Dispersal behavior of Trichogramma brassicae in rice field

Dispersal of Trichogramma brassicae Bezd. was studied in 2 rice fields by a single release of 50000 adult wasps from a central point and recapturing them using yellow sticky traps and egg cards of Sitotroga cerealella (Oliv.) Results revealed that in rice field 1, dispersal coefficients were 3.04 and 1.07 m2/day at 1st and 2nd sampling turns. However, it reached to a level of 11.28 m2/day at 3rd sampling turn. In contrast, T. brassicae dispersed with a speed of 3.93 m2/dayat 1st sampling turn and had the highest dispersal coefficient (29.76 m2/day) at 3rd sampling turn in rice field 2. Similarly, the distances that encompassed 98% recaptured T. brassicae was highest in field 2 (53.45 m) compared with that in field 1 (15.11 m) at 3rd sampling turn. Number of wasps remained in fields 1 and 2 were recorded as 630.67 and 272.18 individuals, respectively, for total sampling turns. Moreover, the highest parasitism rates (64.75 and 91 mean parasitized eggs/card in fields 1 and 2, respectively) were observed at 1 meter distance from release point at first sampling turn and it decreased with time and distance elevation. It is concluded that more release points of T. brassicae per rice field is required to achieve universal dispersal in successful rice stem borer biocontrol. It needs innovation in packing and release method of the wasp.