Dispersal of Trichogramma brassicae in tomato field

Abstract

A study was carried out to map dispersal of Trichogramma brassicae Bezd. on tomato in a 0.5 ha field. First, 1, 5, 10, 15, 20 and 25 meter distances from the central point of the field were marked in form of squares. On each square, 8 points were selected and a wooden stake of 1.5 m length was vertically secured into the soil at each point equal to plant height and bearing a yellow sticky trap (YST, 10 × 20 cm) on the top. Moreover, three egg batches each containing ~200 fresh Sitotroga cerealella Oliv.eggs on cardboards(SEC) were stapled on top leaf of three plants around the wooden stake arranged in a 0.75 m arch. Evaluation was done two days before and 2, 4, 6 and 8 days after a release of 50000 newly emerged T. brassicae (~1:1 Male:Famale) from the central point. The number of T. brassicae trapped by YST, and number of parasitised eggs on SEC were counted under a stereomicroscope and noted down. The coefficient of fitting YST data to the model (R2) for all 4 sampling dates was as high as 86%. The average diffusion coefficient was equal to 16.89 m2/day for four times sampling. In general, the distance encompassing 98% of trapped T. brassicae predicted by the model was up to maximum 29.9 m from the central point 8 days after the release. The mean percent parasitism was 44.7, 5.5, 5 and 0.9 per SEC during 2, 4, 6 and 8 days after release, respectively. It is concluded that, the farther the distance from the releasing point and the longer the time elapsed after release, the less number of wasps were recaptured. Therefore, multiple releasing points are required to achieve even distribution and enough population of parasitoids in the field.

Keywords

• biological control
• helicoverpa armigera
• augmentative release
• diffusion model