Mechanisms of resistance to southern chinch bug, Blissus insularis Barber (Hemiptera: Blissidae), in St. Augustinegrass

St. Augustinegrass, Stenotaphrum secundatum (Walt.) Kuntze, is the most commonly grown lawn grass in Florida. The southern chinch bug (SCB), Blissus insularis Barber (Hemiptera: Blissidae), is the most serious insect pest of St. Augustinegrass. Host plant resistance has long been one of most successful management tools to control the SCB. Resistance to SCB has been identified in the St. Augustinegrass lines 'Floratam', 'FX-10' and 'NUF-76'. Floratam was once resistant but is now susceptible. This research investigated the mechanisms of SCB resistance in FX-10 and NUF-76. Choice and no-choice tests and ovipositional and developmental studies indetified strong antixenosis in FX-10 and NUF-76 and antibiosis in NUF-76. FX-10 and NUF-76 had significantly higher peroxidase activity and NUF-76 had significantly higher polyphenol oxidase activity 5 and 8 d after infestation compared to uninfested controls. FX-10 had significantly higher lipoxygenase activity 3, 5 and 8 d after infestation compared to uninfested controls. Native gels stained for peroxidase indicated that some isozymes in FX-10 and NUF-76 were induced 5 and 8 d after infestation. Electrical penetration graph studies showed that the SCB made more frequent probes, spent longer time on pathway related activities on FX-10 and NUF-76, compared to the susceptible Floratam and Palmetto. Significantly higher number of salivary sheaths was observed in the outermost leaf sheath in FX-10 and NUF-76. The total lignin content of the axillary shoot and the thickness of the epidermal layer in SCB resistant and susceptible St. Augustinegrasses did not differ significantly. TEM studies on the leaf sheath showed scelerenchyma cells with thicker cell walls in NUF-76 and FX-10 than in Floratam and Palmetto suggesting that the sclerenchyma cells around the vascular bundle in FX-10 and NUF-76 could serve as an impediment to the SCB stylet penetration. From this research, I conclude that the strong antixenosis found in FX-10 and NUF-76 and antibiosis in NUF-76 could be due to a combination of induction of oxidative enzymes, thicker sclerenchyma cells around the vascular bundle and possible presence of feeding deterrents or toxins in phloem sap or sieve tube blocking mechanisms.