Insect Pests of Black Gram (Vigna mungo L.) and Their Management in Vindhya Region

A field experiment was carried out at Entomology Instructional Farm, JNKVV, College of Agriculture, Rewa, (M.P.), during Kharif 2016-17. Popular black gram variety T-9, was sown in 200 sq. meter area followed the standard package and practices of the crop. The observations on the population of white fly and aphid was recorded at a weekly interval, starting from germination till harvesting of the crop. The number of pests was counted at three locations. At each location five plants were selected at randomly and tagged for observation. Populations of each insect were recorded on top, middle and lower leaves of tagged plants. The qualitative composition of insect pests and their natural enemies were carried out in the trial, laid out for population dynamics study. The incidence of the various pests of black gram and presence of natural enemies therein were recorded at weekly interval in one square meter area from three locations of the experimental plot. Therewith, the experiment was laid out in randomized block design with nine treatments including control having three replications. First spraying was done at 40 DAG and second spraying was done 15 days after 1^st spray. Population of white fly and aphid were counted one day before and one, 3,7,10 and 15 days after the insecticide application. The population of the pests were counted on top, middle and lower leaves of five randomly selected plants in each plot.

The data related to the population dynamics of white fly Bemisia tabaci, (Gennadius) and aphid, Aphis craccivora (Koch) in black gram under the climate change condition of Rewa district were studied during Kharif 2016-17 (Table 1). The findings on the beginning of white fly infestation were recorded in the 5^th week of July with an average population of 2.13 N&A /plant. However, during the month of July the average weekly population of the pest varied from 0 to 2.13 N&A /plant. The higher numbers of white fly population was observed in the month of August, with a record of peak population of 10.93 N&A /plant in the 4^th week of August. Of course, during the entire month of August the average weekly population of the pest was found changing between 4.20 to 10.93 N&A /plant. The white fly population the present climatic condition of Rewa district had indicated a decline in pest number from 1^st week of September and completely disappeared in the 1^st week of October (Table 1). The findings of (Nitharwal et al., 2013) has indicated it’s appearance from first week of August and reported peak population 11.20 N&A /plant of the pest in the month of September of Kharif  2006 and 2007. The correlation study of white fly population with the meteorological parameter viz., Temperature, relative humidity and rainfall had indicated a negative correlation (r = -0.322, -0.183, -0.001) with the maximum and minimum relative humidity and rainfall while a weak positive correlation (r = 0.101, 0.314) with maximum and minimum temperature. The temperature and sunshine hours also favourable for white fly population with positive correlation. These findings are in accordance with the findings of Yadav et al., (2015). In the present investigation peak of white fly population occurred in the 4^th week of August which indicate a changing pattern in its appearance and peaks, which in presently show the effect of climate change. While, the beginning of aphid infestation was recorded in the 2^nd week of August with an average population of 2.40 N&A /plant. However, during the month of August the average weekly population of the pest varied from 0 to 7.46 N&A /plant. The higher numbers of aphid population was observed in the month of September with a record of peak population of 12.40 N&A /plant in the 2^nd week of September. Of course, during the entire month of September the average weekly population of the insect was found changing between 2.93 to 12.40 N&A /plant. The aphid population in present climatic condition of Rewa district had indicated a decline in pest number from 3^rd week of September and completely disappeared in the 1^st week of October (Table 2). Similarly (Jat et al., 2017) also reported that the aphid infestation began in the 3^rd week of August (33^rd SMW) during the years 2013 and 2014 with peak population in the 1^st week of September (36^th SMW) during 2013 and 2^nd week of September (37^th SMW) during 2014 in Udaipur district of Rajasthan state. The correlation study of aphid population with the above mentioned meteorological parameter had indicated a negative correlation (r = -0.287, - 0.042, - 0.062) between the maximum and minimum relative humidity and rainfall while a weak positive correlation (r = 0.256, 0.266) with maximum and minimum temperature. Jat et al., (2017) also reported that the aphid population decreased due to excessive rainfall (94.80 mm/week) and relative humidity (87.60%). The present finding also show an excessive rain (94.80 mm/week) during the 2^nd week of September. Abiotic factors like temperature, relative humidity, extent and distribution of rainfall, sunshine hour etc. influenced the infestation and stabilization of various insect pests in cowpea (Kumar and Kumar, 2015).
 

 

 
Diversity of insect pests on Black gram in Rewa district
 
The incidence of ten insect pests on the crop from germination to harvesting stages (Table 2). The insects which appeared on the crop were from Lepidoptera, Hemiptera, Coleoptera Diptera and Thysanoptera order and their incidence were noted from 5^th week of July to harvesting of crop. White fly incidence was recorded earliest i.e. 5^th week of July and its infestation continued up to 4^th week of September. Jassid was recorded on the crop from 5th week of July to 4^th week of September. Aphid infestation on black gram in district Rewa were recorded in 2^nd week of August and continued up to 4^th week of September. The Bihar hairy caterpillar as a defoliating pest recorded its first appearance on the crop in the existing 4^th week of August and continued up to 1^st week of October. Among the defoliating insects Tobacco caterpillar appearance was recorded from 1^st week of August to 1^st week of October. Stem fly was recorded as borer insect in the crop and its 1^st appearance was recorded in the 3^rd week of August at seedling stage of the crop and continued the infestation up to growth stage of the crop during Kharif 2016-17. At the pod stage of the crop Riptortus bug appearance was recorded from 4^th week of August to 4th week of September and Green stink bug appearance was recorded from 1^st week of August to 4^th week of September. At the flowering stage of the Blister beetle incidence was recorded in high number from 3^rd week of August to 2^nd week of September. Flower thrips incidence was recorded on the crop from 3^rd week of August to 2^nd week of September. The composition of black gram insect pests has also been studied by various workers in different parts of country. (Chandra et al., 2010) reported sixteen insect pests population associated with urd bean [Vigna mungo (L.) Hepper] at different stages of crop grown from Faizabad Uttar Pradesh, India.

Diversity of natural enemies of insect pests in Black gram crop field
 
This study indicated (Table 2) the presence of six natural enemies in the crop ecosystem under the climate condition of Rewa district on black gram variety T-9. This arthropod was found belonging to class arachnids (i.e. spider) and class Insecta. The dominating species from the class Insecta were lacewing, lady bird beetle, dragon fly, damsel fly and preying mantid during Kharif 2016-17.
 
The studies conducted earlier in the country also indicated the presence of the predatory coccinellids in Black gram [V. mungo] feeding on Aphis craccivora in pulses (Parasuraman, 1989 and Routray et al., 2016). (Kedar et al., 2014) reported Cheilomenes sexmaculata (Fabricius) and Brumoides suturalis (Fabricius) as the most common predator of whitefly, Bemisia tabaci (Gennadius) on urdbean from Hisar, Haryana.
 
Efficacy of eight insecticides was evaluated against white fly after one day, 3,7,10 and 15^th day of the insecticide spray.
 
White fly
 
The post treatment effect indicates (Table 3) that one day after the treatment a significant reduction in the population of insect pests was noted in the insecticide treated plots than control. The average number of insects varied from 4.03 to 6.3 Nymph and Adult/plant in insecticide treated plots as against 12.93 Nymph and Adult/plant of untreated control. A significance influence of the insecticide was further seen after 3^rd and 7^th day of the treatment with a ranging population between 1.97 to 4.43 and 0.97 to 3.3 Nymph and Adult/plant, respectively. Among the tested insecticides, Thiacloprid @ 60 g a.i./ha was found superior over the rest of the insecticides with a percent reduction of 88.07 % in insect population after 7^th day which was followed by Thiomethoxam @ 25 g a.i./ha with a reduction of insects population of 87.70 %. After 15^th day of insecticide treatment a slight increase in the pest population were seen in all the insecticide treated plots including untreated control. Sunil et al., 2015 also found similar result in their studied.
 

 
After second spray of insecticide, no doubt, further reduction in white fly population was observed in various treatments with a record of 2.57 to 4.07 Nymph and Adult/plant in comparison to untreated control (10.97 Nymph and Adult/plant), one day after the second spray. A significance influence of the insecticide was further seen after 3^rd and 7^th day of the treatment. At this stage the population varied between 1.37 to 3.2 and 0.73 to 2.4 Nymph and Adult/plant, respectively. However, the populations in untreated control were found consequently higher. Among the tested insecticides Thiacloprid @ 60g a.i./ha was found superior over the rest of the insecticides with a percent reduction of 89.86% in insect’s population after 7 days which was followed by Thiomethoxam @ 25g a.i./ha with a reduction of 88.33%. All insecticide were found effective and significantly superior over control after fifteen day of the second treatments. Similar results were observed by several workers in the past. The following order of the efficacy of the insecticides, in the descending order, was observed T₃ (Thiacloprid @ 60 g a.i./ha) >T₇ (Thiomethoxam @ 25 g a.i./ha) > T₈ (Emamectin benzoate @ 11g a.i./ha) > T₅ (Flubendiamide + Thiacloprid @ 60+60 g a.i/ha) > T₁ (Flubendiamide + Thiacloprid @ 48+48 g a.i/ha) > T₄ (Chlorantraniliprole @ 30 g a.i /ha) >T₆ (Quinalphos @ 375 g a.i./ha) > T₂ (Flubendiamide @ 60 g a.i./ha). (Rajawat et al., 2017) also reported Thiacloprid 21.7% SC was found significantly very effective against white fly.
 
Aphid
 
Efficacy of above mentioned insecticides against aphid indicated (Table 4) effectiveness of all insecticide over the untreated control. The post treatment effect, after one day, indicated a significant reduction in the population of insect in the insecticide treated plot than untreated control. The average number of insects varied from 6.3 to 8.53 Nymph and Adult/plant in insecticide treated plot as against (13.7 Nymph and Adult/plant) of untreated control. A significance reduction in the pest population due to insecticide treatment was further seen after 3^rd and 7^th day of the application with a record of 4.8 to 7.06 and 4.37 to 6.8 Nymph and Adult/plant, respectively. However, the populations of untreated control consequently, were found at 10.2 Nymph and Adult/plant and 10.7 Nymph and Adult/plant. Among the tested insecticides Thiomethoxam @ 25 g a.i./ha was found superior over the rest of the insecticides with a percent reduction of 59.16 % in pest population after 7^th day; followed by Emamectin benzoate @ 11 g a.i./ha 54.86 %. However, after 15^th day of insecticide application a further increase in the pest population was seen in all the insecticide treated plots.
 

 
After second spray of insecticide further reduction in aphid population was seen in various treatments in comparison to untreated control. In the insecticide treated plots population of aphid was observed between 4.8 to 7.2 Nymph and Adult/plant as against 11.98 Nymph and Adult/plant in untreated control one day after the second spray. A significance influence of the insecticide was further seen after 3^rd and 7^th day of the treatment, with a record of 3 to 5.1 and 1.2 to 3 Nymph and Adult/plant population, respectively. However, the population in untreated control, consequently, was found 12.19 and 10.3 Nymph and Adult/plant. Among the insecticides, Thiomethoxam @ 25g a.i./ha was found superior over other insecticides with a record of 88.24 % reduction in population followed by Emamectin benzoate @ 11g a.i. /ha 84.43% after 7^th day  of spraying. Similar results were finding by (Parmar et al., 2015) and (Yadav et al., 2015). The following order of the efficacy of the insecticides, in the descending order, was observed  T₇ (Thiomethoxam @ 25 g a.i./ha) > T₈ (Emamectin benzoate @ 11g a.i./ha) > T₃ (Thiacloprid @ 60 g a.i. /ha) > T₅ (Flubendiamide + Thiacloprid @ 60+60 g a.i. /ha) > T₁ (Flubendiamide + Thiacloprid @ 48+48 g a.i. /ha) > T₄ (Chlorantraniliprole @ 30 g a.i /ha) > T₂ (Flubendiamide @ 60 g a.i. /ha) > T₆ (Quinalphos @ 375 g a.i. / ha).
 
Effect on grain yield and cost benefit ratio

The highest yield of 1008.0 kg/ha,was recorded in the plot treated with Thiacloprid @ 60 g a.i. /ha followed by Thiomethoxam @ 25 g a.i. /ha (984.0 kg/ha) as against the yield of 560 kg/ha  in untreated control. 

An increase in yield due to insecticide treatment has been reported by various scientists at national and global level. (Sharma and Singh, 2015) found that significantly higher yield in 2012 due to Imidacloprid treatment (11.33 q/ha) followed by Thiomethoxam (10.88 q/ha). In the year 2013, Thiomethoxam gave better results in increasing the yield 11.93 q/ha than other tested insecticides. The maximum C:B ratio (1:16.7) was recorded from Thiomethoxam treatment followed by Thiacloprid (1:13.3).