The experiment was conducted in the laboratory and experimental field of Entomology Division, BARI, Gazipur during 2008-09 Rabi season.
Treatments: Two species of egg parasitoids Trichogramma chilonis and T. evanescens and one larval parasitoid Bracon hebetor were used in this experiment. Treatments were Trichogramma chilonis @ 1g/ha, T. evanescens @ 1g/ha, Bracon hebetor @ 1200/ha, Trichogramma chilonis @ 1g/ha + Bracon hebetor @ 1200/ha, T. evanescens @ 1g/ha + Bracon hebetor @ 1200/ha and untreated control
Design and layout: The experiment was laid out in randomized complete block design (RCBD) with three replications.
Treatment application: Two species of egg parasitoids Trichogramma chilonis and T. evanescences along with one larval parasitoid, Bracon hebetor were used in this experiment. In the field, each micro plot was covered by mosquito net (1.5m x 2m x 1m) cage having eight tomato plants. The mosquito net was provided at seedling stage and left upto 75 days after transplanting. When tomato plant started flowering, two pairs of adult Helicoverpa armigera were released in each micro plot. Two species of Trichogramma were released four days after adult host release. Bracon hebetor was released eight days after adult H. armigera release according to the treatment. Only T. chilonis was released as a treatment and only T. evanescens was released in another treatment. Only Bracon hebetor was released eight days after adult H. armigera release as one of the treatment whereas T. chilonis as well as B. hebetor were released as combined treatment. On the other hand, T. evanescens and B. hebetor were released as another combined treatment. Only 2 pair of adults H. armigera were released in the untreated control plot. Parasitoids were released weekly up to seven times during the entire study period
Collection and calculation of data: Procedure for data collection and calculation of percent fruit infestation by number in- by number (at in situ also) and weight at harvest, yield at each harvest were stated below:
Percent fruit infestations by number at in-situ condition:
Data on fruit infestation by number (formula given below) were recorded at 7 days interval.
Number of infested fruits
% Fruit infestation by number = x 100
Total number of fruits
Per cent fruit infestation by number:
The percent fruit infestation was calculated using the following formula:
Number of infested fruits
% Fruit infestation by number = x 100
Total number of fruits
Per cent fruit infestation by weight: The percent fruit infestation was calculated using the following formula:
Weight of infested fruits
% Fruit infestation by weight = x 100
Weight of total fruits
Marginal Benefit cost ratio: Marginal benefit cost ratio was calculated by using following formula:
Benefit on control
Marginal BCR = --------------------------
Cost of treatment