Tarnished plant bug, Lygus lineolaris (Palisot de Beauvois), populations were collected from field locations in the Mississippi River Delta of Arkansas, Louisiana, and Mississippi. Third-instar F₁ nymphs from each field location, in addition to a laboratory colony, were screened for susceptibility to novaluron. Both a glass vial bioassay and a diet-incorporated bioassay used dose-response regression lines to calculate LC₅₀ and LC₉₀ values for novaluron. Mean LC_50s for glass vial bioassays ranged from 44.70 ± 3.58 to 66.54 ± 4.19 µg/vial, while mean LC_50s for diet-incorporated bioassays ranged from 12.10 ± 0.77 to 17.63 ± 2.42 µg/200 ml of artificial diet. A comparison of LC₅₀ values from the same field population screened using both bioassay methods failed to show a relationship. LC₅₀ values from field locations were compared with a historically susceptible population from Crossett, AR. Results indicated that considerable variability in susceptibility to novaluron exists within field populations of tarnished plant bugs across the Delta, including some locations with lower LC₅₀ values than a historically susceptible population.