Population dynamics of mung bean insect pests correlating to weather parameters

Introduction

After pigeon pea and chickpea, greengram (Vigna radiata), sometimes referred to as mungbean or moong, is the third most important pulse crop. Belonging to the Leguminosae or Fabaceae family, it's crucial pulse crop in India, contributing to 54% of global production and 65% of total acreage (Singh and Singh, 2014) [13] . Renowned for its nutritional value, mungbean plays a vital role in human nutrition and enhances soil fertility through N fixation. Originating in India, it is cultivated primarily in East of Asia and is valued for its seed's desirability, nutritional content, easy digestibility, and non-flatulent nature. Mungbean stands out because of its wide geographical distribution, minimal water requirements, and its It is an important pulse crop in India, accounting for 54% of worldwide output and 65% of total acreage. It belongs to Leguminosae or Fabaceae family (Singh and Singh, 2014) [13] . It is recognized for its great nutritional value of mungbean is essential to human nutrition and improves soil fertility by fixing nitrogen. It comes from India and is grown mostly in East Asia. It is prized for the nutritious value, easy digestion, and non-flatulent character of its seeds. Mungbean is unique because to its extensive geographic range, low water needs, and application as green gram manure for soil enrichment via nitrogen fixation (Tamang et al., 2017) [14] . Application as green gram manure for soil improvement via nitrogen fixation (Tamang et al., 2017) [14] . Even though India leads the world in greengram production, its output has increased to about 40.38 lakh hectares, or 11% of the overall pulse production in 2021-2022. Insect pests poses a significant threat to mungbean, with aphids, leafhoppers, whiteflies, thrips, pod borers, and spotted pod borers being major concerns Islam et al., 2008 [3] . The impact of these pests is influenced by meteorological factors such as the degree of humidity, temperature, and precipitation. The pod borer, M. vitrata, poses a particular threat during the reproductive stages of green gram, leading to lower yields. Spotted pod borer outbreaks are a common occurrence, contributing to reduced yields. Mungbean is greatly impacted by sucking insect pests, such as thrips, jassids, aphids, and leafhoppers (Dietz, 1914) [2] .

Notably, yield decreases of up to 70% have been reported as a result of whitefly harm. This research intends to explore the population dynamics of important insect pests in mungbean (greengram) in connection to meteorological conditions, given the significance of these pests and their influence on mungbean output. The study tackles the urgent need to comprehend how insect pests and weather interact effectively manage pests in the production of mungbean (greengram).

Methodology

The study conducted at the Agricultural Research Station in Badnapur during the 2021-22 kharif season. Tillage operations performed to enhance soil health. Mung bean, a leguminous crop, received half the nitrogen and full P2O5 before sowing. Recommended agronomic practices followed, including thinning, gap filling, irrigation, hand weeding, and hoeing. The greengram crop (BM2013-2 variety) sown in early July 2022, with a plot size of 10 x 10 m and 30 cm row-to-row and 10 cm plant-to-plant spacing. Weekly observations of whiteflies, aphids, thrips, and leafhoppers-sucking pests-from the top, middle, and bottom trifoliate leaves of 10 randomly chosen plants were made. Information displayed as the average frequency of sucking insects on each trifoliate leaf. This data and meteorological characteristics have been linked by statistical analysis. Pod borers (Maruca vitrata and Helicoverpa armigera) were observed in populations from the time of their emergence till the harvesting of crops. Weekly counts of larval populations on 10 randomly chosen tagged plants are conducted. Ten randomly chosen tagged plants were used to measure the incidence by calculating the mean pod damage and total number of damaged pods.

Results & Discussion Aphids (Aphis craccivora)

First discovered in the 31 st SMW, aphids (Aphis craccivora) ranged in population size from 5.1 to 9.2 aphids/trifoliate leaf (Table1). From the 31 st to the 33 rd SMW, the population grew progressively, reaching a high of 9.2 aphids/trifoliate leaf in the 33 rd SMW. The findings were consistent with the findings of Kumar et al. (2022) [4] , who reported that Aphis craccivora was first observed on the crop in the 32nd SMW with an average of 1.20 aphids per plant. The presence of A. craccivora continued until the 38th SMW, with the peak population reaching 8.70 aphids per plant during the 36th SMW. Table 2 showcases the association between environmental conditions and aphid activity. While there was a positive correlation between maximum temperature (r=0.478) and evening relative humidity (r=0.512) with aphid population, the effects were not deemed statistically significant. On the other hand, morning relative humidity (r=-0.420), rainfall (r=-0.231), and minimum temperature (r=-0.201) all had a negative impact on aphid population, but these relationships were also found to be nonsignificant. According to the results of Prince Mahore (2023) [7] , there is evidence that the minimum temperatures in the morning and evening, wind speed, rainfall, and relative humidity do not significantly affect aphid population levels. Additionally, their study found a non-significant positive relationship between daylight hours and aphid population. This conclusion is in line with the findings of Bairwa and Singh (2017) [1] , who also reported a lack of significant correlation between morning and evening minimum temperatures, wind speed, rainfall, and relative humidity, and aphid population. Furthermore, their study also revealed a non-significant positive correlation between daylight hours and aphid population.

Whitefly (Bemisia tabaci)

Whitefly damage, ranging from 1.6 to 2.1, occurred from the 31 st to the 36 th SMW. The 36 th SMW had the lowermost occurrence (1.4 whiteflies/trifoliate leaves), whereas the 33 rd SMW had the greatest incidence (2.1 whiteflies/trifoliate leaves). After that, the incidence of whiteflies steadily dropped from the 34 th to the 36 th SMW till harvesting, with the last observation showing 1.41 whitefly/trifoliate leaves. Present investigation was similar with Nitharwal and Kumawat (2009) [9] , who noted that whiteflies began to arrive in the 35 th week of the meteorological calendar and peaked in the 39 th . The whitefly population began to increase in the first week of August (32 SMW), according to Singh et al. (2019) [12] . It peaked in the beginning week of September (36 SMW) with 14.20 whiteflies per three leaves. The highest temperature and the number of whiteflies have a non-significant positive connection (r=0.061) according to Table 2. The whitefly population was positively impacted by the lowest temperature and night time relative humidity (r=0.355 and r=0.07, respectively), this effect was not statistically significant. There were non-significant negative relationships found with morning relative humidity (r=-0.575) and rainfall (r=-0.040). These results show a substantial negative relationship with rainfall and a significant positive association with the number of whiteflies, which is in line with Prince Mahore's (2021) [7] findings the. Whitefly and highest temperature were also found a positive significant correlation by Bairwa and Singh (2017) [1] , while rainfall and relative humidity (maximum and minimum) were found to have non-significant negative correlations. Other factors, on the other hand, showed positive non-significant relationships with abiotic factors. [4] findings of Thrips tabaci appearing on the crop in the 32 nd SMW (2.10 thrips/plant) and infesting until the 38 th SMW, with a peak population of 7.00 thrips/plant in the 35 th SMW. Table 2 displays the relationship between thrips and meteorological parameters, indicating a moderate effect. Maximum temperature (r=0.253), minimum temperature (r=0.014), and relative humidity at morning (r=0.103) positively influenced thrips population but were non-significant. Rainfall had a non-significant negative correlation (r=-0.086) with thrips population, like Sarkar et al. (2019) [11] findings that thrips were unaffected by rainfall.

Pod borer (Helicoverpa armigera)

Helicoverpa armigera occurrence followed a similar pattern, initially seen around the 32 nd SMW and ranging from 0.7 to 1.4 larvae/plant. From the 32nd to the 35th SMW, the population grew; in the 36th SMW, it peaked at 8.50 larvae/ten plants. Pal et al. (2021) [10] findings supported this, with H. armigera appearing in the 31 st SMW (0.50 larvae/ten plants) and reaching a peak of 8.50 larvae/ten plants in the 36 th SMW. Table 2 presents the association between H. armigera and weather parameters, showing little impact. Highest temperature (r=-0.173), rainfall (r=-0.112), and evening R. humidity (r=-0.209) had non-significant negative correlation with H. armigera populations. Minimum temperature (r=0.239) found a positive non-significant correlation. As stated by Pal et al. (2021) [10] , who also found no statistically significant associations with minimum temperature, relative humidity, and rainfall, morning relative humidity (r=-0.820) associated strongly and adversely with the H. armigera population. The maximum temperature and gram pod borer infection were shown to be significantly inversely correlated.

Maruca vitrata (Spotted pod borer)

The initial Maruca vitrata population showed up during the 32 nd SMW, ranging from 0.6 to 1.3 larvae/plant. The population gradually increased from the 32nd to the 36 th SMW, peaking at 1.3 larvae/plant in the 35 th SMW. Kumar et al. (2022) [4] findings supported this, with M. vitrata appearing on the crop in the 34 th SMW (0.90 larvae/plant) and infesting until the 38 th SMW, reaching a peak of 2.30 larvae/plant in the 36 th SMW. Pal et al. (2021) [10] reported the spotted pod borer M. testulalis appearing in the 31 st SMW (0.66 larvae/ten plants) and reaching a peak of 9.66 larvae/ten plants in the 36 th SMW. Table 2 illustrates the correlation coefficients between M. vitrata and weather parameters. There were non-significant negative correlations (r=-0.371, r=-0.478, and r=-0.380) between the highest temperature, relative humidity in the morning and evening, and rainfall, however there were significant positive correlations (r=0.612 and r=0.120) between rainfall and minimum temperature. Umbarkar et al. (2010) [15] supported these findings, noting non-significant negative effects of relative humidity (maximum and minimum) and rainfall, with positive nonsignificant impacts of temperature (maximum and minimum), wind speed, sunshine hours, and evaporation on M. vitrata population fluctuation.

Leafhopper (Empoasca kerri)

Leafhopper incidence began in the 31 st SMW at 1.2 leafhoppers/trifoliate leaf, persisting until the 36 th SMW. The range observed was 1.2 to 1.7 leafhoppers/trifoliate leaf, with the peak population (1.7 leafhoppers/trifoliate leaf) occurring in the 33 rd SMW. Kumar et al. (2022) [4] reported similar results, with Empoasca kerri appearing on the crop in the 32 nd SMW (3.50 jassids/plant) and infesting until the 38 th SMW, reaching a peak population of 7.50 jassids/plant in the 35 th SMW. Mohapatra et al. (2018) [8] noted E. kerri as an significant pest of black gram, appearing in the 35 th SMW and reaching a peak population of 36.80 jassids/cage in the 39th SMW. In Table 2 observed that correlations between leafhoppers and weather parameters. There was a non-significant negative relationship (r=-0.127) with rainfall, and non-significant positive relationships (r=0.121, r=0.201, and evening relative humidity, r=0.166) with the leafhopper population. Similarly Mohapatra et al. (2018) [8] , who reported non-significant positive correlations between the leafhopper population and the maximum temperature, minimum temperature, and rainfall, showed a nonsignificant negative correlation with relative humidity. Bairwa and Singh (2017) [1] also reported a non-significant positive correlation between maximum temperature, and a positive but non-significant correlation between the minimum temperature and the population of jassids.

Green semilooper (Chrysodeixis acuta)

The green semilooper first showed up on the crop in the 31 st SMW at 2.6 semiloopers/trifoliate leaf. It continued to show up in the crop until the 36 th SMW, when its numbers varied from 1.2 to 1.7 semiloopers/trifoliate leaf. The maximum population (1.3 semiloopers/trifoliate leaf) was observed on the 33 rd SMW. Kurly and Singh (2021) [6] reported similar findings, with the pest first observed in the 29 th SMW at 1.05 larvae/10 plants in 2016 and 1.28 larvae/10 plants in 2017. The highest population was noticed on the 33 rd SMW in 2016 (3.90 larvae/10 plants) and on the 32 nd SMW in 2017 (4.26 larvae/10 plants). Table 2 illustrates the correlation coefficients between semilooper and weather parameters. Semilooper actions were impacted by all factors. Maximum temperature (r=0.277) and evening relative humidity (r=0.271) showed non-significant positive correlations, whereas minimum temperature (r=-0.005) and morning relative humidity (r=-0.654) showed non-significant negative correlations. It was a noteworthy inverse relationship (r=-0.654) seen between semilooper populations and morning relative humidity. Kurly and Singh (2021) [6] discovered a positive and substantial link between green semilooper and meteorological factors. Specifically, they recorded strong correlations with maximum temperature (0.454**) and minimum relative humidity (0.495**).

Conclusion

In conclusion, the study on the cyclic occurrence of pests in kharif mung bean during the 2022 season revealed the presence of whiteflies, aphids, thrips, leafhoppers and two borers, H. armigera and M. vitrata, and the defoliator green semilooper. The peak populations of whiteflies, aphids, and leafhoppers were observed in the 33 rd (SMW). Thrips exhibited a significant negative correlation with relative humidity at morning (Rhm), while leaf hoppers showed a significant negative association with morning humidity. Morning relative humidity and H. armigera showed a negative, non-significant connection. There was a substantial positive association between the minimum temperature and the spotted pod borer. The green semilooper and Rh had a substantial inverse relationship in the morning.

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