Bioefficacy of biorational insecticides for the management of pod borer, (Helicoverpa armigera) on pigeonpea (Cajanus cajan L.)

Introduction

Pigeonpea [Cajanus cajan (L.) Millspaugh] is one of the major kharif pulse crops cultivated in India and is popularly referred to as red gram, tur, or arhar. It is considered to have originated in India and is extensively grown across tropical and subtropical regions due to its wide adaptability and significance in pulse-based cropping systems. The crop possesses high nutritional value, with seeds containing approximately 18 to 25 per cent protein, thereby making an important contribution to food and nutritional security (Saxena, 2008; Upadhyaya et al., 2013) [9,11] . In Chhattisgarh, pigeonpea is a major rainfed pulse crop and holds a vital position in the state's agricultural production system. During 2022-23, it was cultivated over an area of 39.87 thousand hectares, producing 27.55 thousand tonnes with an average productivity of 467 kg/ha. These figures emphasize the crop's considerable importance under the rainfed agro-climatic conditions of the state (Anonymous, 2024) [2] . The pod borer complex is regarded as one of the most serious constraints limiting pigeonpea production. More than 250 insect species have been recorded on pigeonpea; however, only a few are of major economic significance. These include the gram pod borer, Helicoverpa armigera (Hubner), plume moth, Exelastis atomosa (Walsingham), pod fly, Melanagromyza obtusa (Malloch) and occasionally Maruca vitrata, all of which together inflict considerable damage on the crop (Lal, 1998; Patil et al., 1990) [6,8] . Among these insect pests, H. armigera is recognized as the most destructive and constitutes a major biotic constraint in pigeonpea cultivation, causing substantial yield losses by feeding on flower buds, flowers and developing pods (Lal, 1998) [6] . Under favourable environmental conditions, these pod borers can inflict severe damage on pigeonpea, resulting in substantial yield reduction. Their management has become increasingly challenging due to the frequent and indiscriminate application of chemical insecticides, which has contributed to the development of insecticide resistance, pest resurgence, outbreaks of secondary pests and adverse effects on human health as well as the environment (Anonymous, 2021) [1] . Consequently, the continuous use of chemical insecticides is no longer regarded as a sustainable approach to pest management. Greater attention is now being directed towards environmentally safer alternatives, including biorational insecticides, microbial pesticides and botanical products, for effective pest control. In view of these considerations, the present investigation was undertaken to evaluate the bioefficacy of selected biorational insecticides against H. armigera in pigeonpea.

Materials and Methods

The present investigation was conducted at Raj Mohini Devi College of Agriculture and Research Station, Ambikapur, Chhattisgarh during Kharif 2024-25 to evaluate the bioefficacy of biorational insecticides against Helicoverpa armigera infesting pigeonpea. The experiment was conducted in a randomized block design with three replications and seven treatments. The pigeonpea variety CG Arhar-1 was grown in plots of 4 m × 5 m size, maintaining a spacing of 50 cm between rows and 25 cm between plants. The treatments included Beauveria bassiana, Metarhizium anisopliae, Bacillus thuringiensis, Azadirachtin (0.3% EC), Paecilomyces lilacinus, Emamectin benzoate (5% SG) and untreated control. The crop was sprayed three times, at 50 per cent flowering, pod initiation and 50 per cent pod formation stage. Spray solutions were prepared as per recommended doses and applied with a knapsack sprayer. Observations on the larval population of H. armigera were recorded from randomly selected plants one day before each spray and subsequently at 3, 7 and 12 days after every spray. Pod and grain damage were assessed using 100 randomly selected pods collected from the four central rows of each experimental plot at the green pod and crop maturity stages. The percentage of pod and grain damage caused by H. armigera was determined based on the number of damaged pods and grains observed in each plot. Grain yield was recorded separately for each plot and subsequently expressed as quintals per hectare. Yield increase over control was calculated by comparing the yield of each treatment with the untreated control. Economic analysis was done on the basis of market price of pigeonpea and cost of treatments. Net return and incremental costbenefit ratio were calculated accordingly. The data on larval population and percentage damage were transformed prior to statistical analysis wherever required. The significance of treatment effects was tested at 5 per cent level of probability.

Results and Discussion

Bioefficacy of biorational insecticides against larval population of H. armigera in pigeonpea

The data on the bioefficacy of different biorational insecticides against the larval population of Helicoverpa armigera in pigeonpea are presented in [4] reported the lowest H. armigera larval population with Bacillus thuringiensis var. kurstaki (1.85 larvae/plant), followed by Beauveria bassiana (2.12 larvae/plant), compared with the untreated control (4.67 larvae/plant). Similarly, Meena et al. (2021) [7] found Emamectin benzoate (5% SG) to be the most effective treatment, followed by Bacillus thuringiensis and Metarhizium anisopliae, with the minimum larval population of 0.96 larvae/plant.

Figures in parenthesis are

Bioefficacy of various treatments against pod and grain damage due to H. armigera in pigeonpea

The data on pod and grain damage caused by H. armigera (Table 3) revealed that all the treatments significantly reduced damage compared with the untreated control. Emamectin benzoate (5% SG) recorded the lowest pod damage (4.68%) and grain damage (10.34%), whereas the untreated control registered the highest pod damage (18.65%) and grain damage (24.75%). Among the biorational insecticides, Bacillus thuringiensis proved to be the most effective treatment after the standard chemical check, recording the lowest pod damage (7.31%) and grain damage (11.27%). This was followed by Beauveria bassiana, which recorded (7.82%) pod damage and (13.49%) grain damage, Azadirachtin 0.3% EC with (8.60%) pod damage and (12.61%) grain damage, Metarhizium anisopliae with (8.46%) pod damage and (14.08%) grain damage and Paecilomyces lilacinus with (9.27%) pod damage and (15.15%) grain damage. The present results are also supported by the findings of Kumar and Nath (2018) [5] , who reported that Emamectin benzoate (5% SG) was highly effective in reducing larval population of H. armigera with minimum pod damage (8.42%), followed by B. thuringiensis (12.36%) and Azadirachtin 0.03% EC (15.27%), as compared to untreated control (32.48%).

Effect of biorational insecticides on grain yield and economics in pigeonpea

The grain yield and economic analysis (Table 3) revealed that all the treatments were superior to the untreated control, which recorded a grain yield of (9.20 q/ha.) Emamectin benzoate (5% SG) recorded the highest grain yield of (17.05 q/ha), maximum increase in yield over control of (7.85 q/ha), highest net return of Rs. (62,440/ha) and maximum incremental cost-benefit ratio of (1:2.7). Among the biorational insecticides, Bacillus thuringiensis emerged as the most effective and economical treatment after the standard chemical check by recording grain yield of (15.77 q/ha), increase in yield over control of (6.57 q/ha), net return of Rs. (44,666/ha) and ICBR of (1:2.0). It was followed by Azadirachtin (0.3% EC) with grain yield of (14.68 q/ha), yield increase of (5.48 q/ha), net return of Rs. (35,644/ha) and ICBR of (1:1.7). These findings indicated that Bacillus thuringiensis was the most promising biorational insecticide for the management of H. armigera in pigeonpea under field conditions. The present observations are in close agreement with earlier studies. Choudhary and Singh (2017) [3] , who revealed that Emamectin benzoate (5% SG) recorded the highest grain yield (18.42 q/ha), followed by Bacillus thuringiensis (16.85 q/ha) and Azadirachtin 0.3% EC (15.73 q/ha), compared to untreated control (10.24 q/ha). Similarly, Sharma and Singh (2018) [10] , also reported that Emamectin benzoate (5% SG) as the most effective treatment, producing the highest grain yield (19.84 q/ha), while Bacillus thuringiensis and Beauveria bassiana also performed well over control.

Conclusion

Among the biorational insecticides evaluated, Bacillus thuringiensis emerged as the most effective treatment after the standard chemical check, Emamectin benzoate (5% SG), as it recorded the lowest pest population, minimum pod and grain damage, highest grain yield and maximum incremental cost-benefit ratio among the biopesticidal treatments. Hence, Bacillus thuringiensis can be considered an effective biorational option for the management of Helicoverpa armigera in pigeonpea.

Acknowledgement

AcknowledgementsThe first author expresses his heartfelt gratitude to Major Advisor, Head of Section (Entomology), all the Advisory member, Staff members, Dean, RMD CARS Ambikapur and Head of Department (Entomology), COA Raipur for their excellent guidance, suggestions and regular encouragement during the course of investigation.

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