Onion ( Allium cepa L.) is one of the native plants of Iran . This valuable crop is damaged by many kinds of pests during its growth period in the field and also in the storage. One of the important pests of onion is Thrips tabaci Lind. which is a very polyphagous species and causes high crop damage and yield loss. Several sustainable methods of control have been developed in recent years for reducing thrips damage in field vegetable crops. As a result, more selective insecticides (insect growth regulators) are now being introduced into crop production. This has helped to overcome some of the problems that occur when pest insects develop resistance to certain insecticides. One sustainable method of control is intercropping in which two or more species of plants which are hosts of a pest are intercropped to lower the damage made by the pest or to trap the pest and eliminate it. In order to study the application of insect growth regulators (Pyriproxyfen and Buprofezin) for controlling onion thrips ( Thrips tabaci Lind.) in intercropping of onion and tobacco during two agriculture years, the seeds were planted in plots as a split split plot experiment in a randomized block design with three replications. The plots were onion monocro and onion-tobacco intercrop. The main treatments were profenofos, buprofezin, pyriproxyfen, buprofezin+pyriproxyfen and water (control) and secondary treatment were Ghom and Dorcheh onion cultivars. Thrips population and percentage of injury on plants, degree of top leef curling, fresh and dry weight, plant height and bulbing ratio of plants were determined. Also, after harvest, the yield and the effect of spraying on the cultivars were determind. During the second year of study the effect of insect growth regulator, on the abundance of pest and injury to onion plants were studied. The results showed that population of thrips on different threatments, were significantly different. In the first year, buprofezin+pyriproxyfen treatment showed minimum population density of thrips. But in the second year pyriproxyfen treatment showed minimum population density of thrips. Threatments showed no significant difference on the other traits. Significant different abserved between traits of cultivars. Dorcheh showed maximum population density of thrips and percentage of injury but Ghom had minimum of these characters. Dorcheh had minimum of fresh and dry weight, plant height and yield. Ghom showed the maximum fresh and dry weight plant height and yield. The large differences observed for most traits are due to high genetic diversity among cultivars. Comparison of traits in different times of samplingrernce for population
