Biological control plays an important role in integrated plant protection. Beneficial insects are rather important in modern biological control practice for reducing pests’ density. The Institute of Genetics, Physiology and the Plant Protection of ASM, Chisinau, Moldova conducts fundamental and applied research with Trichogramma to settle technical issues, improve entomophage’s quality and effectiveness in plant protection to obtain ecologically safe products. To improve parasitoid quality and efficacy, it is necessary to select the right species best adapted to natural conditions of certain zones with certain species. In mass rearing of Trichogramma, the numerical density of the initial colonies grows by tents, even hundreds of times leading to a depression the number of inherited crossings and thus leading to sexual deregulation of the population, and to a lowering of the quality of Trichogramma. Such factor as interspecific competition becomes particularly important at Trichogramma mass rearing and releasing into the field. At relative trophic specialization of Trichogramma competitive capacity impacts its efficacy. During the rearing of the laboratory host, biological indices have been determined for T. evanescens (prolificacy, hatching, females’ rate) reared on these eggs. Experiments carried under laboratory and field conditions. Experiments have been made in three climatic chambers SKP-1 at average daily temperatures of 15°C, 20°C, 25°C and relative humidity of 50%, 65%, 80%, at photoperiod lasting for 16 hours. Experiments have been effectuated according to Box-3 plan. Collecting, identification, storage and accumulation of Trichogramma species were done using (according to) (DIURICI, 2008). Five trial variants in five repetitions have been conducted in the Institute of Genetics, Physiology and the Plant Protection Institute of ASM Moldovan Academy of Sciences, using various reports on Trichogramma species under laboratory and field conditions: T. evanescens – 100%; T. pintoi – 100%; T. evanescens+T. pintoi – 50% +50% T. evanescens+T. pintoi–10% +90%; T. evanescens+T. pintoi–90% +10% Laboratory experiments results have demonstrated that during 4 generations of Trichogramma development T. evanescens Westw. has been gradually substituted by T. pintoi Voeg. When share ratio of T. evanescens and T. pintoi equals to 1:1 passed through Angoumois grain moth eggs (Sitotroga cerealella Ol.) after the fourth generation it has been noticed that at T=15°C combined with different humidity’s, T. pintoi share has constituted from 68.3 to 83.95% and T. evanescens share – 16.1 to 31.7%; at T = 20°C these parameters have ranged, respectively, from 76.0-95.0% and 5.0 to 24.0%, while at T=25°C – they ranged from 76.1 to 100% and from 0 to 23. 9%. When shares of T. evanescens and T. pintoi have equaled respectively to 9:1 substitution rate of T. evanescens has been more reduced. However at T-15°C in mixed batch there remained from 42.9 to 45.0% of T. evanescens at T=20°C, respectively, from 38.9 to 45.0%, at T=25°C – from 31.5 to 38.35%. At the end of all experiment variants no T. evanescens have been found, while at T=25°C similar situation has been observed for the III-rd generation. The mechanism of substituting one species by the other has been explained by different response of T. evanescens and T. pintoi on temperature and humidity regimes at mass rearing. As a result of the laboratory experiments, it has been established that along the 4 development generations of mixed T. evanescens Westw., T. pintoi Voeg. gradual substitution of T. evanescens by T. pintoi occurs. The mechanism of interspecific competition on grain moth eggs was established. In the field of cereal, technical and vegetable crops, T. evanescens is dominant specie (up to 95-99%). T. pintoi represents a laboratory population, which’s preferred host is Siotroga cerealella Ol. In the presence of the two species of Trichogramma in the biotope, their quantitative ratio depends on the specific conditions of climate and resource of preferred host’s egg. Biological indices for T. pintoi are higher than ones of T. evanescens. Therefore, in the laboratory conditions we substitute T. evanescens by T. pintoi, but in the field it’s opposite. After the first release of mixtures of T. evanescens and T. pintoi (50:50%), share in percentage has constituted 91.05% for T. evanescens and 8.95% for T. pintoi. After the second release respective shares have been as follows – 94.5% and 5.5%. After the first release of mixture of T. evanescens and T. pintoi (10:90%) egg lying of the cabbage moth have been parasitized at the level of 85.6% by T. evanescens and at the level of 14.4% by T. pintoi, after the second release – respectively – 88.8 and 11.2%. After the first and second releases of T. evanescens and T. pintoi mixtures (90:10%) analyses have shown that it is T. evanescens that actually controlled the pest in the field while T. pintoi has not been found. As a result of the laboratory experiments, it has been established that along the 4 development generations of mixed Trichogramma, gradual substitution of T. evanescens by T. pintoi occurs. It has been established that under natural conditions species competition has been lower. To the above said contribute fluctuations of temperature and humidity, localization of host eggs in time and space, as well as more intensive accumulation of species that are not specific for this biocenosis (for example T. pintoi). However, if further Trichogramma release is not made, the dominant species is restored. In case of presence of two species in the biotope quantitative share will depend on specific climatic conditions and the number of preferable host individuals.