone reduced infestation by 48.1%, yet GC-ECD analysis detected cypermethrin residues of 0.14-0.21 mg kg⁻¹ on fruit sampled two days before harvestexceeding the Codex MRL of 0.05 mg kg⁻¹ for brinjal [12] . This finding underlines the food-safety risk of calendarbased pyrethroid sprays and strengthens the case for nonchemical alternatives. The bio-agent-only treatment (Bt kurstaki) was the weakest single-tactic option (26.1% reduction), consistent with earlier observations that Bt works best when larvae are exposed on the plant surface rather than already inside the fruit [13] . The benefit-cost ratio of the IPM module (3.6) exceeded that of chemical spray (2.8) largely because the module's input costs (pheromone lures, Trichogramma cards, neem oil) are lower per season than 8-10 rounds of cypermethrin, and the healthy-fruit yield premium (26.7 vs. 21.8 t ha⁻¹) widened the revenue gap [14] . Extension adoption, however, hinges on the availability of Trichogramma cards and reliable pheromone lure supply chains in rural Nueva Ecija -a logistics bottleneck that current government bio-control programmes have only partially addressed [15] .

Conclusion

This research demonstrates that a six-component IPM module can cut brinjal fruit borer infestation to 11.2% and lift healthy fruit yield to 26.7 t ha⁻¹ -outperforming chemical-only management by a wide margin while eliminating pesticide residues on harvested fruit. The supporting data from two consecutive wet seasons at Muñoz confirm the module's robustness across years with different rainfall patterns. The significance lies in offering Central Luzon growers a practical, economically viable, and food-safe alternative to pyrethroid-dependent pest control. Open questions include the module's performance under irrigated dry-season brinjal, the feasibility of scaling Trichogramma production at the district level, and whether pheromone-based mating disruption could replace mass trapping for even better adult suppression [16,17] .

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