Seasonal incidence of mustard aphid relation to abiotic factors

Introduction

Rapeseed-mustard (Brassica juncea) is a crucial oilseed crop cultivated in tropical and subtropical regions (Pandey et al., 2023) [12] . In India, it ranks as the second most important oilseed after soybeans, contributing approximately 20-22% to the total production (Singh et al., 2017) [22] . The seeds of rapeseed-mustard contain 35-45% oil and 20-24% protein (Gill et al., 2011) [7] . Similarly, Gobhi sarson (B. napus L.) is a high-yielding oilseed variety cultivated in regions like Punjab, Haryana, and Himachal Pradesh. It is recognized for its adaptability and the quality of its oil (Shekhawat et al., 2012) [17] . However, insect pests are a significant factor in reducing mustard yields, with more than 43 species impacting rapeseedmustard crops in India. The major pests are leaf miners (Phytomyza horticola), painted bugs (Bagrada hilaris), aphids (Lipaphis erysimi), and sawflies (Athalia lugens proxima). (Singh et al., 2000) [22] . Among these, the mustard aphid is particularly harmful, causing notable yield reductions. While mustard aphids remain active throughout the year, they are most prevalent from September to March, which coincides with the growth period of cruciferous crops. During less favorable times, they can feed on wild or cultivated crucifers found in moist environments, orchards, and home gardens (Sidhu & Singh, 1964) [19] . Lipaphis erysimi primarily reproduces through viviparous parthenogenesis, with males appearing only during cooler months (Kawada and Murai, 1979) [8] . With two in January, three in February, and three in March, the aphid completes an average of eight generations during this time. (Dwivedi et al., 2018) [6] . When mustard crops are out of season, these pests do not vanish but instead find refuge in other plants such as Ashwagandha (Withania somnifera), cauliflower (B. oleracea), cabbage (Brassica oleracea var. capitata), and radish (Raphanus sativus) between May and July. These alternative hosts allow the pests to survive, enabling them to reinfest mustard crops once they are replanted (Das, 2002) [4] . Aphids damage plants by feeding on the sap of young shoots, flowers, and tender pods, which weakens the plants and hinders their growth. They also secrete honeydew, which fosters the growth of black sooty mold on the leaves, blocking photosynthesis. This leads to yellowing, curling, and drying of the leaves. In severe cases, the plants develop fragile pods with few seeds, and the sooty mold further hampers the plant's ability to photosynthesize (Chaudhary and Pal, 2006; Sekhon, 1989) [22,15] . Mustard aphid (Lipaphis erysimi) represents a significant threat to rapeseed-mustard crops, leading to considerable yield and quality losses. It has the potential to cause up to 96% yield loss and a 5-6% reduction in oil content (Shylesha et al., 2006) [18] .

Under different agro-climatic conditions, yield losses can range from 35.4% to 73.3%, with some instances resulting in complete crop failure (Bakhetia, 1983; Ashutosh & Kunwar, 2024) [2,1] .

Materials and Methods

In the Rabi seasons of 2023-24, the current study was carried out at Lovely Professional University in Phagwara, Punjab. .The test crop, Gobhi Sarson (Brassica napus) variety GSC-07, was cultivated under field conditions. The crop was sown on November 6 th and grown in 100-squaremeter plots following standard agronomic practices. Throughout the study period, no insecticides were applied to the crop to allow for the natural progression of mustard aphid infestation. Lipaphis erysimi was recorded weekly from its initial appearance until its population declined . The observations were made under natural field conditions without any plant protection measures. Aphid counting performed on the top 10 cm of the terminal shoot (twig) using a camel hairbrush to dislodge the aphids onto a white paper sheet for accurate enumeration. To assess the influence of environmental factors on aphid population dynamics, key meteorological parameters were recorded daily for both cropping seasons. These included maximum and minimum temperatures, morning and evening relative humidity, rainfall, wind speed, evaporation, and the number of rainy days. Weather data were obtained from meteorological observatory at Lovely Professional University, Phagwara, Punjab, India. To study the correlation between the physical parameters with aphid population was worked out by bivariate coefficient of correlation in IBM SPSS 22.0 Software.

Results and Discussion

The data in Table 1 shows that aphid infestation began in the first standard week, starting on January 3 rd 2024. At first, the aphid population was quite low, with just (4.9 per 10 cm of the top twig). However, it gradually started to increase from the second standard week, reaching (12.40 per 10 cm top twig). Over the next few weeks, the aphid population continued to rise (47.50 per 10 cm top twig in the third standard week, 67.70 per 10 cm top twig in the fourth standard week, and 93.50 per 10 cm top twig in the fifth standard week). By the sixth and seventh standard weeks, the population reached higher numbers, with (125.30 and 146.30 aphids per 10 cm top twig, respectively). The highest population was recorded in the eighth standard week at (166.30 per 10 cm top twig). After that, the aphid population slowly started to decline, with (108.60 per 10 cm top twig in the ninth standard week, 88.40 per 10 cm top twig in the tenth standard week, 63.40 per 10 cm top twig in the eleventh standard week, and 41.60 per 10 cm top twig in the twelfth standard week). The lowest count was observed in the thirteenth standard week, with just (21.70 per 10 cm top twig). The correlation coefficients suggest a positive correlation with maximum temperature (r= 0.241), evaporation (r=0.228), No. of. Rainy days (r= 0.246).while Relative humidity Morning (r=-0.274) and Evening (r=-0.428) and rainfall (r=-0.087) showed negative effects, and a positive significant association with wind speed (r=0.602) at 0.05 level was noticed (Table 2). The present findings is in conformation with the results of Dotasara et al., (2022) [5] who revealed that population of Lipaphis erysimi arrived in 1 st Standard mean week of January during the period of 2017-18. An experiment conducted by Singh and Lal (2012) [20] conclude that mustard aphid population began to appear second week of January which may differ from the above research result due to certain climatic conditions and factors which can affect the growth and development of the pest. The findings was in conformation with Singh et al., (2018) [23] who revealed that peak population of mustard aphid found between 6 th and 8 th Standard mean week it also supports Kumar et al., (2024) [9] . The present study is in accordance with the observations of Dwivedi et al. (2018) [6] , who reported the disappearance of the aphid population by the fourth week of March in both study years. The above results are in conformity with the findings of Patel et al., (2019) [13] who reported windspeed showed significant positive correlation and tells that maximum temperature are positive but non-significant correlation. However, the presents findings were in accordance with results of Pradhan et al., (2020) [14] nonsignificant negative correlation was observed with evening relative humidity. The results are in conformity with Shaila et al., (2022) [16] Relative humidity morning is correlated negatively. Minimum temperature exhibited non-significant negative correlation in the present findings which is in accordance with the findings of Srija et al., (2024) [24] . The above results are similarly to Mishra and Mukherjee (2020) revealed that rainfall and No. of. rainy days was nonsignificant. Evaporation exhibited that non-significant positive correlation in the present findings which is accordance to the findings of Kumar et al., (2021) [10] .

Conclusion

Based on the findings, it can be concluded that the appearance of Lipaphis erysimi Kalt. began in the first standard week of 2024. The mustard aphid population peaked during the sixth and Eight standard weeks. The correlation analysis between various weather parameters and insect pest populations showed that aphids had a significant positive correlation with wind speed and a negative correlation with relative humidity (both morning and evening), minimum temperature, and rainfall. Aphids also showed a positive correlation with maximum temperature as well number of rainy days is non-significant was observed.

Acknowledgement

AcknowledgementsI would like to express my sincere gratitude to everyone who has supported and guided me throughout the course of this research. First and foremost, I extend my deepest thanks to Lovely Professional University, Phagwara, Punjab, for providing me with the necessary resources and an inspiring academic environment.

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