Seasonal Incidence of Pod Borer Complex- Spotted Pod Borer, Maruca Vitrata (Geyer) and Pea Blue Butterfly, Lampides Boeticus (Linnaeus) in Black Gram In Relation To Weather Parameters

Black gram (Vigna mungo L. Hepper) is one of the most significant pulse crops in India and a short-season crop. In India, it is commonly referred to as urd bean or mash (Leguminaceae). It has a high protein content between 20.8 and 30.5 percent and total carbs between 56.5 and 63.7 percent (Kundagar et al., 2021). Black gram production in India is limited by a variety of factors, in which insect infestations being a key contributor (Singh and Kumar, 2016). Black and green gram yield losses in India were caused by insect infestations and varied from 7 to 35% (Selvam, 2018).Pulses in India have been affected by more than 250 insect infestations. Black gram production is significantly reduced by roughly twelve insect species, which are pests (Soundararajan and Chitra, 2012). Pod borer complex include Helicoverpa armigera (Hubner), Maruca vitrata (Geyer), M. testulalis (Geyer), Etiella zinckenella (Treitschke), Apion ampulum (Faust) and Lampides boeticus (Linnaeus). Among the pod borers, M. vitrata is a major constraint for the production of black gram at critical stages such as flowering and pod formation (Selvam, 2018). So, the present investigation was carried out to know the seasonal incidence of borers on black gram in two seasons and their relationship with meteorological parameters.

 The population dynamics of borers on black gram in relation to abiotic factors were studied by conducting two field experiments viz., field experiment I at Kunnathur, Tirupur, Tamil Nadu during Kharif 2020 and field experiment II at the Eastern farm of Pandit Jawaharlal Nehru College of Agriculture and Research Institute (PAJANCOA and RI), Karaikal, U. T. of Puducherry during Rabi 2020 – 2021. VBN (Bg) 8 black gram variety seeds were sown in both seasons with 30 x 10 cm spacing, and the crop was raised successfully by adopting recommended agronomic practices as per the crop production guide 2020 of Tamil Nadu Agricultural University. For seasonal incidence, insect pests were recorded at weekly intervals in ten randomly selected plants and at five different locations from germination to harvest. Larvae of borers were assessed by counting the number of larvae per plant randomly.selected plants per plot (Selvam, 2018). In order to find out the specific impact of meteorological parameters on borers, the data on larval population recorded in the experimental plot were correlated with maximum and minimum temperature, maximum and minimum RH, and rainfall during Kharif 2020 and Rabi 2020 – 2021. Weather data were obtained from the meteorological observatory of PAJANCOA and RI, Karaikal, U.T. of Puducherry.

Seasonal incidence of the black gram spotted pod borer, M. vitrata

The larval incidence of the spotted pod borer, M. vitrata appeared first at 42^nd SW (October) (14 larvae/ 50 plants) and had its highest peak at 45^th SW (November) (52 larvae/ 50 plants) during Kharif 2020 (Table 1) (Fig. 1). During Rabi 2020 – 2021, the pest appeared from 13^th SW onwards (April) (12 larvae/ 50 plants) and reached its highest peak at 16^th SW (April) (42 larvae/ 50 plants) (Table 2) (Fig. 2).  In both the season larval population declined at crop harvest with 8 larvae/ 50 plants at 48^th SW (November) during Kharif 2020 and 19 larvae/ 50 plants at 18^th SW (May) during Rabi 2020 – 2021.Shejulpatil et al. (2020) reported that there were peaks of M. vitrata in Pigeon pea at 43^rd SW (4^th week of October) and 45^th SW (1^st week of November) and reached its lowest population at 52^nd SW (last week of December) in Kharif 2017. Devi et al. (2019) reported that the incidence of M. vitrata on Pigeonpea was first noticed at 40^th SW (1^st week of October) and reached its peak level (6 larvae per plant) at 44^th SW (1^st of November) which coincided with the peak flowering stage of the crop, thereafter its incidence showed in decreasing trend during Kharif 2013. Biswas and Banerjee (2019) observed that spotted pod borer (M. testulalis) on black gram had been recorded maximum population in 7 WAS and 8 WAS during summer and Kharif 2016 and reached its peak in 10 WAS in both the seasons. Kundu et al. (2021) reported that the incidence of M. vitrata on black gram noticed at 13^th SW (3^rd week of March) and it reached its highest larval population at 19^th SW (2^nd week of May) and the damage continued till harvest in 2018 and 2019. These reports are in agreement with the present findings of Kharif 2020 and Rabi 2020 – 2021 seasonal incidence.

Seasonal incidence of the pea blue butterfly, L. boeticus

The larval incidence of the pea blue butterfly, L. boeticus appeared first at 42^nd SW (October) (22 larvae/ 50 plants) with the highest peak at 44^th SW (October) (52 larvae/ 50 plants) during Kharif 2020 (Table 1) (Fig. 1). During Rabi 2020 – 2021, larval incidence started from the 13^th SW (April) (15 larvae/ 50 plants) and reached its highest peak at 16^th SW (April) (46 larvae/ 50 plants) (Table 2) (Fig. 2). In both the season, larval population declined at crop harvest with 7 larvae/ 50 plants (48^th SW) (November) during Kharif 2020 and 17 larvae/ 50 plants (18^th SW) (May) during Rabi 2020 – 2021.Yadav et al. (2020) reported the appearance of blue butterfly (L. boeticus) on black gram at flowering and podding stage and it continued till the maturity of the crop. Rathore et al. (2017) reported that the larval incidence of L. boeticus on pigeonpea began with 0.75 larvae per 5 plants at 39^th SW (end of September), and reached the highest peak of 2.25 larvae per 5 plants at 42^nd SW (mid-October) during Kharif 2014. Bhadani and Patel (2019) reported L. boeticus in pigeon pea reached to the highest peak (4.3 larvae/ plant) at 43^rd SW (5^th week of October) during Kharif 2017 - 18 and 2018 - 19. Manisha et al. (2018) reported that larval activity of L. boeticus first appeared at 7^th SW (3^rd week of February) and major activity period was between March and April, and highest peak was recorded 1.55 larvae/ plant at 12^th SW (4^th week of March) in 2015. The above results are in agreement with the present findings of Kharif 2020 and Rabi 2020 – 2021 seasonal incidence.

Influence of meteorological parameters on the incidence of the spotted pod borer, M. vitrata

The correlation study showed that a significant positive correlation was observed between M. vitrata and maximum temperature (0.79). Non-significant positive correlation was recorded with minimum temperature (0.24) and rainfall (0.17), and non-significant negative correlation was recorded with maximum (-0.09) and minimum RH (-0.12) during Kharif 2020 (Table 3).During Rabi 2020 – 2021, a significant positive correlation was observed between M. vitrata and maximum (0.68) and minimum temperature (0.65) and non-significant with minimum RH (0.04) and rainfall (0.36). Significant negative correlation was recorded with maximum RH (-0.62) (Table 3). The multiple linear regression analysis showed that all the weather parameter together was responsible for significant variation of 82 and 79 per cent on larval incidence of M. vitrata (Table 3) during Kharif 2020 and Rabi 2020 – 2021, respectively.Rathore et al. (2017) studied the incidence of spotted pod borer (M. testulalis) in pigeonpea with weather parameters and exhibited that the pest population had positive non-significant with temperature, while non-significant negatively correlated with RH during Kharif 2014. Sravani et al. (2015) stated that maximum and minimum temperature and morning RH showed positive influence with M. vitrata larval population, where as rainfall and evening RH exhibited negative influence. However, none of them were significant except maximum temperature in green gram in Rabi 2014 – 2015. Kundu et al. (2021) also expressed that the incidence of M. vitrata on black gram exhibited a strong positive association with maximum and minimum temperature, morning and evening RH, and rainfall. These findings corroborate the present findings of the Kharif 2020 and Rabi 2020 – 2021 seasons.

Influence of meteorological parameters on the incidence of the pea blue butterfly, L. boeticus

 It was found that a significant positive correlation was observed between L. boeticus and maximum temperature (0.74) and non-significant with maximum (0.16) and minimum RH (0.13) and rainfall (0.33). Non-significant negative correlation was recorded with minimum temperature (-0.15) during Kharif 2020 (Table 3). During Rabi 2020 – 2021, significant positive correlation was observed with maximum (0.70) and minimum temperature (0.71), and non-significant with minimum RH (0.17) and rainfall (0.43). Non-significant negative correlation was recorded with maximum RH (-0.59) (Table 3). The multiple linear regression analysis showed that all the weather parameter together was responsible for significant variation of 77 and 80 per cent on larval incidence of L. boeticus (Table 3) during Kharif 2020 and Rabi 2020 – 2021, respectively. Biswas and Banerjee (2019) reported that blue butterfly population was significant negatively associated with maximum and minimum temperature and significant positively correlated with rainfall in green gram in summer and Kharif 2016 in West Bengal. Manisha et al. (2018) reported that the incidence of blue butterfly had non-significant positive correlation with maximum and minimum temperature, rainfall and evening RH and non-significant negative correlation with morning RH during 2015 – 2016. These findings are in agreement with the present findings of Kharif 2020 and Rabi 2020 – 2021 seasons.

Table 1. Seasonal incidence of borers on black gram during Kharif 2020

Table 2. Seasonal incidence of borers on black gram during Rabi 2020 – 2021

Table 3. Correlation and multiple linear regression between meteorological parameters and the population of borers in black gram during Kharif 2020 and Rabi 2020 – 2021

* Significance at 5 per cent level 

X₁-Maximum temperature (⁰C) X₂-Minimum temperature (⁰C) X₃- Maximum RH (%) X₄- Minimum RH (%) X₅-Rainfall (mm)

Fig. 1. Seasonal incidence of borers in black gram during Kharif 2020 and its relation with meteorological parameters

The seasonal incidence of M. vitrata and L. boeticus on black gram varied between Kharif 2020 and Rabi 2020–2021, with peak infestations occurring during the flowering and pod formation stages. Correlation analysis revealed that maximum and minimum temperatures significantly influenced the population dynamics of both species, whereas relative humidity and rainfall had mixed effects. The study underscores the role of weather parameters in pest outbreaks and emphasizes the need for climate-based pest management strategies to minimize yield losses in black gram cultivation.