Chickpea, Cicer arietinum is an important rabi pulse grown all over the world. India is the single largest producer of chickpea accounting for 65 per cent of the total production (FAOSTAT, 2017). Insect pests are the major limiting factors in chickpea production. It is known to be attacked by about 60 insect-pests (Reed et al., 1987), which causes 15% yield loss annually. Among these Chickpea pod borer (CPB), Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) is the most notorious insect pest. Yield losses due pod borer damage in chickpea may range from 70 to 95% (Prakash et al., 2007). The increasing concern for environmental problems that are created by the use of toxic pesticide, development of high-level resistance in Helicoverpa to the conventional insecticides (Kranthi et al., 2002) has promoted a worldwide interest in the adoption of ecological basis of pest management. Biological control is one important tool of Integrated Pest Management that utilizes the contribution of natural enemies to reduce pest population. The ichneumonid, endo-larval parasitoid Campoletis chlorideae (Uchida) recorded to be the most effective natural enemy of, Helicoverpa armigera on chickpea. Campoletis chlorideae (Uchida) was found to parasitize the early instars of Helicoverpa armigera. The parasitoid deposit eggs singly into first or second instar larvae and comes out from the host during third or fourth instar to spin a cocoon and pupation takes place on the plant inside the spun cocoon. In chickpea ecosystem this endo-larval parasitoid reported to cause 0.98 to 68.50 per cent parasitization of H. armigera (Kaur et al., 2000). Date of sowing has a great impact on the activity of pod borer as well as Campoletis due to environmental variation. Therefore, the present study was conducted to observe the effect of chick pea sowing time on natural parasitization of gram pod borer by Campoletis.

The present study was carried out in the Norman E. Borlaug crop research centre (NEB-CRC), G.B.P.U.A and T, Pantnagar to study the impact of abiotic factors and the different dates of sowing on Percent parasitization of Helicoverpa armigera by Campoletis chlorideae in chickpea ecosystem. The chickpea variety PG 186 was sown on three dates (20^th October, 11^th November and 1^st December) during 2017-18 in an area of 10m². Twenty-five larvae of H. armigera (first and second instars) were collected randomly at weekly basis from untreated chickpea crop. The collected Larvae were brought to the laboratory in plastic vials and reared individually in laboratory till the parasitoid emergence. Observations were recorded on number of adult parasitoid emerging from H. armigera larvae and per cent parasitization was computed. Simple correlation coefficient was derived between the per cent parasitization during a standard week and average maximum temperature, minimum temperature, maximum relative humidity and minimum relative humidity. To find out the individual as well as combined impact of the abiotic factors on the per cent parasitization was worked out using regression analysis. The statistical analysis was done using SPSS statistical tool.

Per cent parasitization of H. armigera in three different dates sown chickpea
 
In the present study the effect of different dates of sowing on seasonal parasitization of Campoletis chlorideae, a larval parasitoid on Helicoverpa was studied in chickpea ecosystem during 2017-18 and the results have been presented in Table 1. The first appearance of parasitoid was observed on 51^st standard meteorological week (S.W.) in all the three different dates sown crop. It was observed that mean seasonal parasitism by Campoletis on larvae of H. armigera was found to be 21, 43.5 and 34.5 per cent in early (20^th October), normal (11^th November) and late sown crop (1^st December), respectively. Higher parasitism of 80 per cent was occurred on 3^rd S.W. in normal sown crop as compared to the 48 per cent (2^nd S.W.) and 72 per cent (6^th S.W.) in early and late sown crop, respectively (Fig 1). The present results were in agreement with Bisane et al., (2008) who also observed the incidence of C. chlorideae from 51^st S.W. (17-23 December) until 3rd S.W. (15-21 January) and it reported to cause 8.11 to 11.54 per cent parasitization of Helicoverpa. Ojha et al., (2017) recorded the maximum natural parasitization of H. armigera by C. chlorideae as high as 51.67 and 56.67 per cent during 2010-11 and 2011-12, respectively.
 

Influence of abiotic factors on percent parasitization in H. armigera
 
The relationships between per cent parasitization and various abiotic factors were worked out through correlation and regression analysis. The perusal of the results reveals that the abiotic parameters mostly registered high level of significant association with the per cent parasitization data in early and normal sown crop compared to the low level of non-significant association in late sown crop (Table 2). In early and normal sown crop, it is observed that per cent parasitization by Campoletis had a highly significant negative correlation with maximum and minimum temperature compared to non-significant association in late sown crop. Whereas highly significant positive correlation was recorded between maximum and minimum relative humidity in early sown crop compared normal sown crop which recorded highly significant positive correlation in maximum relative humidity with per cent parasitization. Non-significant positive correlation was observed between minimum relative humidity in normal sown crop, maximum and minimum relative humidity in late sown crop with per cent parasitization. The result was in cogent evidence with Pillai et al., (2016) who observed the significant negative correlation between weather parameters and the population of the larval parasitoid with maximum temperature and minimum temperature. Whereas positive correlation was recorded with maximum relative humidity and minimum relative humidity during 2010-11 and 2011-12, respectively.



The multiple regression analysis of the per cent parasitization data with the abiotic factors for the three different dates sown crop reveals that the combined effect of all the meteorological parameters was statistically significant in early and normal sown crop as compared to non-significant up to 95% probability level in late sown crop as evident from the estimated values of ‘F’ (Table 3). Together all the weather factors were responsible for 90%, 57.9% and 30.5% variation in per cent parasitization in early, normal and late sown crop, respectively.

The abiotic factors and different dates of sowing were found to have high level of influence on the per cent parasitization by C. chloridae on H. armigera during the experimental period in tarai region. Maximum and minimum temperature had significant negative correlation with per cent parasitisation in early and normal sown crop compare to non significant negative correlation in late sown crop. Maximum and minimum humidity had significant positive correlation with per cent parasitisation in early sown crop.

The authors are grateful to Norman E. Borlaug crop research centre (NEB-CRC), G.B. Pant University of Agriculture and Technology for providing required facilities.