Abstract
Cultivar resistance is a key management strategy for the stem borer complex (Lepidoptera: Crambidae) in Louisiana sugarcane, but mechanisms of resistance are not well understood. This research evaluated the potential mechanisms of cultivar resistance to Diatraea saccharalis and Eoreuma loftini among commercial sugarcane cultivars and experimental clones through a series of field screenings, greenhouse trials, and diet incorporation assays. The stem borer resistant standard HoCP 85-845 and cultivar L 01-299 were among the cultivars with the lowest borer injury levels in both field and greenhouse trials. Cultivars HoCP 00-950, L 12-201, and HoCP 14-885 were among the most heavily injured in field trials. The variability of results from E. loftini field trials suggests that a genotype × environment effect might affect the resistance levels of cultivars. Rind hardness from field traits was associated with resistance to D. saccharalis in field trials. Differences in oviposition among cultivars in the greenhouse choice study were not detected, suggesting adult preference is not a key factor in resistance, and future studies should compare Louisiana’s cultivars to cultivars with known oviposition non-preference. Conversely, results from the no-choice greenhouse experiment revealed up to 9-fold differences were present among cultivars in neonate establishment for both stem borer species. For D. saccharalis in the laboratory experiment, lower larval weights and longer days to pupation were observed for resistant germplasm Ho 08-9003, but no significant effects were found among current commercial cultivars. In the E. loftini diet experiment, larval weight was reduced by 59.2–86.5% relative to the artificial diet control but did not differ among cultivars. These results suggest a range of resistance levels remains present in sugarcane breeding germplasm and highlight the importance of screening cultivars before commercial release. Future studies of stem borer resistance mechanisms should attempt to devise a measurement of leaf sheath tightness and pubescence.
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