Characterization of Resistance to the Mexican Rice Borer (Lepidoptera: Crambidae) among Sugarcane Cultivars

SIMPLE SUMMARY: The Mexican rice borer, Eoreuma loftini, is one of the most important insect pests of sugarcane in the US. Management strategies that are environmentally friendly and economically profitable are needed to mitigate the pest’s impact. Cultivar resistance can become a key management strategy for Mexican rice borer control in sugarcane because it is inexpensive and easy for sugarcane growers to implement. Resistance is compatible with almost all other management strategies and minimizes further input costs incurred by the grower. However, the mechanisms of resistance are not completely understood. Elucidating which mechanisms and traits confer resistance can help sugarcane breeding programs increase the resistance level of future cultivar releases. We found that the currently grown commercial cultivars L 01-299 and HoCP 85-845 had the least amount of borer-related injury, while L 12-201 and HoCP 00-950 had the greatest level of injury. These differences appear to be related to the ability of recently hatched larvae to establish feeding rather than female preference to lay eggs on specific cultivars. Further work is needed to determine the influence of environmental factors on resistance expression and identify plant characteristics that are responsible for Mexican rice borer resistance. ABSTRACT: Cultivar resistance is an essential management strategy for the Mexican rice borer, Eoreuma loftini (Dyar), in sugarcane in the USA, but resistance mechanisms are poorly understood. Resistance was evaluated among Louisiana’s (USA) commercial sugarcane cultivars and experimental clones through field screenings, greenhouse trials, and a diet incorporation assay. Cultivars L 01-299 and HoCP 85-845 had the lowest borer injury levels, while HoCP 00-950 and L 12-201 were among the most heavily injured in field and greenhouse trials. The variability of results between the two field trials suggests that a genotype × environment interaction might affect the expression of resistance. Oviposition did not differ among evaluated cultivars in the greenhouse choice study. Results from the no-choice experiment showed that neonatal establishment differed among cultivars by up to 3-fold. In a diet incorporation assay, all cultivars reduced larval weight up to 86.5% and increased days to pupation by 1.8-fold relative to the diet-only control. Collectively, these results suggest that Louisiana’s sugarcane breeding germplasm contains various resistance levels to E. loftini, emphasizing the importance of screening cultivars before they are released to growers. Future studies should try to determine the influence of environmental factors on resistance expression.