Western flower thrips (Frankliniella occidentalis, WFT) is an important pest of sweet pepper in greenhouses in the Republic of Moldova. A greenhouse population of WFT on sweet peppers, which is difficult to control, has been studied. The high growth rate of the WFT population (333%) and its dominant position (56%) are largely dependent on ecological factors in greenhouses and the insecticides used. There is no interspecific competition between local thrips species and the invasive WFT due to the low abundance and species diversity of thrips. The prolonged and frequent use of insecticides without alternative control measures has resulted in 51.7±2.6%, 20.6±1.8% and 22.0±3.3% adults of the population being resistant to the active ingredients of the insecticides cypermethrin, thiamethoxam and abamectin, respectively. No resistance to spirotetramat has been detected in WFT larvae. The year-round cultivation of vegetable and ornamental crops in Ecoplantera's greenhouses contributes to the preservation of this pest population. To ensure sustainable control of WFT in greenhouses, it is recommended to apply an integrated pest management (IPM) approach, with the obligatory use of entomophages and entomopathogens.