Impact and Management of the Mexican Rice Borer (Lepidoptera: Crambidae) in Bioenergy Crop Agroecosystems

Abstract

The Mexican rice borer, Eoreuma loftini (Dyar) (Lepidoptera: Crambidae) is an invasive stem borer pest of sugarcane, rice, corn, and sorghum, and poses a threat to the production of dedicated bioenergy feedstocks in the U. S. Gulf Coast region. Studies were conducted to assess insect-plant interactions between E. loftini and bioenergy and conventional cultivars of sugarcane and sorghum, including yield response, oviposition preference, and host suitability. In addition, the efficacy of select cultural and biological control tactics to manage E. loftini in these crops was assessed. Bioenergy sugarcane (energycane) and sweet sorghum exhibited reduced E. loftini injury; however, these crops sustained greater losses in fresh stalk weight. Negative impacts to sucrose concentration from E. loftini injury were greatest in energycane, high-biomass sorghum, and sweet sorghum cultivars. Eoreuma loftini eggs per plant and eggs per oviposition event were greater on mature plants than immature plants. On a crop type basis, sweet sorghum was preferred over sugarcane and high-biomass sorghum when measuring eggs per plant. The mortality-survival ratio during the neonatal stage was greater in immature sugarcane cultivar HoCP 85-845 and high-biomass cultivar ES 5200. The percentage of bored internodes increased with higher nitrogen (N) rates. Yields indicated that N rate was positively associated with increases in stalk weight and ethanol productivity, but not sucrose concentration. Because higher N rates were associated with increased yields, our data suggest that increases in yield from additional N outweigh decreases from additional E. loftini injury. Populations of S. invicta reduced percent relative survival of E. loftini by 0.1% per increase unit increase of S. invicta; however, reductions in the percentage of bored internodes and adult emergence holes were not detected. Reductions in E. loftini injury from S. invicta were not detected in transects of johnsongrass. This research showed that select cultivars of bioenergy sugarcane and sorghum can be more resistant than conventional sugarcane and sorghum, demonstrating their compatibility in the Gulf Coast region. Because bioenergy crops are less tolerant to E. loftini in some instances, proper management practices should be continued, including judicial fertilization and conservation of natural enemies.