In recent years, a total area of over 32 million ha in agriculture and forestry in the world has been treated annually with Trichogramma spp for controlling insect pests. In the world wide use of Trichogramma spp, the former USSR ranked first, followed by China and Mexico. Extensive utilization of this parasitoid was developed for rice, corn, sugarcane, cotton, vegetable and pine. The selection of suitable species, quality parasitoids, reasonable release rate per hectare, climate during release and release methods are the factors that determine the efficiency of Trichogramma spp. Therefore, investigations were carried out in the biocontrol laboratory at North Carolina State University, Raleigh, USA, to examine costs (negative fitness effect as well as beneficial effects) for heat resistance acclimation in an egg parasitoid, T. exiguum by exposing of immature stages to 40o C for different periods. The focus of the study was on acclimation across life-cycle stages rather than short term hardening of adults. Three questions ware considered. Firstly, can adult resistance to a high temperature shock, be increased by pre-pupal acclimation and / or by pupal acclimation in T. exiguum?. Secondly, are there other benefits of acclimation?. Thirdly are treatments that increase resistance associated with costs in terms of decreased parasitism or decreased longevity and can these costs be overcome by modifying acclimation treatments. So for, there has been little work in Trichogramma spp even through these parasitoids form an important component of IPM strategy in many countries and despite the fact that high temperature decrease Trichogramma spp., parasitism rate. The findings indicates that acclimation can occur without costs in T. exiguum and suggest a general phenotypic approach for separating acclimation costs from other fitness costs by sub - lethal exposures.