Effect of sowing windows on larval population dynamics of Helicoverpa armigera in chickpea under protected and unprotected conditions

Introduction

Chickpea (Cicer arietinum L.) is an important pulse crop cultivated worldwide and serves as a major source of dietary protein, particularly in India. However, its productivity is severely constrained by insect pests, among which the gram pod borer, Helicoverpa armigera (Hubner) (Lepidoptera: Noctuidae), is the most destructive. The pest is highly polyphagous, feeding on more than 180 host plant species, and causes severe damage by feeding on flowers and developing pods, resulting in yield losses ranging from 30-40%, which may exceed 80% under favourable conditions (Fitt, 1989; Sehgal and Ujagir, 1990; War et al., 2024) [3,7,9] . The population buildup of H. armigera is largely influenced by crop phenology and prevailing weather conditions, making sowing time a crucial cultural practice for minimizing infestation (Shah and Shahzad, 2005; Meena and Bhatia, 2014) [8,5] . Therefore, the present study was conducted to evaluate the influence of different sowing windows, varieties, and protection regimes on the seasonal dynamics of the larval population of H. armigera in chickpea under field conditions.

Materials and Methods

Experimental site

Experimental details

The experiment was conducted in a split-split-plot design with three replications and sixteen treatment combinations considering different protection, varieties, and sowing windows.

Number of larvae per meter row length (mrl -1 )

The larval population of pod borer was recorded at a weekly interval on one meter row length at three spots selected randomly in each plot from the first appearance till harvesting of the crop in the early morning hours without disturbing the flora and fauna. (Protection -Flubendiamide 480 SC (39.35% w/w) @ 0.4 ml/L will be applied at the ETL level)

Results and Discussion

Number of larvae per meter row length (mrl -1 )

The data on larval population per meter row length (mrl⁻ 1 ), as influenced by various treatments, are presented in Table 1 and graphically illustrated in Figure 2 for the cropping seasons of 2023 and 2024. A progressive rise in larval count (mrl⁻ 1 ) was observed from 28 DAS (0.44 and 0.30) to a maximum at 63 DAS (2.05 and 2.09), followed by a subsequent decline towards harvest (0.21 and 0.25) during 2023 and 2024, respectively.

Effect of protection treatments

The results revealed that protection treatments exerted a significant influence on larval population during most of the crop growth stages in both 2023 and 2024 (Table 1). The mean number of larvae per meter row length (mrl -1 ) increased with the advancement of chickpea age. Statistically, the highest mean number of larvae per meter row length (mrl -1 ) registered under unprotected conditions was 2.98 and 3.25, whereas under protected conditions (Flubendiamide 480 SC @ 0.4ml/L) it was 1.12 and 0.94 at 63 DAS during the years 2023 and 2024, respectively. During the early stages (28 to 42 DAS), the mean number of larvae per meter row length (mrl -1 ) remained statistically at par between protected (P 1 ) and unprotected (P 2 ) plots, indicating minimal infestation in the vegetative phase. A pronounced peak in larval population was recorded around 70 DAS, with the mean number of larvae reaching 2.35 mrl -1 in unprotected plots as against only 0.52 mrl -1 in protected plots. Thereafter, a sharp decline was observed towards harvest, with the lowest infestation recorded at 90 DAS (0.34 and 0.12 larvae mrl -1 in unprotected and protected plots, respectively). The lower larval incidence under protected conditions (Flubendiamide 480 SC @ 0.4ml/L) can be attributed to its mode of action as a selective phthalic acid diamide insecticide, which targets ryanodine receptors in insect muscles, causing uncontrolled calcium (Ca 2+ ) release leading to paralysis and death of larvae. These findings are in agreement with the observations of Dinesh et al. (2017) [2] , who reported that Flubendiamidetreated plots recorded minimal H. armigera infestation and superior pod protection in chickpea compared to untreated controls.

Effect of varieties

The mean number of larvae per meter row length (mrl -1 ) influenced by varieties was significant at flowering and pod initiation stages of crop growth during the years 2023 and 2024 (Table 54). There was no major fluctuation in the number of larvae per meter row length (mrl -1 ) among both the varieties. Across all growth stages, variety Phule Vikram (V 1 ) recorded the lowest number of larvae per meter row length (mrl -1 ) (0.19 and 0.25) as compared to variety Vijay (V 2 ) (0.23 and 0.25) at harvest during both years. Thus, the period of increase in the number of larval populations was observed between 28 and 63 DAS, after which a gradual decline occurred towards harvest. (Choudhary et al. 2024) [1] . This trend may be due to inherent genetic potential rather than the effect of external weather parameters, which prevailed more or less in a similar range along the growing period of varieties.

Effect of sowing windows

The data presented in Table 1 revealed that the larval population of H. armigera was influenced by different sowing windows across the years 2023 and 2024. During the initial stages (28 to 42 DAS), the mean larval population remained low and statistically at par across all sowing windows, indicating minimal pest incidence in the early vegetative phase. This observation is consistent with previous studies, where early larval appearance was recorded only after several weeks of post-sowing (Meena and Bhatia, 2014; Choudhary et al., 2024) [5,1] . With crop advancement, a gradual increase in larval population was observed between 49 and 63 DAS. Among the sowing windows, S 3 (45 MW) recorded the highest mean larval population (2.25, 2.77 and 2.66 larvae/m row in 2023 at 49, 56 and 63 DAS, respectively), whereas S 1 (41 MW) consistently showed the lowest infestation during these stages. This pattern indicates that mid to late sowing windows (S 3 ) coincide with more favourable climatic conditions for pest multiplication, such as rising temperatures and relative humidity during the flowering to pod formation stages, in agreement with the findings of Pavani et al. (2019) [6] and Shah and Shahzad (2005) [8] . During the later stages of crop growth (70 to 90 DAS), a declining trend in larval population was recorded across all sowing windows, reflecting the natural decline of pest incidence towards crop maturity. The early sown crop (S 1 ) exhibited the lowest larval population at 90 DAS (0.12 larvae/m row), whereas the highest infestation was noted in S 3 (0.37 larvae/m row), indicating that late sowings may escape peak pest incidence to some extent but are prone to higher larval buildup during critical reproductive stages. These findings align with observations from rabi seasons 2022-23 and 2023-24, where peak Helicoverpa populations were recorded during February (7 -8 MW), following initial appearance in December (49 -50 MW) (Choudhary et al. 2024) [1] .

The variation in pest incidence among sowing windows may be attributed to the synchronization of larval activity with crop phenology and prevailing weather conditions, including temperature, relative humidity and rainfall (Kumawat et al. 2025) [4] . Early sowings (S 1 and S 2 ) coincided with relatively lower temperatures during vegetative growth, which suppressed early pest multiplication, whereas mid to late sowings (S 3 and S 4 ) experienced warmer temperatures and longer sunshine hours, favouring increased pest activity and population buildup.

Effect of interaction

Analysis of the number of larvae/m row length for both years revealed significant two-way interactions between protection and varieties (Table 2), protection and sowing windows (Table 3) and varieties and sowing windows (Table 4), as well as a significant three-way interaction among protection, varieties and sowing windows (Table 5). Among the treatment combinations, P 2 V 1 and P 2 V 2 consistently recorded higher larval count during 42 to 77 DAS in 2023, 2024 and the pooled mean. Similarly, P 2 S 3 , V 1 S 3 and V 2 S 3 in 2023, 2024 and the pooled mean consistently recorded higher larval count. Notably, the combined effect of protection, variety and sowing windows (P 2 V 1 S 3 and P 2 V 2 S 3 ) was superior to all other interactions across 42 to 77 DAS in both years and the pooled mean.

Conclusion

The seasonal population dynamics of Helicoverpa armigera indicated that larval incidence increased progressively from 28 DAS, reached its peak between 49 and 63 DAS, and declined thereafter towards crop maturity. Early sowing (41 MW) consistently recorded the lowest larval population, whereas delayed sowing (45 MW) favoured higher infestation. Protected plots treated with Flubendiamide 480 SC (0.4 ml L⁻¹) significantly suppressed larval population compared to unprotected plots, while the variety Phule Vikram exhibited slightly lower larval incidence than Vijay. The findings suggest that early sowing combined with timely crop protection can effectively reduce H. armigera infestation and should be considered as an important component of integrated pest management in chickpea.

References

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