Bio-efficacy of Bacillus thuringiensis formulations against lepidopteran pests of cabbage

Introduction

Cabbage (Brassica oleracea var. capitata L.) is an important vegetable crop of the family Brassicaceae and is widely cultivated for its nutritional and economic value. In India, cabbage was cultivated over 442.33 thousand hectares with a production of 10,431.70 thousand metric tonnes during 2023-24. In Maharashtra, the crop occupied 7.75 thousand hectares with a production of 101.37 thousand metric tonnes during the same period (Anonymous, 2024) [1] . Cabbage is attacked by several insect pests, of which lepidopteran pests are among the most important constraints to production. The diamondback moth (Plutella xylostella L.) is considered one of the most destructive pests of cabbage and other cruciferous crops, while the tobacco caterpillar (Spodoptera litura Fabricius) is an important defoliating pest that can cause substantial damage to cabbage foliage. Larval feeding results in loss of leaf area and can consequently reduce crop growth, marketable yield and economic returns. Management of these pests has largely depended on synthetic insecticides. However, their repeated and indiscriminate use has resulted in problems such as development of insecticide resistance, pest resurgence, pesticide residues and environmental contamination. The development of resistance in P. xylostella to several groups of insecticides has further complicated its management. These limitations emphasize the need for effective and sustainable alternatives for the management of lepidopteran pests in cabbage. Bacillus thuringiensis (Bt) is an important microbial insecticide used for the management of lepidopteran larvae. It produces insecticidal crystal (Cry) proteins that become active after ingestion by susceptible larvae and disrupt the midgut epithelium, ultimately causing larval mortality (Nester et al., 2002) [6] . Its target-specific insecticidal activity has made Bt an important component of sustainable insect pest management programmes.

At Dr. Panjabrao Deshmukh Krishi Vidyapeeth (PDKV), Akola, indigenous Bt strains have been developed and evaluated under laboratory conditions against insect pests. However, their field bio-efficacy against major lepidopteran pests of cabbage has not been adequately evaluated. Further, the performance of Bt under field conditions may vary with the formulation used. Wettable powder (WP) and suspension concentrate (SC) are important formulation types that can influence product stability, application and field performance. Therefore, the present investigation was undertaken to evaluate the field bio-efficacy of PDKV Bacillus thuringiensis formulations against the two important lepidopteran pests of cabbage, namely diamondback moth (Plutella xylostella L.) and tobacco caterpillar (Spodoptera litura Fabricius), and to assess the comparative performance of different Bt formulations under field conditions.

Materials and Methods

A field experiment was conducted during the Rabi season of 2025-26 at the experimental field of the Department of Vegetable Science, Dr. Panjabrao Deshmukh Krishi Vidyapeeth, Akola, Maharashtra, India, to evaluate the bioefficacy of Bacillus thuringiensis (Bt) formulations against major lepidopteran pests of cabbage. The experiment was laid out in a Randomized Block Design (RBD) with 25 treatments and two replications. Cabbage variety Royal Ball BC-79 was used for the experiment. The gross plot size was 2.7 × 1.5 m and the net plot size was 1.8 × 1.2 m. The crop was planted at a spacing of 60 cm between rows and 45 cm between plants. Transplanting was carried out on 17 December 2025. The experiment comprised different PDKV Bt strains formulated as 25% wettable powder (WP) and 75% suspension concentrate (SC). The WP and SC formulations were applied at 1 kg ha⁻¹ and 1 L ha⁻¹, respectively. Delfin @ 1 kg ha⁻¹ was included as a standard Bt formulation, while Quinalphos 25% EC @ 1 L ha⁻¹ was used as a chemical insecticide treatment. An untreated control was also maintained. The complete treatment structure consisted of 25 treatments.

Preparation of Bt formulations

Local Bacillus thuringiensis isolates, previously isolated and screened for insecticidal activity at the Department of Entomology, Dr. PDKV, Akola, were subcultured and maintained on Luria broth medium. The PDKV Bt strains were subsequently developed into wettable powder (WP) and suspension concentrate (SC) formulations at the Department of Entomology. The WP formulation was prepared following the method described by Marzaban et al. (2021) [5] , whereas the SC formulation was prepared according to the method of Vimla Devi et al. (2014) [8] . The prepared formulations were used for field evaluation against Plutella xylostella and Spodoptera litura on cabbage. Three applications of the respective treatments were made at 15-day intervals. The first spray was applied when the pest population reached the economic threshold level (ETL), followed by two subsequent applications at 15-day intervals. The bio-efficacy of the treatments was evaluated against diamondback moth (Plutella xylostella) and Spodoptera litura. Pre-treatment observations were recorded before each spray, while post-treatment observations were recorded at 7 and 14 days after treatment (DAT).

For both Plutella xylostella and Spodoptera litura, five plants were selected randomly from each treatment plot for recording larval population. Pre-treatment observations were recorded before each spray, while post-treatment observations were recorded at 7 and 14 days after treatment (DAT). The number of larvae present on the selected plants was recorded, and the mean larval population per plant was calculated for statistical analysis.

Results and Discussion

Bio-efficacy of Bt formulations against diamondback moth, Plutella xylostella L The field evaluation revealed significant differences among the treatments in their ability to suppress the larval population of Plutella xylostella. After three sprays, the cumulative mean larval population varied considerably among the treatments. The untreated control recorded the highest larval population of 5.30 larvae plant⁻¹, whereas the lowest population was recorded in the chemical standard T 24 (Quinalphos 25% EC) with 1.58 larvae plant⁻¹. Among the Bt formulations, T 21 (PDKV-SY-4 25% WP) was the most effective, recording 1.78 larvae plant⁻¹ and 66.42% reduction over the untreated control. It was followed by T12 (PDKV-SGd-1 75% SC) with 1.95 larvae plant⁻¹ (63.21% reduction), T 23 (commercial Bt formulation, Delfin) with 2.08 larvae plant⁻¹ (60.75% reduction) and T 22 (PDKV-SY-4 75% SC) with 2.27 larvae plant⁻¹ (57.17% reduction). The remaining Bt formulations produced progressively lower levels of suppression. The superior performance of T 21 indicates that PDKV-SY-4 25% WP had the highest larvicidal efficacy among the Bt formulations tested against P. xylostella. The difference in performance among formulations may be associated with variation in the biological activity and formulation characteristics of the Bt preparations, which can influence deposition, persistence and ingestion by the larvae. The effectiveness observed in the present study is consistent with earlier findings that Bt formulations can substantially suppress P. xylostella populations on cabbage. Voltukhov (1975) [10] reported effective suppression of DBM by a Btbased formulation, while Krishnaiah et al. (1981) [3] demonstrated that Dipel provided effective control comparable with conventional insecticides. Similarly, Raut and Simon (2010) [7] reported significant reduction of DBM infestation with B. thuringiensis var. kurstaki under field conditions. The present findings are also supported by field and laboratory studies demonstrating the effectiveness of Bt against DBM. Commercial Bt formulations have been reported to effectively reduce P. xylostella larval populations and increase cabbage yield, while different Bt formulations have shown differences in their relative efficacy. Thus, the present results demonstrate that PDKV-SY-4 25% WP has promising potential for the management of Diamondback moth (P. xylostella) under field conditions.

Bio-efficacy of Bt formulations against Spodoptera litura Fabricius

Significant differences were also observed among the treatments in suppressing the larval population of Spodoptera litura. The cumulative mean larval population in the untreated control was 2.90 larvae plant⁻¹. The chemical standard T 24 (Quinalphos 25% EC) recorded the lowest population of 0.77 larvae plant⁻¹ (73.45% reduction over control). Among the Bt formulations, T5 (PDKV-SA-20 25% WP) and T21 (PDKV-SY-4 25% WP) were equally effective, each recording 0.97 larvae plant⁻¹ and 66.55% reduction over the untreated control. They were followed by T11 (PDKV-SGd-1 25% WP) with 0.98 larvae plant⁻¹ (66.21% reduction), T12 (PDKV-SGd-1 75% SC) with 1.00 larvae plant⁻¹ (65.52% reduction), T6 (PDKV-SA-20 75% SC) with 1.02 larvae plant⁻¹ (64.83% reduction), T23 (Delfin) with 1.05 larvae plant⁻¹, and T 22 (PDKV-SY-4 75% SC) with 1.08 larvae plant⁻¹. The comparable performance of T 5 and T 21 indicates that both formulations had strong activity against S. litura. The results further show that the response of S. litura was not identical to that of P. xylostella, indicating that Bt formulations may differ in efficacy according to the target pest. This variation is biologically relevant because susceptibility to Bt formulations can differ among lepidopteran species and larval stages. Earlier studies included in the present review also support the activity of Bt against S. litura. Venkadasubramanian and David (1999) also reported effective suppression of S. litura by commercial Bt products, while Martinez et al. (2004) [4] found differences in the relative performance of Bt formulations against S. litura. The present field results therefore confirm that Bt formulations, particularly PDKV-SA-20 25% WP and PDKV-SY-4 25% WP, can substantially suppress S. litura populations on cabbage. Their performance against this pest demonstrates the potential of native Bt formulations as biological tools for management of lepidopteran pests.

Effect of Bt formulations on cabbage yield

Significant differences were observed among treatments with respect to cabbage head yield. The untreated control produced the lowest yield of 158.02 q ha⁻¹. The highest yield was recorded in T 24 (Quinalphos 25% EC) with 294.63 q ha⁻¹, followed by T 21 (PDKV-SY-4 25% WP) with 292.35 q ha⁻¹, representing an 85.01% increase over the untreated control. Other treatments producing comparatively high yields included T 11 (PDKV-SGd-1 25% WP) with 284.44 q ha⁻¹, T 12 (PDKV-SGd-1 75% SC) with 284.20 q ha⁻¹, T22 (PDKV-SY-4 75% SC) with 269.63 q ha⁻¹, T23 (Delfin) with 259.75 q ha⁻¹, T 5 (PDKV-SA-20 25% WP) with 259.63 q ha⁻¹ and T6 (PDKV-SA-20 75% SC) with 256.05 q ha⁻¹. The treatment effect on yield was statistically significant The higher yield obtained from Bt-treated plots can be attributed primarily to reduced larval feeding and consequently lower crop damage during head formation and development. The performance of T 21 was particularly noteworthy because it combined effective suppression of both major lepidopteran pests with low head damage and high cabbage yield. Although the chemical standard produced the numerically highest yield, the yield obtained with T 21 was statistically comparable with several of the better-performing treatments according to the experimental comparison. The present results are in agreement with earlier reports that Bt application can reduce lepidopteran infestation and improve cabbage yield. Voltukhov (1975) [10] reported a 17-18% increase in cabbage yield following application of a Btbased formulation against P. xylostella, while Justin et al. (1990) [2] observed improved crop yield with Bt treatment. Field evaluation of Bt formulations against DBM has also demonstrated increased cabbage yield following effective pest suppression. Taken together, the results demonstrate that the tested Bt formulations differed considerably in their field performance against the two major lepidopteran pests of cabbage. PDKV-SY-4 25% WP (T 21 ) emerged as the most consistently effective Bt formulation, producing the lowest cumulative DBM population among the Bt treatments, a high level of suppression of S. litura, the lowest Bt-associated head damage and a high cabbage yield of 292.35 q ha⁻¹. For S. litura, PDKV-SA-20 25% WP (T 5 ) and PDKV-SY-4 25% WP (T 21 ) were equally effective based on cumulative larval population. The overall pattern indicates that effective suppression of P. xylostella and S. litura by Bt formulations resulted in reduced head damage and consequently greater cabbage yield. Therefore, the present investigation demonstrates the potential of selected PDKV Bt formulations, particularly PDKV-SY-4 25% WP, for managing important lepidopteran pests of cabbage under field conditions.

Conclusion

The study demonstrated the efficacy of Bacillus thuringiensis (Bt) formulations against major lepidopteran pests of cabbage, Plutella xylostella and Spodoptera litura. Among the indigenous formulations, PDKV-SY-4 25% WP @ 1 kg ha⁻¹ was the most effective, recording lower pest infestation and higher head yield, comparable with Delfin and quinalphos 25% EC. Economically, it was the most promising indigenous Bt formulation. Thus, PDKV-SY-4 25% WP can be considered a potential Bt-based component of integrated management of lepidopteran pests in cabbage.

Acknowledgement

AcknowledgementsThe authors are thankful to the Head, Department of Entomology and the Associate Dean, Post Graduate Institute, Dr. PDKV, Akola (MS) for providing all the basic facilities required for conduction of the experiment.

References

1. Anonymous. Horticultural statistics at a glance 2024. Department of Agriculture and Farmers Welfare, Government of India; 2024.
2. Justin CGL, Rabindra RJ, Jayaraj S. Bacillus thuringiensis Berliner and some insecticides against the diamondback moth, Plutella xylostella (L.) on cauliflower. Journal of Biological Control. 1990;4(1):4043.
3. Krishnaiah N, Mohan M, Prasad VG. Efficacy of Bacillus thuringiensis for the control of lepidopterous pests of vegetable crops. Entomon. 1981;6(2):87-94.
4. Martinez C, Porcar M, Lopez A, Dercudoro IR, PerezLlurena FJ, Caballero P. Characterization of a Bacillus thuringiensis strain with a broad spectrum of activity against lepidopteran insects. Entomologia Experimentalis et Applicata. 2004;111(1):71-77.
5. Marzban R, Babaei J, Kalantari M, Saberi F. Preparation of wettable powder formulation of Bacillus thuringiensis KD2. Journal of Applied Biological Sciences. 2021;15(3):285-293.
6. Nester EW, Thomashow LS, Metz M, Gordon M. 100 years of Bacillus thuringiensis: A critical scientific assessment. Washington, DC: American Society for Microbiology; 2002. doi:10.1128/AAMCol.16Nov2002.
7. Raut A, Simon S. Comparative efficacy of some biopesticides and insecticides against diamondback moth, Plutella xylostella (L.) on cabbage in Allahabad, U.P. Trends in Biosciences. 2010;3(2):174-175.
8. Vimala Devi PS, Vineela V. Suspension concentrate formulation of Bacillus thuringiensis var. kurstaki for effective management of Helicoverpa armigera on sunflower (Helianthus annuus). Biocontrol Science and Technology. 2015;25(3):329-336.
9. Venkadasubramaniam V, David PMM. Insecticidal toxicity of commercial Bacillus thuringiensis (Berliner) products in combination with botanicals to Spodoptera litura (Fabricius) and Helicoverpa armigera (Hübner). Journal of Biological Control. 1999;13:85-92.
10. Voltukhov VA. Economic evaluation of the chemical and biological methods. Zashchita Rastenii. 1975;6:29.
11. Marzban R, Babaei J, Kalantari M, Saberi F. Preparation of wettable powder formulation of Bacillus thuringiensis KD2. J Appl Biol Sci. 2021;15(3):285-293.
12. Vimala Devi PS, Vineela V. Suspension concentrate formulation of Bacillus thuringiensis var. kurstaki for effective management of Helicoverpa armigera on sunflower (Helianthus annuus). Biocontrol Sci Technol. 2015;25(3):329-336. doi:10.1080/09583157.2014.977846.