The southern chinch bug, Blissus insularis Barber (Hemiptera: Blissidae), is the most important insect pest of St. Augustinegrass, Stenotaphrum secundatum (Walt.) Kuntze, in Florida and other Gulf Coast states. Resistance to southern chinch bug was identified previously in St. Augustinegrass lines ‘FX-10’ and NUF-76. Choice and no-choice tests and ovipositional and developmental studies were conducted to determine the categories of resistance in FX-10 and NUF-76 to southern chinch bug. When adult chinch bugs had a choice among attached stolons of three susceptible lines (‘Floratam’, ‘Bitter Blue’, and ‘Palmetto’) and the two resistant lines, chinch bugs were found significantly more often over a 5-d period on the susceptible lines. This result indicates the presence of antixenosis in the resistant lines FX-10 and NUF-76. In a no-choice study, chinch bugs produced less than half as many excretory spots on FX-10 as on the susceptible lines. Significantly fewer excretory spots produced by chinch bugs confined on NUF-76 accumulated by days 3 and 5 after release; however, on the first 2 d, the accumulative number of excretory spots was not significantly less than that found on susceptible lines. The no-choice study confirmed a high level of antixenosis in FX-10, a moderate level of antixenosis in NUF-76, and possible antibiosis in NUF-76. Ovipositional and developmental studies were conducted using only Floratam (a widely planted cultivar that was formerly resistant to B. insularis) and the two resistant lines. Adults released on Floratam produced 11 and 5 times more eggs and 18 and 9 times more offspring than adults on FX-10 and NUF-76, respectively. Plant anatomical and biochemical studies are required to investigate the exact cause of antixenosis in FX-10 and NUF-76 and possible antibiosis in NUF-76.