This study aimed to investigate the effects of Bacillus thuringiensis on Liriomyza trifolii (Burgess) (Dipetera: Agromyzidae). L. trifolii is an important pest in vegetable growing areas in Şanliurfa, Turkey. Field trials were carried out in the experimental field of Faculty of Agriculture in Harran University through the July to November in 2005, employing randomized complete block design with three replicates. Adults of L. trifolii were obtained from laboratory culture and 5 ♀ ♀ and 5 ♂ ♂ and adults of L. trifolii were inoculated each plots at the first week of the production period. B. thrungiensis Berliner was applied at a concentration of 60×106/mg Bacillius thrungiensis spore. B. thrungiensis was applied at the recommended rate of 75 g/100 L water. Application dates were set when the pest density reached a level of 4-5 larvae/leaf which are economic threshold. The application of B. thrungiensis was done the 3rd week and application continued once a 15 day throughout the 9th week production periods, because the pest density reduced a level of 4-5 larvae/leaf the last 5 weeks. Total application of B. thrungiensis was 4 times throughout the bean production period. The leaves were sampled weekly from B. thuringiensis treated and non-treated plots and kept in laboratory under observation to compare the number of emerging leaf miner adults and their parasitoid species. B. thuringiensis reduced leaf miners as compared to non-treated plots. On the other hand, the highest yield was recorded with the B. thuringiensis treated plots. The results indicate that, B. thuringiensis should be treated only once every 2-3 weeks for effective control of L. trifolii. The percentage of parasitization in the B. thuringiensis non-treated plots were higher than B. thuringiensis treated plots and the percentage of parasitization were 59.14 and 50.69% respectively. © 2006 Asian Network for Scientific Information.