Bioefficacy of Beauveria bassiana against different larval instars of Spodoptera litura on cabbage in laboratory conditions

Introduction

Cabbage is the third major vegetable crop primarily grown in the winter season and an important vegetable of the cole group. India occupies the first position in cauliflower, second in onion, and third in cabbage in the world. Cabbage is a rich source of vitamins A, B1, B2, C, K and it also contains minerals. It is used as salad, boiled vegetables and dehydrated vegetables as well as in cooked curries and pickles. It possesses both antioxidant and anticarcinogenic properties. However, the production of cabbage is confronted with numerous constraints. It is prone to several nutrient deficiencies, as well as to multiple insect pests and bacterial and fungal diseases. One of the major pests of cabbage is Spodoptera litura (Fabricius), (Lepidoptera: Noctuidae). It is a serious polyphagous pest in Asia, Oceania and the Indian subcontinent. The pest is infesting 150 species of agricultural crops belonging to 44 families universally (Kranthi et al., 2002) [6] , of which 40 species are known from India (Chari and Patel, 1972) [2] . The pest may cause severe damage, resulting in low productivity of cabbage when present in large numbers. Spodoptera litura causes excessive damage ranging from 26-100% by its vigorous defoliation (Dhir et al., 1992) [4] . The management of Spodoptera litura has become increasingly difficult all over the world, and the most commonly used insecticides are ineffective in controlling it. Spodoptera litura was the first lepidopteran to develop insecticide resistance in India (Srivastava and Joshi, 1965) [7] . In recent years, crop protection based on biological control of crop pests with microbial pathogens like viruses, bacteria, fungi and nematodes has been recognized as a valuable tool in pest management. Beauveria bassiana, causing disease in insects commonly called, 'white muscardine disease' is widely regarded as a potential bio control agent. Biopesticides clearly have a potential role to play in the development of IPM strategies. So there is a need to test Beauveria bassiana to be used in IPM of Spodoptera litura, remaining a major recurring pest requiring considerable control measures. In order to know the potential of Beauveria bassiana as one of the important inputs for safe and sustainable agriculture, studies were undertaken for its evaluation and selection for use in IPM of Spodoptera litura on cabbage.

Materials and Methods

Laboratory trials were conducted to test the bio efficacy of three commercial formulations of B. bassiana against Spodoptera litura. The larva of these insects were collected from Jawan, Aligarh, (U.P) and pure culture was raised in the laboratory. Commercial formulations, viz., Multiplex Baba, Green Beauveria, WAH were taken for this as detailed in Table 1. Conidial suspensions of these formulations @ 1 × 10 8 CFU / ml, 2 × 10 8 spores / ml, 2 × 10 8 CFU / g respectively (Table 1), and were prepared in distilled water containing 0.01% Cween 80. This concentration was more or less near the minimum recommended concentration for use on cabbage crops. Spore suspension of B. bassiana at four different concentrations, 1, 2, 3, and 4% was prepared and cabbage leaves were dipped in it for 30 seconds and tested for its efficacy on 1 st , 2 nd , 3 rd and 4 th instar larva of S. litura. Three replicates of 10 larvae each with a control were taken in plastic vials (4.5×12.0cm 2 ) lined with moistened cotton and filter paper above it to maintain humidity. The vials had screw caps having provision for proper aeration. Aseptic conditions were maintained throughout the experiment. Observations were recorded daily at 24-hour intervals on mortality and disease development till pupation and adult emergence. All experiments were conducted in BOD at 27±1°C and 70±5 per cent RH. Dead larvae were kept in a moist chamber for confirmation of mycosis. The experiments were repeated three times. The details of the experiment is mentioned in Table 2. Cumulative per cent mortality was calculated from 1 st , 3 rd , 7 th , and 14 th day, and data was subjected to one-way analysis of variance. The efficacy of different treatments was compared on 5 per cent level of significance. 2 Correlation coefficient 𝛘 2 Chi -square value Correlation coefficient 𝛘 2 Chi -square value

The results in Table 5 and 6 shows that Spodoptera litura first instar larva treated with WAH was more effective and LC50 value was 1.378 followed by Green Beauveria (2.024) and Multiplex Baba (7.579). In second instar treated larvae WAH was found to be most effective than other commercial formulations with LC50 value of 0.888 followed by Green Beauveria (3.32) and Multiplex Baba (3.649). However, the fungal formulations were least effective in third and fourth instar larvae. Multiplex Baba was effective than the rest with 4.573 and 6.956 LC50 values respectively. Lethal time (LT50) in 4 per cent concentration of green Beauveria was found to be 2.943 followed by WAH (8.33) and Multiplex Baba (10.064) when observed for first instar larvae. In second instar treated larvae LT50 value for 4 per cent concentration of Green Beauveria was 6.169 followed by WAH (6.75) and Multiplex Baba (7.5). However, in third and fourth instar larva these biopesticides were least effective with LT50 values of 16.42 and 17.48 for 4 per cent concentration of Multiplex Baba respectively.

Discussion

Studies pertaining to laboratory trials on bio efficacy revealed that all the larval stages of Spodoptera litura were not equally susceptible to the infection of Beauveria bassiana but the fungus was found more pathogenic to early instar. Higher susceptibility to younger stages and reduced susceptibility to older stages if considered together reveal that the younger stages when treated die at once due to their very small and soft body parts. Younger larval stages thus have an increased probability of acquiring an infection. Late larval stages, on the other hand, have reduced food intake and a thicker cuticle and thus it is less likely that spores would enter or penetrate their body. The present studies are conformity with the findings of Hung and Boucias (1992) [5] who tested the fungi against the leaf worm and beet army worm showing that the fungus B. bassiana (Balsamo), Vuillemin caused a high mortality to the insect at earlier stages. Asi et al., (2013) [1] reported virulence potential of the entomopathogenic fungi varied with different biological stages of the Spodoptera litura.

Conclusion

Beauveria bassiana was found to be highly effective against various larval instars of Spodoptera litura on cabbage. The fungus produced significant mortality rates throughout all larval stages, with younger instars showing the greatest efficacy. These findings indicate that B. bassiana could be an effective bio control agent for managing S. litura infestations on cabbage, providing an environmentally acceptable alternative to conventional pesticides. More study is needed to improve application strategies and develop effective B. bassiana-based products for sustainable pest management in cabbage agriculture.

Acknowledgement

AcknowledgmentsFinancial support for this research was graciously provided by the Department of Plant Protection, Faculty of Agricultural Sciences, Aligarh Muslim University, Aligarh, Uttar Pradesh, India. The authors declare that they have no conflict of interest that influences the work reported in this paper.

References

1. Asi MR, Bashir MH, Afzal M, Zia K, Akram M. Potential of entomopathogenic fungi for biocontrol of Spodoptera litura Fabricius (Lepidoptera: Noctuidae). J Anim Plant Sci. 2013;23(3):913-918.
2. Chari MS, Patel NG. Efficacy of some newer insecticides against the tobacco leaf eating caterpillar, Spodoptera litura (Fabricius). Indian J Entomol. 1972;34:261-262.
3. Cohen WM, Levinthal DA. Absorptive capacity: A new perspective on learning and innovation. Adm Sci Q. 1990 Mar;35(1):128-152.
4. Dhir SK, Dhir S, Widholm JM. Regeneration of fertile plants from protoplasts of soybean (Glycine max L. Merr.): genotypic differences in culture response. Plant Cell Rep. 1992 Jun;11:285-289.
5. Hung SY, Boucias DG. Influence of Beauveria bassiana on the cellular defense response of the beet armyworm, Spodoptera exigua. J Invertebr Pathol. 1992 Sep;60(2):152-158.
6. Kranthi KR, Jadhav DR, Kranthi S, Wanjari RR, Ali SS, Russell DA. Insecticide resistance in five major insect pests of cotton in India. Crop Prot. 2002 Jul;21(6):449-460.
7. Srivastava BK, Joshi HC. Occurrence of resistance to BHC in Prodenia litura Fabr. (Lepidoptera: Noctuidae). Indian J Entomol. 1965;27(1):102-104.