Seasonal incidence of mustard aphid (Lipaphis erysimi Kalt.) and its natural enemies in relation to weather parameters under different sowing conditions

Introduction

Evidence of the production of brassica crops dates back to about 5000 BC, making it one of the earliest crops ever cultivated. In the past, various Brassica plants were utilized as oil sources and condiments, and mustard still plays a significant role in Indian cuisine. As edible oilseeds, mustard and rapeseed are widely consumed and continue to play a significant role in the Indian agricultural economy (Prakash and Hinta, 1980) [18] . Among the seven main edible oilseed crops cultivated in India, rapeseed-mustard (Brassica spp.) makes up around 28.6% of the nation's total oilseed production, ranking second only to groundnuts, which account for 27.8% of the country's oilseed economy. The genus Brassica and family Brassicaceae include the oilseed Brassica crops. In India, these crops are frequently grown in the winter under both rainfed and irrigated circumstances. Although it may be cultivated well in both tropical and temperate climates, mustard is generally a coolseason crop. (Shekhawat and others, 2012) [20] . A significant source of edible oil with high concentrations of erucic and linolenic acids, mustard seeds have a high oil content (about 40%). The seeds' high fat, protein, carbohydrate, mineral, and fiber content makes them nutritious as well. Mustard seeds and oil are frequently used in pickles, curries, sauces, and vegetable preparations because of their strong flavor. Additionally, mustard oil has a number of industrial and medical uses, such as in the production of soap, lubricant, hair oils, and conventional remedies for a range of illnesses (Anonymous, 2023) [2] .

Seven distinct mustard and rapeseed species can be found in India: Brassica juncea and Brassica rapa (yellow sarson), Eruca sativa (Taramira), Brassica nigra, Brassica rapa var. toria, Brassica compestris, and Brassica tournefortii. It is a crop that requires less water to develop and can tolerate moderate salt. Its seed and oil are fragrant due to the presence of sinigrin and a high percentage of glucosinolate (Nagraj, 1995) [12] . Even though mustard aphid seasonal incidence has been extensively researched, knowledge of its population dynamics under various sowing dates and their relationship to natural enemies and meteorological factors is still crucial for accurate pest predictions and management. Aphid appearance, population growth and decline can all be impacted by variations in sowing time, which in turn can impact pest risk. Therefore, during the Rabi season 2025-2026, the current study was conducted to evaluate the impact of sowing dates on the seasonal incidence of Lipaphis erysimi (Kalt.) and its related natural enemies in relation to climatic parameters.

Materials and Methods

The field experiment was conducted during the Rabi season 2025-26 at the field of AICRP on Linseed and Mustard, Nagpur (Dr. PDKV, Akola), to study the influence of sowing date on the seasonal incidence of mustard aphid, Lipaphis erysimi (Kalt.) and its natural enemies in relation to weather parameters. Mustard variety TAM 108-1 was sown on 30 th October 2025 and 30 th November 2025 in separate 9 × 9 m plots with a spacing of 45 × 10 cm under non-replicated and pesticide-free conditions. Five plants were randomly selected and tagged in each plot and observations were recorded at weekly intervals. Aphid population was recorded on a 10-cm terminal central twig and expressed as aphid's/10 cm twig. Ladybird beetles were recorded as beetles/plant, while Diaeretiella rapae was recorded as Mummified aphids/10 cm twig. Weekly weather data, including rainfall, rainy days, maximum and minimum temperature, morning and evening relative humidity, bright sunshine hours, wind speed and evaporation, was obtained from the meteorological observatory at college of agriculture, Nagpur. The observations were analyzed according to Standard Meteorological Weeks (SMW) to determine population build-up, peak incidence and decline. Pearson's correlation coefficient (r) was used to determine the association of aphid population with natural enemies and weather parameters and significance was tested at the 5% probability level.

Results and Discussion

Seasonal incidence of mustard aphid and associated natural enemies on mustard under different sowing dates.

Based on weekly monitoring of mustard aphid, L. erysimi (kalt.) and associated natural enemies viz., lady bird beetles and parasitoid (D. rapae) in mustard field. The data clearly revealed variations in pest incidence as a function of the difference in date of sowing, most likely due to changing environmental conditions. [14] , Kulkarni and Patel (2001) [11] , and Gauraha et al. (2002) [7] , who reported peak aphid incidence during favourable winter conditions. The occurrence of ladybird beetles following aphid build-up also agrees with Kulkarni and Patel (2001) [11] , indicating a close association between aphid incidence and predator activity.  Incidence of Lady Bird Beetle: With a mean population of 0.4 beetles per plant, the predator ladybird beetle activity was initially observed during the 1 st SMW, which coincided with the sharp rise in aphid populations. As the aphid infestation peaked in the 4 th SMW, the predator population gradually increased and reached its maximum density of 3. April 2026. The aphid population showed a progressive increase, reaching its peak during the 6 th SMW on 11 th February 2026 and then gradual decline was evident. An initial population of 0.8 aphids per 10 cm apical twig was noted during the 1 st Standard Meteorological Week (SMW) on 7 th January 2026. After that, during the 2 nd , 3 rd , and 4 th SMWs, the aphid population progressively increased to 4.2, 16.8, and 41.2 aphids per 10 cm twig, respectively. From the 5 th SMW onward, the population of aphids increased rapidly, reaching 69.8 aphids per 10 cm twig. During the 6 th SMW (11 th February 2026), the population peaked at 88.4 aphids per 10 cm apical twig. Following the peak, the aphid population declined steadily to 51.8, 27.8, 14.6, 2.4, 1.2, 0.7 and 0.2 aphids per 10 cm twig during the 7 th to 13 th SMWs, respectively. The decline in aphid abundance coincided with increasing maximum temperature, decreasing relative humidity and advancement of crop maturity. The results of Panda et al. (2000) [14] and Gauraha et al. (2002) [7] , who observed peak aphid incidence during favourable winter conditions, were similar to the mustard aphid occurrence during the late-sown crop.

Seasonal incidence of mustard aphid (Lipaphis erysimi) and associated natural enemies (lady bird beetle and parasitoid of mustard aphid,

The current finding of a negative correlation between the population of L. erysimi (Kalt.) and temperature confirms the findings of Dogra et al. (2001) [6] , which suggest that aphid multiplication is favoured by lower temperatures. correlated with maximum temperature (r = -0.072), minimum temperature (r = -0.085), rainfall, and rainy days (r = -0.023 for both), according to correlation analysis. On the other hand, there were positive associations between morning and evening relative humidity (r = 0.568 and 0.430, respectively). Wind speed indicated a positive correlation (r = 0.291), whereas bright sunshine hours revealed a negative association (r = -0.251). Morning relative humidity had the largest positive correlation with the D. rapae population, whereas evaporation had the strongest negative correlation (r = -0.597).  Correlation of Mustard Aphid with Predator, Lady Bird Beetle: The population of mustard aphids increased rapidly from 0.8 aphid's/10 cm twig in the 1 st SMW to 88.4 aphid's/10 cm twig in the 6 th SMW, which also happened to be the largest number of lady bird beetles (3.0 beetles/plant). Increased aphid availability favoured the abundance of predatory lady bird beetles, as seen by the strong positive and significant connection (r = 0.981) between mustard aphid and lady bird beetle populations at the 5% level of significance.  Correlation of Mustard Aphid with Parasitoid, Diaeretiella rapae (Mummified aphid): The parasitoid D. rapae population's abundance increased in along with the mustard aphid population, according to a simple linear association. It reached a maximum of 3.6 Mummified aphids /10 cm twig during the 6 th SMW, when the aphid population similarly peaked at 88.4 aphid's/10 cm twig. mustard aphid populations showed a strong positive and significant connection (r = 0.959) at the 5% level of significance, suggesting that higher aphid availability favoured parasitoid incidence.

 Incidence of Lady

Conclusion

In contrast to the crop seeded on November 30 th , 2025, which reported a relatively lower peak of 88.4 aphid's/10 cm twig during the 6 th SMW, the crop sown on October 30 th , 2025, recorded the greatest aphid population, reaching 130.0 aphids/10 cm twig during the 4 th SMW. Delaying sowing hence caused a shift in the peak incidence period and relatively decreased aphid abundance. A close densitydependent interaction between the pest and its natural enemies is shown by the fact that the populations of ladybird beetles and Diaeretiella rapae grew and peaked at the same time as the aphid population. While other climatic indicators indicated non-significant correlations, the minimum temperature under October 30 th cultivation revealed a large negative and significant correlation with aphid population. Aphid population was positively and significantly correlated with morning relative humidity under (November 30 th ) late-sown conditions, whereas the other weather parameters exhibited nonsignificant associations. Under both sowing dates, the aphid population showed a substantial and positive correlation with D. rapae and ladybird beetles, suggesting that the abundance of natural enemies rose as the aphid population increased. Overall, the study showed that the timing and intensity of mustard aphid incidence as well as the natural enemies that are linked to it, were influenced by the sowing date.

Acknowledgement

AcknowledgementsI express my sincere gratitude to the College of Agriculture, Nagpur, for providing the necessary facilities and support to conduct the present investigation. I am deeply thankful to my Advisor, Dr. V. J. Tambe, for his valuable guidance, continuous encouragement, constructive suggestions and supervision throughout this research work. I am also grateful to the members of my Advisory Committee and the International Journal of Agriculture and Food Science https://www.agriculturaljournals.com Department of Entomology, College of Agriculture, Nagpur, for their valuable suggestions, technical guidance and assistance during the course of this research work.

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