Management of Gram Caterpillar, Helicoverpa armigera (Hubner) with Bt Formulation in Chickpea under Organic Conditions

Chickpea (Cicer arietinum L.) also known as gram, Bengal gram, Egyptian pea, garbanzo, garbanzo bean and chana. It is an important legume crop among the various pulses which is also a good source of protein and belongs to the family Fabaceae, subfamily Faboideae (Jukanti et al., 2012). Depending upon its shape, size and colour of seeds, chickpea is divided into two types, viz. desi and kabuli. Gram contains 59.6% carbohydrates, 24% protein and 3.2% minerals (Bakr et al., 2004). Chickpea also improves the fertility of the soil by fixing the atmospheric nitrogen besides its importance as human and animal feed. Initially about 7000 years ago chickpea was introduced in the Middle East for the first time and in present time this crop is popular in 40 countries. Among these major chickpea growing countries are India, Turkey, Pakistan, Iran, Mexico, Australia, Ethiopia, Myanmar, and Canada. Global production of chickpea is 13.10 million tons from an area of 13.54 million hectares with the productivity of 968 kg/ha (FAOSTAT, 2015).     
       
Different biotic and abiotic stresses lead to drastic reduction in the production and productivity of chickpea. This crop is vulnerable to a wide range of insect-pest and diseases. Majorly eleven insect- pests have been reported to cause huge losses to the chickpea crop (Rahman et al., 1982). Among different insect pests, gram caterpillar, Helicoverpa armigera (Hubner) is a serious pest of the chickpea. Larvae of this pest feed upon leaves, flowers and pods in chickpea crop that results in huge loss reaches upto 90% in the fields (Ahmad et al., 2015).
       
Gram caterpillar is a cosmopolitan and widely distributed insect pest in the world. It attacks nearly all legume crops and causes huge losses to these crops. Besides chickpea, H. armigera is also major pest on cotton, pigeonpea, sunflower, corn, chilli, tomato and okra (Wubneh, 2016). In India, gram caterpillar attacks nearly 181 legume species (45 families) that including both cultivated and uncultivated ones. This insect is reported from different regions of the world that including Palearctic, Oriental, Ethiopian and Australian provinces. It survives in different climatic conditions viz., Tropical, Dry and Temperate (CAB, 2000).
       
In chickpea and other legumes 1^st, 2^nd and 3^rd instar larvae feed on the young leaves of the plant whereas in cotton and pigeonpea the larvae feed on the flowers and flower buds. Along with the development, larvae shift from foliage to developing seeds and fruits (Reed and Pawar, 1982). Young seedlings of chickpea may be destroyed completely specially under tropical climatic conditions in southern India. The later larval instars bore into pods/bolls and consume the developing seeds inside the pod (Patil et al., 2017).
       
Chemical insecticides are commonly used for the management of H. armigera but heavy dependence on chemical insecticides have resulted into the development of resistance in this insect (Kranthi et al., 2002; Yang et al., 2013; Bird, 2018). Along with development of resistance, excessive use of insecticides is also harmful to different beneficial arthropods, non-target organisms and human health (Mesnage and Seralini, 2018). The high use of chemical insecticides can be effectively reduced by integrating biopesticides in different pest management programs for H. armigera. The use of biopesticides is effective and environmentally safest method for the management of H. armigera (Abid et al., 2020).
               
Bacteria based insecticides are specific for the target insect-pests and do not harm the beneficial organisms like parasitoids and predators. Due to the development of more effective strains of Bacillus thuringiensis (Bt) and its improved commercial formulations, these biopesticides are getting more international support for its use against agriculturally important insect-pests. Similar attempts were made in the present studies to evaluate the Bt based biopesticide for the management of gram caterpillar in chickpea.

In the present investigations the recommended variety of chickpea, i.e., PBG 5 was grown under organic conditions at Organic Research Farm, Punjab Agricultural University (PAU) at Ludhiana in Punjab. As per PAU Package of Practices for Rabi crops, the chickpea crop was sown over total area of 480 m² (5 m x 4 m replicated plot size). Chickpea seed quantity was used as per recommendation (15-18 kg/acre) at 30 cm row to row spacing during 1^st fortnight of 5-10 November in 2019-20 and 2020-21 (Anonymous 2021). Also, 1.20 tonnes of farm yard manure was applied in the field to fulfill the nutrient requirement of the crop. The seed was moistened in water and inoculated with recommended quantity of Mesorhizobium (LGR-33) and Rhizobacterium (RB-1) biofertilizers before sowing. The Bt based biopesticide, B. thuringiensis var. kurstaki 0.5 WP (DOR Bt 1) was applied @1.5, 1.75 and 2.0 kg/ha for the management of H. armigera on chickpea on 2018-19 and 2019-20. An untreated control was also kept for the comparison. A total of three replications were kept during experimentation. The first biopesticide spray was applied at pod initiation and second at 15 days thereafter. The observations were recorded on the larval population as the number of larvae per metre plant row after 7 and 15 days of the spray. The per cent pod damage was worked out based on number of damaged pods by taking a random sample of 200 pods per plot per replication at harvest time. Grain yield data were also recorded from each plot after harvest and calculated to per hectare basis. The data were analyzed by Randomized Block Design and square root transformations using computer programme CPCS1 (Cheema and Singh 1990).

All the biopesticide treatments showed better performance than the untreated control in terms of larval population, pod damage reduction and yield gain. The detailed results have been presented below:
 
Larval population
 
The average larval population of H. armigera varied significantly from 1.19-3.20 per 5 plants in different treatments, including the untreated control (Table 1). Based on pooled mean of both years, all treatments performed significantly better than untreated control after seven and fifteen days of spray. At 7 DAS, pooled sum of two sprays of DOR Bt-1 @2.0 kg/ha revealed significantly better due to low larval counts of gram caterpillar (0.87 larvae/ metre plant row) than its lower dosages @ 1.75 kg/ha (1.31 larvae/ metre plant row) and 1.5 kg/ha (1.44 larvae/ metre plant row) and the untreated control where significantly higher larval population (2.56 /metre plant row) was recorded. At 15 DAS, in DOR Bt-1 @2.0 kg/ha significantly lower larval counts was recorded (1.19 larvae/ metre plant row) based on pooled sum of two sprays than its lower doses, i.e. 1.75 kg/ha (1.54 larvae/ metre plant row) and 1.5 kg/ha (1.79 larvae/ metre plant row) as compared to the untreated control (3.20 larvae/ metre plant row). The present investigations are in agreement with those of Gudipati and Mondal, 2020) who also registered low larval population in Bt treated plots (0.32 larvae/ plant) as compared to untreated control (0.78 larvae/ plant). They also recorded higher yield in Bt treated plots (1.95 t/ha) over untreated control (1.33 t/ha) which also supports the present work. Similarly, findings by Taggar et al., (2014) that lowest larval population in native Bt isolate @ 1.5 kg/ha (3.66/plant) and Bt-1 @1.5 kg/ha (3.66/plant) over the untreated control (5.87/plant) also supports the present studies for lower pest population in Bt formulation.
 

At 7 DAS, the DOR Bt-1 @2.0 registered higher per cent reduction of larvae over control (66.02%) than its lower dosages of 1.75 kg/ha (48.83%) and 1.5 kg/ha (43.75%). At 15 DAS, DOR Bt-1 @2.0 kg/ha performed better with per cent reduction of larvae (62.81%) than its lower dosages of 1.75 kg/ha (51.88%) and 1.5 kg/ha (44.06%). The studies by Gudipati and Mondal (2020) that 59.40 per cent reduction of H. armigera larvae due to Bt on chickpea have supported the present findings. Similarly, Allahyari et al., (2020) who reported 59.82 per cent larval reduction of H. armigera larvae by B. thuringiensis subsp. kurstaki (Btk) in chickpea also falls in the range of larval reduction during present work.
 
Pod damage
 
The pod damage ranged from 3.28 to 25.30 per cent in all the treatments including untreated control in both the years (Table 2). The pod damage in DOR Bt-1 @2.0 kg /ha (3.28%) was significantly lower as compared to its lower doses, i.e., DOR Bt-1 @1.75 kg /ha (4.95%) and DOR Bt-1 @1.5 kg /ha (5.79%) during 2018-19. Similar trend was observed for pod damage during 2019-20, i.e., lower pod damage in DOR Bt-1 @2.0 kg/ha (4.00%) than its lower dosages, i.e., DOR Bt-1 @1.75 kg/ha (11.00% and DOR Bt-1 @1.5 kg/ha (17.00%). Based on overall mean, DOR Bt-1 @2.0 kg/ha was better with lowest pod damage (3.64%) than its lower dosages-DOR Bt-1 @1.75 kg/ha (7.98%) and DOR Bt-1 @1.5 kg/ha (11.40 %). Highest pod damage reduction recorded during 2018-19 and 2019-20 was 68.09 and 84.19 per cent in DOR Bt-1 @2.0 kg /ha than its lower dosages. On overall mean basis, DOR Bt-1 @2.0 kg /ha recorded highest pod damage reduction (76.14%) than at its lower dosages, i.e., DOR Bt-1 @ 1.75 kg /ha (54.18%) and DOR Bt-1 @1.5 kg/ha (38.24%).
 

The present studies for pod damage in chickpea are in agreement with findings by Chaudhary and Sharma (1982) who reported 7-10 per cent pod damage in chickpea due to single larvae of H. armigera that resulted in 5.4 per cent yield loss. Russel et al., (1999) recorded an average 10-30 per cent chickpea yield loss on account of damage caused due to H. armigera, and this is in accordance with the present work. A work from Pakistan, by Sarwar et al., (2009, 2011) who reported 26.01 to 40.08 and 10.53 to 39.14 per cent losses due to H. armigera on susceptible and tolerant genotypes from early vegetative to fruiting stage on chickpea, respectively, also supports the current findings. In a study, Bt based insecticides-Biobit, Delfin and DiPel together with NPV recorded low pod damage due to H. armigera in chickpea (4.2 to 16.7%) over the untreated control (12.4 to 38.6%) (Anonymous, 1997) have also supported present findings. Similarly, the research findings by Taggar et al., (2014) in Punjab regarding the low pod damage (25.57%) by H. armigera in Bt-1 @ 1.5 kg/ha over untreated control (39.45%) in pigeonpea are in accordance with present studies. The present work is in agreement with Allahyari et al., (2020) who reported 9.03 and 27.32 per cent pod damage in chickpea by H. armigera after 14 days of Bt treatment.
 
Yield
 
In 2018-19, DOR Bt-1 @2.0 kg/ha registered significantly highest grain yield (1317 kg/ha) than its lower dosages of 1.75 kg/ha (1126 kg/ha) and 1.75 kg/ha (1073 kg/ha) over untreated control (903 kg/ha) (Table 3). In 2019-20, similar trend was observed with higher yield in DOR Bt-1 @ 2.00 kg/ha (1233 kg/ha) than its lower dosage of 1.75 kg/ha (1003 kg/ha) and 1.50 kg /ha (925 kg/ha) over the untreated control (857 kg/ha). On overall mean basis for two years, DOR Bt-1 @2.00 kg /ha performed better due to highest yield (1275 kg/ha) than lower dosage of 1.75 kg/ha (1065 kg/ha) and 1.5 kg/ha (999 kg/ha) over the untreated control (880 kg/ha). Similarly, the present investigations for higher yield in chickpea in the studies for management of gram caterpillar on chickpea crop are in agreement to those of Ahmed and Khalique (2012) and Taggar et al., (2014) who also reported highest yield of pigeonpea in Bt treated plots over the untreated plots. The present work is in agreement with Allahyari et al., (2020) who in their studies for management of H. armigera with Bt formulation also recorded higher yield in Bt treated plots (786.42 kg/ha) over the untreated plots (627.49 kg/ha).
 

The non-judicious use of chemical pesticides created various issues like development of pest resistance, resurgence and residue effects on soil, water and environment besides ill effects on human and animal. The task of resistance development is more frequent in Helicoverpa armigera (Hubner) in comparison to other insect pests. Furthermore, untimely and excessive pesticidal applications can lead to the residual problems in H. armigera on chickpea. The detection of different ecofriendly pest management strategy is the only solution to the earlier mentioned problems. In view of that Bt formulation was tested against H.armigera on chickpea crop under organic conditions in the present investigation. The finding of present work revealed low larval counts of H. armigera larvae, pod damage, highest per cent larval reduction and more crop yield in Bt treated chickpea plots (DOR Bt-1 @2.0 kg/ha) over untreated ones. Therefore, the tested Bt formulation was observed to have high potential for the management of H. armigera in chickpea crop under organic conditions.

There is no conflict of interest for the present investigations.