Seasonal Abundance of Spotted Pod Borer, Maruca vitrata Fabricius in Early Pigeonpea [Cajanus cajan (L.) Millsp.] and its Management through Farmscaping in Uttar Pradesh

India is one of the leading producers of pigeonpea in the world with a production of 41.80 Lac tonne during 2017-18. Among the major pigeonpea producing states, Uttar Pradesh occupies fifth position (7.25%), with a production of 3.03 Lac tonne during 2017-18 (Anonymous, 2018). The national productivity of pigeonpea is 937 kg/ha. Developing early maturing varieties / hybrids with high yielding potential is the prerequisite for increasing the productivity. The spotted pod borer, Maruca vitrata Fabricius is a key insect pest that causes severe yield loss of up to 68 per cent in early maturing pigeonpea genotypes (Sharma and Franzmann, 2000). Singh (1999) has reported a yield loss of 70-80 per cent in pigeonpea at Bangalore, India. A similar loss in pigeonpea was also reported from Dindigul, Tamil Nadu also (Kumar and Pavviya, 2018). Short duration pigeonpea recorded higher pod damage by M. vitrata (32%) than gram pod borer, Helicoverpa armigera (Hubner) Hardwick (4%), pod bugs and blister beetle in Uttar Pradesh (Sujayanand and Saxena, 2013). The M. vitrata larvae have a typical habit of feeding inside webs. The larva produces a silken web for spinning the leaves, flower-buds, developing flowers and pods and it starts feeding the reproductive parts of the plant. Often, the larva pupates inside the web. Thus, the entire larval and pupal stage is protected from the external environment and insecticides by the silken web (Sharma, 1998). Some of the insecticides like methomyl failed to control M. vitrata population in soybean at Brazil (Grigolli et al., 2015). Hence there is a need to have sustainable management through Farmscaping approach. Pigeonpea genotypes having determinate and cluster flowering habit is found to be highly susceptible to M. vitrata infestation (Sunitha et al., 2008; Saxena et al., 1996). M. vitrata is a serious pest in many leguminous crops like cowpea, black gram, green gram, field bean etc (Sonune et al., 2010; Randhawa and Saini, 2015). This insect pest has a wide geographic distribution with a prominent occurrence in Semi-arid tropical countries (Margam et al., 2011). Hence, there is a need to understand the pest population dynamics, micro-climatic requirements and its natural enemies for devising a sustainable management technique through integrated pest management. In order to modify the microfauna and microclimate of cropping environment, farmscaping strategy was chosen in the present investigation. Border crops were selected based on its ability to perform as refugia plant i.e. it will enhance the natural enemy activity and thereby suppress the pest. Further, knowledge of M. vitrata incidence and the weather factors favouring the population flare up or abundance is very much essential for planning the prophylactic spray schedule to control M. vitrata population and its damage. The present study was devised to identify a suitable border crop which can modify the micro-climate in such a way that enriches natural enemies and concurrently diminishes the pest population in sustainable way. Further, the present investigation was also designed to identify the weather factors that influence the population build up of M. vitrata. So, that prophylactic spray with suitable biopesticide can be done before onset of the favourable weather.

A field trial on early pigeonpea (variety ICPL67B) was conducted in ICAR-Indian Institute of Pulses Research, Kanpur for management of spotted pod borer, M. vitrata by deploying 7 different border crops (Cluster bean, Green gram, Black gram, Cowpea, Daincha, Sorghum and Pearl millet) during Kharif 2014 to 2017. The individual plot size measured, 7 x 5 m and it was laid out in randomized block design with 8 treatments replicated thrice. Each block was separated by 2 m apart and 1 m alley was present between the plots. The pigeonpea variety ICPL67B was sown in Kharif season (23^rd to 24^th standard meteorological week (SMW)) during four consecutive years (Kharif 2014 to 2017) with spacing of 60 X 30 cm. Two rows of border crops (60 cm distance between rows) either cluster bean (Cyamopsis tetragonoloba L. Taub.) or green gram [Vigna radiata (L.) Wilczek.] or black gram [Vigna mungo (L.) Hepper] or cowpea [Vigna unguiculata (L.) Walp.] or daincha [Sesbania aculeate (Willd.) Pers.] or pearl millet [Penisettum glaucum (L.) R.Br.] or sorghum [Sorghum bicolour (L.) Moench] was sown in all 4 sides of pigeonpea during 29^th to 30^th SMW of every year. Recommended agronomic package of practices were followed to raise a healthy crop. The entire experimental plot was exposed to natural infestation of insect pest and natural enemies by not spraying any insecticides during the entire crop growing period. Fixed-plot sampling technique was followed for recording the incidence of M. vitrata larval webbings and its major natural enemies in different plots. Ten pigeonpea plants were randomly selected and tagged in each plot for recording insect population at weekly intervals. Yield data were recorded plot wise and mean was calculated for each year. Data analysis was done by using SAS 9.1 software.
 
To find out the role of different weather parameters that influence the seasonal abundance of M. vitrata in Kanpur and to assess its contribution, multiple regression was performed by considering the Maruca larval population (ML) as dependent variable (Y) and the six weather parameters [day length (h), maximum temperature T max (°C), minimum temperature T min (°C), rainfall (mm) and relative humidity (RH %)] as independent variable (X) for the corresponding years. The weather data during four years (Kharif 2014 to 2017) were recorded from the automatic weather station [AWS, Field Climate METOS^® Pessl Instruments GmbH, Austria] maintained at Division of Basic sciences, ICAR-IIPR and weekly mean for each weather parameter was calculated.
 
ML= b₀ + a (Day length) + b (Rainfall) + c (T min) + d (T max) + e (RH)
 
Where
b₀ is intercept; a, b, c, d and e are regression coefficients of respective weather parameter mentioned above.

Incidence of spotted pod borer webbing
 
The pooled mean of M. vitrata larval webbing per plant in pigeonpea (ICPL67B) during Kharif 2014 to 2017, ranged from 2.05 to 5.78 (Table 1). The highest (5.78) larval webbing per plant was recorded from cowpea (T₄) as border crop with pigeonpea which was on par with sole crop (T₈:5.25) while the lowest (2.05) was recorded from sorghum (T₇) as border crop with pigeonpea. Among the four years, two years i.e. Kharif 2017 (8.81) and 2015 (2.49) had recorded highest larval webbing from T₈; while Kharif 2016 highest C. septumpunctata followed by cowpea (555.6). The possible reason may be due to high incidence of aphids in sorghum compared to cowpea.
 

 

 

 
Activity of spider
 
The predominant spiders found in different treatments were Oxyopus sp, Clubiona sp, Thomisus sp and Araneu sp. The highest (0.76) spider population per plant was recorded from pigeonpea having sorghum as border crop (T₇) followed by pearl millet (0.45) (Table 4). Further, the sorghum (T₇) has recorded significantly highest spider population among the 8 treatments studied. The sorghum as border crop has recorded significantly higher spider population per pigeonpea plant during 2015 (0.69), 2016 (0.78) and 2017 (1.2). The present result supports the findings of Gopali et al., (2010) where they reported that spider population was the highest in sorghum intercropped pigeonpea (1.25/plant) followed by bajra intercropped pigeonpea (1.05/plant). The sole crop (T₈:0.10) has recorded the lowest spider population per plant and was on par with treatments (T₁:0.30; T₂:0.35; T₃:0.14; T₄:0.16 and T₅:0.07). Singh et al., (2013b) also reported that spider population (0.75/plant) was more in pigeonpea + rice intercrop than sole crop and other treatments. The present finding is in agreement with Solanki and Kumar (2015). They found highest spider diversity in maize crop followed by pigeonpea. In the present study the sorghum and pearl millet belongs to same family (Poaceae) and crop geometry as that of maize which in turn might have enhanced spider population in those treatments. The present result is in agreement with Khajuria et al., (2015); wherein the occurrence of predatory spider was reported in pigeonpea agro-ecosystem.
 

 
Yield
 
The sorghum as border crop with pigeonpea has recorded significantly highest pooled yield of pigeonpea (730.72 kg/ha) among the 8 treatments. The second highest yield was recorded from green gram as border crop with pigeonpea (517.79 kg/ha) followed by cluster bean (494.25 kg/ha) and pearl millet (487.58 kg/ha). Also, similar trend was observed in per cent increase in yield over sole crop. The highest percent increase in yield (Fig 1) was recorded from sorghum (65.81%) followed by green gram (17.49%), cluster bean (12.15%) and pearl millet (10.64%). The pulse intercropping with monocots such as sorghum always enhances the yield. The present finding is in accordance with Prasad et al., (2011) wherein they had reported pigeonpea + sorghum cropping system as most remunerative cropping system among the four different intercropping systems they had evaluated. A similar report of the lowest per cent fruit damage in brinjal by L. orbonalis was found when it is planted with maize as border crop and coriander as intercrop as reported by Sujayanand et al., (2015). Thus, the graminaceous crops (like sorghum or maize or pearl millet) act as wind shield and it restrict the movement of adult moths by mechanical means. Apart from mechanical hindrance some of the plants like sorghum, maize, etc offers pollen and nectar for the predaceous coccinellids that act as refugia for them, the predators, in turn, suppress the neonate larvae present in main crop. Thus, indirect biological control service and mechanical hindrance provided by these refugia crops results in the lowest pod damage and thereby increases the pod yield.


 
Influence of abiotic factors on seasonal abundance of M. vitrata larvae
 
The Maruca larval population was noticed from 41^st SMW to 47^th SMW in Kanpur for the four years of study except 2016; wherein the infestation started from 40^th SMW to 41^st SMW (Fig 2) according to prevailing weather condition of the year. The peak larval population was recorded on 46^th SMW (8.00/plant) and 44th SMW (13.33/plant) during 2014 and 2017 whereas during Kharif 2015 and 2016, peak population was recorded in 41^st SMW (5.13/plant and 9.67/plant). A similar finding of peak Maruca larval webbing (24.00; 24.88 and 25/plant) in 40^th SMW during Kharif 2015-2017 was reported from Ludhiana (30.9010° N, 75.8071° E) by Taggar et al., (2019). Except for the Kharif 2017 (4 week difference) there was a difference of 1 week in peak Maruca larval webbing between Ludhiana (40^th SMW) and Kanpur (41^st SMW).  The present finding is not in agreement with Chaitanya et al., (2012) and Sampathkumar and Durairaj (2015); wherein they had reported peak M. vitrata population (17.3/plant and 9.38/plant) during December (49^th SMWand 50^th SMW). The probable reason may be due to differences in weather parameters like prevalence of longer day length and higher minimum temperature in December in their study location i.e. Tirupathi (13.6288° N, 79.4192° E); Coimbatore (11.0123° N, 76.9355° E) than our study location i.e. Kanpur (26.4932° N, 80.2742° E).It can be inferred from the present report along with Taggar et al., (2019) and Chaitanya et al., (2012) that the peak larval population of Maruca is gradually shifting from North India to South India, during its course of time from September towards December. It appears that M. vitrata is migrating from North to South India during winter progression in India. A similar kind of M. vitrata migration was already reported in Western Africa by Ba et al., (2009). In spite of the South-North migration occurrence in Western Africa there was a reduced gene flow in M. vitrata populations (Agunbiade et al., 2012).


        
The regression coefficients observed for day length, rainfall, minimum temperature, maximum temperature and RH was 1.53,-0.02,-0.35,-9.05 and -0.12 respectively. The results on regression analysis (Table 5) yielded the following equation and showed that the 6 weather parameters together explained the variation in Maruca larval population (ML) by 41% (R²=0.41).
 

 
ML= 33.14 + 1.53 (Day length) -0.02 (Rainfall) -0.35 (T min) -9.05 (T max) -0.12 (RH)
 
Out of 6 weather parameters studied, RH was found to influence the ML significantly. If the other weather parameters were at their mean level a unit rise in RH will decrease the larval population by 0.12 times. The second most influencing weather parameter was day length. A unit increase in day length will result in increased ML by 1.53 times. The present result corroborates with that of Sreekanth et al., (2015) wherein they observed significant correlation between M. vitrata population and sunshine hours (0.656) and evening relative humidity (RH-II) (-0.609). Research has shown that lack of rain, relative humidity and temperature may influence seasonal abundance of M. vitrata (Agunbiade et al., 2012). The present finding supports Sampathkumar and Durairaj (2015); who also had reported that five weather parameters including sunshine hours (1.495 times) had significantly influenced M. vitrata population in pigeonpea at Coimbatore.

The present study concludes that the sorghum and pearlmillet as a border crop (2 rows) with pigeonpea (ICPL67B) has resulted in the lowest incidence of spotted pod borer, M. vitrata larval webbing and at the same time higher activity of its natural enemies viz., C. sexmaculata, C. septempunctata and spiders. Further sorghum as border crop with pigeonpea has recorded highest yield among the 8 treatments (Cluster bean, Green gram, Black gram, Cowpea, Daincha, Sorghum, Pearl millet and sole crop) tested. Hence this farmscaping system can be well fitted in integrated pest management package designed for spotted pod borer management in short duration pigeonpea. Further, relative humidity and day length exerted significant influence on the Maruca larval webbing in Kanpur. The Maruca incidence started during 41^st SMW every year. Hence, by planning a prophylactic insecticidal spray before the onset of favourable weather or Maruca incidence will be helpful for successful management of the insect pest.

The authors like to acknowledge the assistance of Dr. Hem Saxena in identifying the natural enemies of M. vitrata. The authors wish to pay their gratitude Dr. P.S. Basu, Divison of Basic Science, ICAR-IIPR, Kanpur, for generous sharing of weather data and Dr. N.P. Singh Director, ICAR-IIPR, Kanpur for his consistent support and encouragement in providing the facilities during this project implementation.

The project was financially supported by ICAR-IIPR, Kanpur. [Project code: CRSCIIPRSIL 201301000089].

Dr. Sujayanand, G.K. conceived, planned and executed the experiment. Dr. Anup Chandra edited the manuscript. Sonika Pandey assisted in data collection. Dr. Sriphad Bhatt and Dr. Anup Chandra assisted in data analysis and preparation of graphs.