Evaluation of newer insecticides against shoot fly, Atherigona Pulla (diptera: Muscidae) in little Millet

Introduction

Little millet (Panicum sumatrense) (miliare) (Family: Poaceae) mainly grown in arid and semi-arid regions of Asia and Africa, where it serves as a staple food for several communities. It is known for its resilience to drought and poor soil conditions (Sharma et al., 2016) [18] . The highly diverse agro-ecosystem in which, millet-growing areas directly and indirectly affects grain yield through various biotic and abiotic factors. A survey on insectpest incidence on millets indicated that crops are affected by 50 to 55 different insect-pest species across various regions and seasons, from sowing to harvesting and storage (Nageshchandra and Ali, 1983 [14] . Within this complex pest landscape, shoot flies from the genus Atherigona (Muscidae) are particularly harmful, leading to considerable yield loss, especially in little millet during the 4 to 5 leaf stage (Nageshchandra and Ali, 1983 [14] , Kumar et al., 2019) [12] . Whereas Ganiger et al. 2024 [6] , worked on taxonomic identification of maggot and adult stages of kodomillet shoot fly, Atherigona simplex. For instance, sorghum and pearl millet are widely cultivated in Africa and India, respectively, both regions face serious insect pest challenges. Among these pests, the shoot fly is particularly damaging and can lead to substantial crop losses (Gahukar and reddy, 2019) [5] . Kishore (1996) [10] reported 116 pests that infest pearl millet, in which major pest includes shoot fly (Atherigona approximata), stem borer (Chilo partellus), pose significant challenges in management at field level. Shoot flies typically begin to attack crops in July, with infestations becoming more severe in late-sown crop and persisting throughout the Kharif season. In the Rabi season, infestations are relatively lower compared to Kharif. The maggots enter the shoot and sever the growing point, leading to the distinct symptom known as dead-heart (Kahate et al., 2014) [8] . Among small millets, little and proso millets are particularly hard hit by shoot fly infestations, which can cause up to 60 per cent damage and result in a 90 per cent yield loss. Late-sown Kharif crops are more severely affected. Their high fecundity and short life cycle allow their populations to increase rapidly (Jagadish et al., 1995) [7] . Chemical management is a vital strategy for controlling pest populations, especially when quick intervention is necessary to reduce damage. Effective insecticides can significantly help in managing shoot fly infestations. There appears to be limited research on this subject, as information about shoot fly infestations in little millet crop is quite sparse. In contrast, there is a significant depth of work published on related species of shoot fly affecting other millets, particularly sorghum. Choosing the right chemical agents is critical for successful pest management.

Material and Methods

For the management of shoot fly in little millet, the experiment was conducted at the ZARS, UAS, GKVK, Bengaluru, during Kharif 2023 and 2024. For this experiment, the little millet variety TNAU-186 was sown with a spacing of 30 × 10 cm in a plot size of 3 × 4 m. The field experiment was laid out in Randomized Complete Block Design (RCBD) with ten treatments and three replications comprising different insecticides along with untreated control.

Observations recorded:

The seed treatment was done with insecticide before sowing the crop and the spraying was initiated at 7 days after germination of the crop. The per cent of dead-heart was recorded at one day before spraying and 3, 5 and 10 days after the spray. After every observation, recorded plants are tagged and these tagged plants won't be considered for further next observations to follow the random sampling method. Finally, harvesting yield was recorded. The per cent dead-heart was calculated by using the following formula,

Statistical analysis

The statistical analysis of the data obtained from management trials was done by the Analysis of Variance (ANOVA). After analysis, data were accommodated in the table as per the needs of the objective for the interpretation of results. The differences in the observations among the different treatments were compared by following Duncan's Multiple Range Test (DMRT). The interpretation of data was done by using the critical difference value calculated at the 0.05 probability level.

Results and discussion

The management of shoot fly in little millet (TNAU-186) was studied at the ZARS, UAS, GKVK, Bengaluru, during Kharif 2023 and 2024. During research period eight newer insecticides were tested to reduce the infestation of deadheart in little millet. The management of shoot fly in little millet during Kharif 2023 revealed significant differences in dead-heart incidence across treatments at various intervals. One day before spraying (1 DBS), the lowest dead-heart percentage was recorded in imidacloprid 48 FS @ 12ml/kg of seeds (T1) (11.11%) followed by cyantraniliprole 19.8%+thiamethoxam 19.8% FS @ 4ml/kg of seeds (T3) (12.22%) and thiamethoxam 30 FS @ 10ml/kg of seeds (T2) (13.33%). At 3 days after spraying (3 DAS), imidacloprid 48 FS @ 12 ml/kg of seeds (T1) continued to exhibit the lowest dead-heart percentage (13.33%), followed by cyantraniliprole 19.8%+thiamethoxam19.8% FS @ 4 ml/kg of seeds (T3) (14.45%) and thiamethoxam 30 FS @ 10 ml/kg of seeds (T2) (15.56%), while untreated control recorded the highest damage (25.56%). At 5 DAS, lamdacyhalothrin 5% EC @ 1 ml/l (T6) showed the least incidence (13.33%), followed by imidacloprid 48 FS @ 12 ml/kg of seeds (T1) (15.56%) and cyantraniliprole 19.8%+thiamethoxam19.8% FS @ 4 ml/kg of seeds (T3) (16.67%), with untreated control recording the highest infestation (26.67%). By 10 DAS, lamdacyhalothrin 5% EC @ 1 ml/l (T6) maintained the lowest dead-heart percentage (10.00%), followed by difenthiuron 50 WP @ 1.25 g/l (T8) (12.22%), whereas untreated control recorded the maximum damage (28.89%).

The pooled mean dead-heart of 1 DBS, 3, 5 and 10 DAS ranged from 14.45 to 26.11 per cent with imidacloprid 48 FS @ 12 ml/kg of seeds (T1) (14.45%) being superior over other treatments and on par with cyantraniliprole 19.8%+thiamethoxam19.8% FS @ 4 ml/kg of seeds (T3) (15.84%) and lamdacyhalothrin 5% EC @ 1 ml/l (T6) (16.95%). The least control was achieved in emamectin benzoate 5% SG @ 0.4 g/l (T7) (22.22%) besides untreated check (26.11%).

The management of shoot fly in little millet during Kharif 2024 revealed significant differences in dead-heart incidence across treatments at various intervals. One day before spraying (1 DBS), imidacloprid 48 FS @ 12ml/kg of seeds (T1) recorded the lowest dead-heart percentage (12.22%), followed by cyantraniliprole 19.8%+thiamethoxam 19.8% FS @ 4ml/kg of seeds (T3) (15.56%) and thiamethoxam 30 FS @ 10ml/kg of seeds (T2) (16.67%). At 3 DAS, imidacloprid 48 FS @ 12 ml/kg of seeds (T1) again showed the least damage (14.45%), followed by cyantraniliprole 19.8%+thiamethoxam19.8% FS @ 4 ml/kg of seeds (T3) (16.67%), while untreated control had the highest damage (33.33%). At 5 DAS, lamdacyhalothrin 5% EC @ 1 ml/l (T6) recorded the lowest dead-heart incidence (14.44%), followed by imidacloprid 48 FS @ 12 ml/kg of seeds (T1) (16.67%) and difenthiuron 50 WP @ 1.25 g/l (T8) (17.78%). By 10 DAS, lamdacyhalothrin 5% EC @ 1 ml/l (T6) remained most effective (11.11%), followed by difenthiuron 50 WP @ 1.25 g/l (T8) (12.22%), while untreated control had the maximum infestation (25.56%). The pooled mean dead-heart of 1 DBS, 3, 5 and 10 DAS ranged from 15.56 to 33.89 per cent with imidacloprid 48 FS @ 12 ml/kg of seeds (T1) (15.56%) being superior over other treatments and on par with cyantraniliprole 19.8%+thiamethoxam19.8% FS @ 4 ml/kg of seeds (T3) (18.06%) and thiamethoxam 30 FS @ 10 ml/kg of seeds (T2) (19.72%). The least control was achieved in thiamethoxam 25 WG @ 0.3 g/l (T5) (26.11%) besides untreated check (33.89%). Present findings are comparable to the results of Birangal et al. (2017) [3] and Daware et al. (2012) [4] , who reported that result on yield, plant height and their economics revealed that imidacloprid 48% FS at 10 ml/kg seed followed by spray of quinalphos 25% EC at 2 ml/l proved the most effective treatment. According to Biradar (2015) [2] , seeds treated with imidacloprid 70 WS (5 g/kg) found superior by recording 0.73 eggs/plant and significantly least per cent dead-hearts (14.83%) due to shoot fly. Highest yield was also recorded in this treatment (28.57 q/ha). Sonalkar et al. (2018) [19] , revealed that treating seeds with imidacloprid 48 FS, seed treatment at 12 ml/kg seeds in sorghum was significantly the most effective method against shoot fly. Patra et al. (2013) [15] observed that the maize crop damaged by major pests resulted in loss estimated at 8.5-21.75 per cent. Thus, seed treatment with combination of thiamethoxam (19.8 w/w) + cyantraniliprole (19.8 w/w) @ 6ml/kg can be recommended as a new combination against A. soccata in sorghum, with thiamethoxam 30 FS @ 10 ml/kg as a good option. Saxena et al. (2023) [17] reported that seed treated with thiamethoxam 30 FS, fipronil 5 SC and chlorantraniliprole 18.5 SC recorded better germination and yield compared to control. According to Wadghule (2005) [20] ; Balkai (2007); Kumar and Prabhuraj (2007) [11] , seed plots treated with thiamethoxam produced greater grain yields. Kumar and Tiwana (2018) [13] revealed the superiority of seed treatment with thiamethoxam 30 FS @ 10 ml per kg seed and closely followed by fipronil @ 10 ml per kg seed and gaucho @ 7ml per kg seed (7.71, 8.79 and 9.47% Dead-heart, respectively). Sandhu, (2016) [16] , suggested that seed treatment with thiamethoxam 30 FS @ 5 ml/kg seed and imidacloprid 600 FS @ 7 ml/kg seed were effective in reducing shoot fly incidence. Khandare et al. (2014) [9] , suggested that sorghum seed treatment provided highest germination per centage (92%) as observed in the seed treatment with thiamethoxam 35 FS @ 5 ml/kg seed and minimum numbers of dead-hearts (9.56%) were found on thiamethoxam 35 FS @ 5 ml/kg seed as compared to control (51.28 %).

The most effective treatments across Kharif 2023 and Kharif 2024 were imidacloprid 48 FS, achieving the highest reduction in dead-heart percentage (49.98%), followed by cyantraniliprole 19.8%+thiamethoxam 19.8% FS (43.50%) and thiamethoxam 30 FS (37.97%), while lamdacyhalothrin 5% EC also demonstrated notable effectiveness with a reduction rate of 37.95 per cent, positioning it among the moderately effective options.

Conclusion

The two-year field evaluation during Kharif 2023 and 2024 clearly demonstrated that shoot fly infestation in little millet (TNAU-186) can be effectively managed through appropriate seed treatment and foliar insecticide applications. Imidacloprid 48 FS @ 12 ml/kg of seeds consistently recorded the lowest pooled dead-heart incidence across both seasons, indicating its superiority and reliability. Cyantraniliprole 19.8% + thiamethoxam 19.8% FS and lamdacyhalothrin 5% EC were found to be statistically on par with imidacloprid and provided effective suppression at later crop stages. Difenthiuron 50 WP also showed promising performance, particularly at 10 DAS. In contrast, emamectin benzoate and thiamethoxam 25 WG were comparatively less effective, though better than the untreated control. The untreated check consistently registered the highest dead-heart incidence, confirming severe shoot fly pressure. Hence, imidacloprid seed treatment, alone or in combination with effective foliar sprays, can be recommended for sustainable management of shoot fly in little millet under field conditions.

Acknowledgement

AcknowledgementThe authors sincerely thank the Dept. of Agri. Entomology, University of Agricultural Sciences, Bengaluru, for providing the necessary facilities and support to conduct the present research. We express our gratitude to the Zonal Agricultural Research Station (ZARS), UAS, GKVK, Bengaluru, for extending field and laboratory facilities during the Kharif 2023 and 2024 seasons. We also thank the ICAR-AICRP on Small Millets for technical guidance and support throughout the study. The authors are grateful to all staff members who assisted during field experimentation and data collection.

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