Estimating yield loss from the Mexican rice borer, Eoreuma loftini, in conventional and bioenergy crops

An experiment was conducted in 2012 and 2013 at the Texas A&M AgriLIFE Research and Extension Center at Beaumont, Texas to evaluate yield loss from the Mexican rice borer (MRB), Eoreuma loftini (Dyar), in conventional and bioenergy varieties of sugarcane and sorghum.  Varieties included one MRB-susceptible sugarcane (HoCP 04-838), one MRB-resistant sugarcane (HoCP 85-845), two energycanes (L 79-1002, HoCP 02-113), two high-biomass sorghums (ES 5200, ES 5140), and one sweet sorghum (M81E).  Varieties were subjected to four MRB infestation levels, ranging from suppressed (with insecticides) to highly enhanced.  Infestations were enhanced by clipping egg masses to plant leaves.  The impact of MRB infestation level on two yield parameters, wet weight and theoretical ethanol output, was compared across all varieties.  Results showed an increase in MRB-related injury at higher infestation levels. Under highly-enhanced infestations, the percentage of bored internodes ranged from 9.1–26.8%, with varieties of energycane and sweet sorghum sustaining the lowest injury levels.  In terms of yield, higher infestations of MRB were associated with reduced stalk weight and theoretical ethanol output across all varieties.  Under highly-enhanced infestations, decreases in ethanol production ranged from 12–42% when compared to suppressed infestations.  For both conventional and bioenergy varieties, maximum ethanol productivity was achieved under suppressed infestations.  This is the first documentation of yield loss attributed to the MRB in bioenergy crops.