Abstract

'Floratam' St. Augustinegrass [Stenotaphrum secundatum (Walt.) Kuntze] has been widely used in lawns because of its resistance to the southern chinch bug (Blissus insularis Barber).  The southern chinch bug adapted genetically to Floratam and seriously damaged this cultivar within 12 yr after release.  The Floratam- adapted southern chinch bug has been described as the polyploid damaging population (PDP), because polyploid germplasm had previously shown resistance.  This study examined polyploid germplasm for resistance to the PDP southern chinch bug.  Stenotaphrum clones were bioassayed by confining stolon cuttings with PDP southern chinch bugs from different regions.  Resistant clones were detected based on reduced southern chinch bug longevity, oviposition rate, and excrement production, compared with Floratam.   The most resistant clones were PI 365031, a pembagrass [S. dimidiatum (L.) Brongn.], and FX-2, FX-10 and FX-33 (intercrosses of polyploid S. secundatum from Africa).  They supported low PDP southern chinch bug oviposition (<5 eggs female^-1 wk^-1 and <25 eggs lifetime^-1).  Resistance of FX-33 was verified against PDP southern chinch bugs (representing laboratory colonies and field recollections) in mated pairs and congregations, and against southern chinch bugs that had received different prior food sources.  Both FX-33 and FX-10 typified the African polyploid St. Augustinegrass germplasm by having 2n = 30 chromosomes, bivalent pairing at metaphase I, good crossed seed setting and abundant laminar hairs.