MATERIALS AND METHODS

The present experiments were conducted in farmers field at Alandurai and Thondamuthur during summer 2004, and winter 2004-05, respectively. The cultivar MECH 162 Bt and MECH 162 N Bt were sown with a spacing of 90x90 cm. The seeds were provided by Project Directorate of Biological control (PDBC), Bangalore. Each treatment was laid out in an area of 0.2 ha with four replications. The agronomic practices and application of FYM at the rate of 25 t ha^-1 was uniform for all treatments which was Tamil Nadu Agriculture University, Coimbatore, recommendations to maintain ideal crop stand (Anonymous, 1999). The different combinations of treatments are as follows:

Bt Cotton MECH 162 with BIPM Package

Non Bt Cotton MECH 162 with BIPM Package

Bt Cotton MECH 162 with Existing Farmers Practices

Non Bt Cotton MECH 162 with Existing Farmers Practice

The number of bollworms (H. armigera and E. vittella) were counted at 10 locations by selecting randomly five plants in each location (200 m²/loction) at 15 days interval starting from 15 DAS. The percent damage to fruiting bodies was recorded at 10 locations by selecting randomly five plants in each location at 15 days interval. The locule and inter locule damage were recorded at the time of harvest. In case of pink bollworm larval counts per ten bolls were taken. The observations were continued up to 150 DAS. The observations on sucking pests and natural enemies were recorded from 15 DAS onwards and continued up to 120 DAS. The data were analysed as described by Gomez and Gomez (1984).

RESULTS AND DISCUSSION

The major reason for the interest on Bt cotton in India is attributed to the skewed quantum of insecticide used on the cotton, particularly against H. armigera which is considered as the national pest which can lead to potential of 60-80% yield loss and its developed resistance to almost all group of insecticides. Transgenic crops are the important component of integrated pest management (Yuan et al., 1999). The performance of MECH 162 Bt and non Bt hybrids in the BIPM and FPP modules were investigated.

The incidence of sucking pests in different modules was in the decreasing order of FPP MECH 162 Bt > BIPM MECH 162 Bt > BIPM MECH 162 N Bt > FPP MECH 162 N Bt (Table 1).

Table 1:	Incidence of sucking pest population in different modules at different locations
*Mean of ten observations, *Figures in parenthesis are √x+1 transformed values, Means followed by different letter within column indicate significant differences (p = 0.05 DMRT)

The seed treatment with imidacloprid in FPP MECH 162 Bt reduced the sucking pest population, to a lower level than the other methods. The release of C. carnea at 45 DAS kept the sucking pest population incidence to a moderate level in BIPM modules.

Bhosle et al.(2004) studied the incidence of sucking pests in MECH 162, MECH 184, MECH 12 Bt and non Bt hybrids and they concluded that MECH 162 Bt and non Bt tolerant to sucking pest complex than the other hybrids. The release of C. carnea effectively reduced the sucking pests (Kulkarni et al., 2004) and bollworms (Anonymous et al., 1990). Hegde (1987) released C. carnea by larval brushing method and it reduced the insecticide application for sucking pests, bollworms and recorded higher yield of cotton.

The seed treatment with imidacloprid reduced the sucking pest population below economic threshold level up to 40 DAS (Mote et al., 1995; Patil et al., 2004 and Kannan et al., 2004) and was effective against leafhopper population up to 60 DAS (Dandale et al., 2001).

The incidence of natural enemies were more in BIPM modules than the FPP module plots (Table 3). Kulkarni et al. (2004) also recorded similar kind of results. Maximum activity of coccinellids and C. carnea was recorded in MECH 162 Bt BIPM and MECH 162 NBt BIPM modules. The decreased abundance of sucking pest population in FPP-MECH 162 Bt and the use of systemic insecticides in FPP MECH 162 N Bt might have reduced the incidence of their natural enemies. Kannan et al. (2004) and Satpute et al. (2002) concluded that the imidacloprid seed treatment attracted the coccinellids and lacewings. The lower incidence of sucking pest populations in the FPP MECH 162 Bt module, might have favoured the movement of these insects towards BIPM modules in this study.

Yuan et al. (1999) stated that the bollworm resistance in Bt cotton brings down the usage of insecticides by 60-80% and natural enemies population increases. In the present study, lower incidence of bollworm damage was noticed in MECH 162 Bt in both the modules than their isogenic lines. Similar trends were also noticed by several workers Yuan et al. (1999), Wu et al. (1999), Hegde (1987); Bhosle et al. (2004) and Kulkarni et al. (2004). Hedge et al. (2004) revealed that among the hybrids MECH 162 Bt (15.67) recorded lower boll damage than MECH 184 Bt (19.12) and MECH 12 Bt.

Bhosle et al. (2004) reported that the population of spotted bollworm (E. vittella) was significantly low in Bt cotton hybrids as compared to non Bt hybrids. They also recorded less population of H. armigera was noticed on MECH 162 Bt and MECH 184 Bt (0.87 larva/plant). Similarly in the present study, all the three locations the incidence spotted and american bollworms were very low in the Bt cotton hybrid (MECH 162) than the non Bt hybrid

The locule and intelocule damage was lower in Bt cotton MECH 162 than the non Bt in both the modules. The order of locule and interlocule damage was BIPM MECH 162 Bt > FPP MECH 162 Bt > BIPM MECH 162 N Bt > FPP MECH 162 N Bt. Similar observation also made by several researchers (Bhosle et al., 2004; Kulkarni et al., 2004; Hedge et al., 2004)

The pink bollworm P. gossypiella population was significantly low, (0 to 0.5) in the Bt cotton hybrids viz., RCH 2, RCH 20, RCH 144 and MECH 162 while it was 1.5 to 2.2 and 1.3 in the non Bt counterparts and check (Surulivelu et al., 2004). Hennebery and Jah (2000) reported that Bt cotton bolls (NuCOTN 33^B and DPL 5415) developing on plants 180 Days after Planting (DAP) were also toxic to pink bollworm larvae.

In the BIPM module, as the incidence of H. armigera was below Economic Threshold Level (ETL) throughout the crop period, HaNPV was not applied in the BIPM modules. The effectiveness of HaNPV to manage H. armigera in cotton ecosystem was already proved by Dhandapani et al. (1987), Sathiah (2001), Mastdi et al. (1995).

Table 2:	Incidence of bollworm damage in different modules

Table 3:	Incidence of natural enemies in different modules
*Mean of ten observations, *Figures in parenthesis are √x+1 transformed values, Means followed by different letter within column indicate significant differences (p = 0.05 DMRT)

Significant differences were noticed for yield of seed cotton among Bt and non Bt cotton (Elena, 2001). All the three seasons MECH 162 Bt in both modules recorded more seed cotton yield than the non Bt hybrids . The seed cotton yield in different modules was in the order of BIPM MECH 162 Bt > FPP MECH 162 Bt > BIPM MECH 162 N Bt > FPP MECH 162 N Bt (Table 2).

Kulkarni et al. (2004) revealed that Bt cotton MECH 162 in both BIPM and RPP recorded higher yield (11.00 and 13.00 g ha^-1) compared to non Bt (8.50 and 12.25 q ha^-1). Similar results recorded by Bambawale et al. (2004); Vennila et al. (2004); Hedge et al. (2004); Bhosle et al. (2004).

The compatibility of Bt cotton with the Integrated Pest Management (IPM) approaches was already recorded by Yuan et al. (1999). The results clearly indicated better performance of Bt cotton (MECH 162) in both the modules. BIPM approach reduces the insecticide usage. The IPM approach is essential for gaining higher advantage from Bt cotton as it takes care of varying pest situation. Even though, FPP proved better in reducing pests of cotton, it is advisable to opt for biorational approaches to manage pests of cotton for prolonged efficacy and better use of transgenic cultivars owing to their eco friendly nature.