Technical Abstract: The tarnished plant bug is an economically important pest. Control of the insect mainly relies on chemical insecticides. Heavy selection pressure prompted resistance development in the target insect. This study was conducted to survey dose response to Orthene in different plant bug populations collected once a month from May to September in 2011 in Delta. Most of the field populations were collected from pigweeds around edges of cotton or soybean fields. Approximately 25 bugs were used as a replication and 3 replications were used for each population. For spraying treatment with Orthene, the bugs along with 4 green bean pods were placed in a plastic container (diameter[D]×hight[H]: 10.5×7cm). A 7-cm(D) hole was cut at the bottom of the container and covered a fine mesh cloth. A 9-cm(D) hole was cut on the lid and covered with a fine net cloth (10 grids/cm). Orthene 90WP was dissolved in d-H2O to a concentration of 80 mg/L, which is a LC50 value against the standard laboratory susceptible colony. Exactly 500 µl of Orthene solution was delivered into the container using a modified Potter Spray Tower. The sprayer was set at 7.5 psi and spray distance of 30.5 cm to ensure a uniform deposition of the Orthene mist on the inner surface of the container, green beans, and bugs. Bioassay results showed that different populations had different susceptibilities. Survival rates ranged from 25-74% in May, 24-59% in June, 7-70% in July, 10-95% in August, and 10-81% in September. In addition to bioassays, esterase and glutathione S-transferase activities and gene regulation were examined. Analysis of 6,688 genes using microarray revealed 635 differentially expressed genes (=2-fold) in resistant strain. Ninety-nine up-regulated and 134 down-regulated genes were annotated. Eleven esterase, 4 cytochrome P450, and one glutathione S-transferase genes were significantly up-regulated, and no such genes were down-regulated in the resistant insects.