Molecular Based Strategy for Assessing Dispersal of Trichogramma spp. ( Hymenoptera: Trichogrammatidae) After Release in Organic Apple Orchards.

Challenging pest problems resulting in huge crop losses and a reduction in external quality is a major constraint to increased production of organic apples worldwide. Trichogramma is an effective tool in the biocontrol of insect pests of apple because it does not cause any harm to the vegetation, yet it destroys its hosts before plants can be damaged by parasitizing their eggs. Most approaches targeted towards assessing the release of Trichogramma often neglect existing local population. They have focused more on measuring degree or impact of parasitism rather than evaluating the efficacy of dispersed parasitoids. This study demonstrates successful application of molecular tools utilizing ITS2 region of the ribosomal DNA to assess the identity of Trichogramma individuals in a population. Parasitized eggs of codling moth Cydia pomonella (Lepidoptera: Tortricidae) were collected from 4 plots of apple tree in Germany after augmentative release. Parasitoid wasps that emerged from the eggs during 3 field trials were identified based on random amplified polymorphic DNA (RAPD) and restriction fragment length polymorphism (RFLP) patterns. Results from the third trial showed that 29.3% of parasitism observed was from indigenous population of T. evanescence while the released strains of T. cacoeciae and T. brassicae constituted 38.2% and 32.5% respectively. This molecular approach involving an analysis of indigenous population is useful in making comparisons of the efficiency of local population with that of other strains or species.