Bio-efficacy of different insecticides against girdle beetle (Obereopsis brevis Swedenbord) in soybean crop
Abstract
Soybean (Glycine max L. Merrill) is an economically important oilseed and protein-rich legume crop; however, its productivity is substantially constrained by insect pests, among which the girdle beetle, Obereopsis brevis, is one of the most destructive pests in soybean-growing regions of India. The present investigation was conducted during the Kharif seasons of 2024 and 2025 at the Research Farm, School of Agriculture Science, Bhopal, Madhya Pradesh, to evaluate the bio-efficacy and economic potential of different insecticides against soybean girdle beetle. Seven treatments comprising thiamethoxam 25% WG, imidacloprid 17.8% SL, fipronil 5% SC, lambda-cyhalothrin 5% EC, cartap hydrochloride 50% SP, chlorantraniliprole 18.5% SC, and an untreated control were evaluated under field conditions. The efficacy of the treatments was assessed based on girdle beetle infestation before spraying and at 1, 3, 7, and 10 days after each spray. Grain yield and incremental cost-benefit ratio (ICBR) were also determined to assess the economic feasibility of the treatments.The results revealed significant differences among the insecticides in suppressing O. brevis infestation during both years. Chlorantraniliprole 18.5% SC consistently exhibited the highest efficacy, recording the lowest pest population throughout the observation period. During 2024, chlorantraniliprole reduced the pest population by 61.47% at 7 days after the first spray and by 86.68% and 86.94% at 7 and 10 days after the second spray, respectively, over the untreated control. Fipronil 5% SC was the next most effective treatment, followed by cartap hydrochloride 50% SP. A similar trend was observed during 2025, with chlorantraniliprole recording the lowest pest population at 7 days after the first spray and maintaining superior suppression after the second spray. The untreated control consistently recorded the highest pest population and progressive pest resurgence. The superior performance of chlorantraniliprole was attributed to its rapid action and prolonged residual activity against the girdle beetle. Overall, chlorantraniliprole 18.5% SC emerged as the most promising treatment for effective management of O. brevis in soybean, followed by fipronil 5% SC and cartap hydrochloride 50% SP. The findings indicate that timely application of effective insecticides can substantially reduce girdle beetle infestation and contribute to improved soybean productivity and economic returns.
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Introduction
Soybean (Glycine max L. Merrill), belonging to the family Fabaceae, is one of the world's most important grain legumes and a major source of edible oil and high-quality plant protein. Often referred to as the "golden bean" or "miracle crop," it plays a vital role in global food, nutritional, and economic security. In India, soybean has become a leading oilseed crop due to its high nutritional value, adaptability, and profitability. During the 2024-2025 crop year, soybean was cultivated on approximately 126.90 lakh hectares, reflecting increasing farmer preference supported by improved varieties, favorable market prices, and government initiatives promoting oilseed production. Madhya Pradesh, known as the "Soybean Bowl of India," contributed the largest share with 53.48 lakh hectares, followed by Maharashtra (51.36 lakh hectares) and Rajasthan (11.25 lakh hectares) (Anonymous 2025) [1] . Despite its economic importance, soybean production is severely constrained by numerous insect pests. Around 130 insect pest species have been reported on soybean in Madhya Pradesh alone (Singh and Verma, 1988) [8] among the major pests are stem fly (Melanagromyza sojae), girdle beetle (Obereopsis brevis), green semilooper (Chrysodeixis acuta), tobacco caterpillar (Spodoptera litura), Bihar hairy caterpillar (Spilosoma obliqua), whitefly (Bemisia tabaci), jassid (Apheliona maculosa), and blue beetle (Cneorane spp.). These pests collectively cause significant quantitative and qualitative yield losses, with their incidence varying across different agro-climatic regions. Among them, the girdle beetle (Obereopsis brevis) has emerged as one of the most destructive pests of soybean. First reported in Madhya Pradesh in 1969 with about 13.5% plant infestation, its severity has increased considerably over the years, causing up to 80% plant damage in highly affected areas. Other pests also contribute substantially to crop losses; the green semilooper damages nearly 35% of flowers and 24% of pods, while the stem fly may cause up to 40% yield loss during winter and over 90% plant infestation under rainy-season conditions. Similarly, Spodoptera litura causes extensive defoliation during the kharif season, particularly from mid-August to October (Singh and Singh, 1987) [7] & (Ramesh Babu, 2010) [9] . The damaging stage of the girdle beetle is the larva, which bores into the stem and branches, disrupting the plant's vascular system and restricting the movement of water and nutrients. This internal feeding results in stunted growth, wilting, branch drying, lodging, and even complete plant death under severe infestation. Adult females girdle the petioles and sometimes the main stem by making characteristic ring-like cuts, which weaken the plant and facilitate larval entry. The pest is particularly destructive during the 30-55 days after sowing, when soybean plants are in their active vegetative growth stage. Infestation during this critical period has a direct and significant impact on crop growth and final yield.
Owing to its increasing incidence, destructive feeding habit, and potential to cause severe economic losses, the girdle beetle has become a major biotic constraint in soybean cultivation. Therefore, the development and adoption of effective, timely, and sustainable management strategies are essential to minimize crop losses and ensure stable soybean productivity.
Materials and Methods
Estimation of Bio-efficacy of insecticides against Soybean girdle beetle
The percent damage of stem girdler was estimated by counting the number of girdled plants damaged by the beetle and total number of plants in a meter row length. Three such meter row length spots were randomly selected per plot was recorded 24 hours before spray and after 1,3,7 and 10 days of each spray.
Percent damage (%) = Number of infescted plant Total number of plant × 100
Grain Yield and Economic Evaluation of Insecticide Treatments
Grain yield was recorded by harvesting each experimental plot separately, followed by weighing the grains obtained from each plot and expressing the yield in kilograms per plot. The grain yield was subsequently converted into quintals per hectare (q ha⁻¹) based on the respective plot area. To assess the economic feasibility of the tested insecticides for the management of stem girdler in soybean, the Incremental Cost-Benefit Ratio (ICBR) was calculated.
The economic returns obtained from each insecticide treatment were compared with those of the untreated control. The cost of treatment included the expenditure incurred on insecticides and labour charges, while the economic returns were determined based on the additional yield and corresponding returns obtained over the control.
The ICBR was used to identify the most economically viable and feasible insecticide treatment for effective management of stem girdler in soybean. (6.57), in contrast to 28.65 in control. Even at 10 DAS, Chlorantraniliprole (4.59) and Fipronil (6.00) sustained lowest pest levels, while control peaked at 33.34. The present investigation demonstrating the superior effectiveness, persistence, and residual toxicity of selected insecticides against the girdle beetle is in strong conformity with earlier research on soybean stem girdler management. The prolonged suppression of Obereopsis brevis observed in the most efficacious treatments substantiates the findings of Bhamare et al. (2020) [2] , who reported that newer generation insecticidal molecules maintained significantly lower infestation levels for extended periods compared with conventional compounds and ensured protection even during later crop stages. A similar trend in comparative performance among chemical groups also corroborates the observations of Bokan et al. (2021) [3] , wherein certain insecticides exhibited rapid knock-down action followed by sustained residual control, while gradual pest resurgence occurred as residues declineda phenomenon likewise evident in the present study. Furthermore, the marked reduction in infestation shortly after spraying supports the conclusions of Raju et al. (2013) [4] , who emphasized that timely application during the active larval phase considerably enhances management efficiency against soybean stem borers and defoliators. In addition, the consistently lower pest incidence in treated plots relative to the untreated control agrees with the results of Patil and Phad (2014) [5] , who demonstrated that promising insecticides effectively minimized damage from stem fly and girdle beetle and thereby reduced potential yield losses.
Results and Discussion
Collectively, these concordant findings reinforce that judicious and timely application of effective insecticides constitutes a crucial component of reliable girdle beetle management in soybean.
References
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