A Relative Resistance Ratio for Evaluation of Mexican Rice Borer (Lepidoptera: Crambidae) Susceptibility Among Sugarcane Cultivars

Resistance to Diatraea (Lepidoptera: Crambidae) stem borers in sugarcane is independent of species

Evaluation of host-plant resistance on sugarcane to the sugarcane stem borers of Diatraea spp. is normally conducted in Colombia under field conditions, where environmental variations make the study of the insect-plant relationships difficult. Additionally, several species (i.e., D. saccharalis, D. indigenella, D. tabernella, and D. busckella), which are predominant in Colombia, can overlap in their distribution, raising the question of whether different varieties have the same responses to different pest species. The present study conducted evaluations of host-plant resistance under screen house conditions using two contrasting varieties (CC 93-3895, resistant, and CC 93-3826, susceptible) that were infested with the above-mentioned borer species. Observations of pest injury were conducted on internodes, leaves, and spindles. Survival and size (body mass) of the individuals recovered were analyzed and a Damage Survival Ratio (DSR) was proposed. The resistant CC 93-3895 exhibited less stalk injury, less emergence holes on internodes, and lower DSR; additionally, recovery of pest individuals was lower in comparison with CC 93-3826, independent of the borer species. Insect-plant interactions are discussed, as no previous information was available for three of the species tested (i.e., D. tabernella, D. indigenella, and D. busckella). This screen house protocol is proposed to characterize host-plant resistance among several cultivars from the Colombian sugarcane germplasm bank, using CC 93-3826 and CC 93-3895 as contrasting controls and D. saccharalis as the species model.

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

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.

Resistance to the Sugarcane Borer (Lepidoptera: Crambidae) in Louisiana Sugarcane Cultivars

Cultivar resistance is a key management strategy for the sugarcane borer, Diatraea saccharalis (F.), the primary pest in Louisiana sugarcane, but mechanisms of resistance are not well understood. This research evaluated the potential mechanisms of cultivar resistance to D. saccharalis among commercially produced sugarcane cultivars and experimental lines through three field screenings, two greenhouse experiments, and one diet incorporation assay. The resistant standards HoCP 85-845, HoCP 04-838, and L 01-299 were among the cultivars with the lowest D. saccharalis injury levels in both field and greenhouse trials. Cultivars HoCP 00-950 and L 12-201 were among the most heavily injured in both trials. Differences in oviposition among cultivars in the greenhouse choice study were not detected, suggesting adult preference is not a key factor in resistance. This was also supported by the no-choice greenhouse experiment in which up to 9-fold differences in neonate establishment among cultivars were detected. Larval injury among cultivars in greenhouse experiments was consistent with field studies suggesting traits that affect neonate establishment (e.g., rind hardness) help to confer resistance in the field. In the diet incorporation assay, lower larval weights and longer time to pupation were observed on resistant cultivar Ho 08-9003, but no differences were found among current commercial cultivars. Continuous evaluation of cultivar resistance to D. saccharalis is important in developing effective integrated pest management strategies for this pest. More research into plant characteristics (e.g., leaf sheath tightness and pubescence) associated with resistance is needed.

Effects of Patch Size, Fragmentation, and Invasive Species on Plant and Lepidoptera Communities in Southern Texas

Habitat loss, fragmentation, and invasive species are major threats to biodiversity. In the Lower Rio Grande Valley (LRGV) of southern Texas, a conservation hotspot, few studies have examined how land use change and biotic disturbance influence biodiversity, particularly among Lepidoptera. We surveyed 24 habitat fragments on private lands in the LRGV and examined how patch size, edge to interior ratio (EIR), prevalence of invasive, exotic, and pest (IEP) plant species, and other environmental factors influenced plant and Lepidoptera communities within four habitat classes. Biotic disturbance was widespread and intense. IEP plants represented three of the four most common species in all but one habitat class; yet, classes largely had distinctive plant and Lepidoptera communities. Larger habitat patches had lower IEP prevalence but also lower plant richness and lower Lepidoptera richness and abundance. Conversely, patches with higher EIRs had greater IEP prevalence, plant richness, and Lepidoptera richness and abundance. IEP prevalence was negatively related to plant diversity and positively related to woody dominance, blooming plant abundance, and, surprisingly, both plant cover and richness. However, plant richness, abundance, and diversity were higher where a greater proportion of the plants were native. Lepidoptera diversity increased with plant cover, and Lepidoptera richness and abundance increased with plant richness. More individual Lepidoptera species were influenced by habitat attributes than by availability of resources such as host plants or nectar sources. Our results illustrate extensive landscape alteration and biotic disturbance and suggest that most regional habitats are at early successional stages and populated by a novel species pool heavy in IEP species; these factors must be considered together to develop effective and realistic management plans for the LRGV.

Successful Integrated Pest Management Minimizes the Economic Impact of Diatraea saccharalis (Lepidoptera: Crambidae) on the Louisiana Sugarcane Industry

The sugarcane borer, Diatraea saccharalis (F.), is the primary pest of sugarcane, Saccharum spp., in Louisiana. Recent evidence suggests an integrated pest management (IPM) program has reduced the pest's impact, but the success of this program has not been assessed across the industry. The level of D. saccharalis injury present at harvest was recorded from 388 billet samples from five sugar mills from 2017 to 2019. These results were used to estimate direct and indirect revenue losses from D. saccharalis on the Louisiana sugarcane industry. Insecticide use records were used to estimate control costs and determine total economic impact. The mean percentage of bored internodes was 1.1, 0.3, and 1.7% for 2017, 2018, and 2019, respectively. Direct losses from reduced sugar yield averaged US$4.6 million across years. Indirect losses across years accounted for US$3.0 million and $463,000 for insecticidal control costs and reduced milling efficiency, respectively. The total economic impact of D. saccharalis averaged $8.0 million annually during the three-year study period. This study demonstrates the efficacy of pest management implementation in reducing D. saccharalis injury and highlights the value of IPM. Our findings provide new support for the emergence of D. saccharalis management in the Louisiana sugarcane industry as a modern IPM success story.

Population Trends of the Sugarcane Borer (Lepidoptera: Crambidae) in Louisiana Sugarcane

The sugarcane borer, Diatraea saccharalis (F.) (Lepidoptera: Crambidae), is the primary pest of sugarcane, Saccharum spp., in Louisiana. Spring populations are not considered economically damaging, but quantifying infestations can provide an indication of the spatial and temporal character of the damaging summer populations. Statewide surveys quantified the density of sugarcane tillers killed by D. saccharalis (deadhearts) from sugarcane fields across the state in spring from 2003 to 2020. Deadheart density varied greatly among years with a high of 1,318/ha in 2003 to a low of 0/ha in 2018. Linear regressions of the 3-yr rolling average showed declines in spring D. saccharalis populations and the percentage of acreage treated with insecticides over 17 yr. Weather factors including minimum winter temperatures and average spring temperatures were poor predictors of D. saccharalis populations. Only total precipitation in the month of April was positively correlated with numbers of deadhearts per hectare. Results suggest overwintering mortality is not a key factor influencing populations of the first generation of D. saccharalis in Louisiana. Total precipitation in the month of July was positively associated with percentage of treated acreage. Spring deadheart density was directly related to percentage of acreage treated with insecticides during the summer. Quantifying first-generation D. saccharalis populations by recording deadheart density can aid in predicting pest pressure later in the growing season.

West Indian Canefly (Hemiptera: Delphacidae): An Emerging Pest of Louisiana Sugarcane

The West Indian canefly, Saccharosydne saccharivora (Westwood) (Hemiptera: Delphacidae), is a sporadic pest of sugarcane in Louisiana which has recently emerged as a more consistent threat with outbreaks occurring in 2012, 2016, 2017, and 2019. Surveys of commercial fields in 2016 revealed that S. saccharivora infestations were present throughout Louisiana sugarcane and populations peaked in mid-June before declining. High minimum winter temperatures are generally associated with S. saccharivora outbreaks. Six insecticide evaluations demonstrated effective control with several insecticides including λ-cyhalothrin, flupyradifurone, acetamiprid, and imidacloprid. In five of the six insecticide trials, S. saccharivora infestations had substantially declined by 21 d after treatment. Effects of insecticidal control of S. saccharivora on sugar yields were detected in one of four small plot trials in which yield data were collected. Linear regression revealed S. saccharivora cumulative insect days in a grid sampling study were inversely associated with sugar yields. Results from these collective experiments suggest impacts on sugar yields are influenced by pest density and infestation duration. Differences were detected in numbers of S. saccharivora nymphs and adults as well as sooty mold coverage among commercial sugarcane cultivars with more than twofold increases in the most susceptible compared to resistant cultivars. The research presented herein documents the impact of S. saccharivora to Louisiana sugarcane and provides important ground work for developing effective pest management strategies. Future research efforts should aim to identify ecological factors influencing population dynamics, varietal preferences, and economic thresholds.

Effect of Sugarcane Cultivar and Foliar Insecticide Treatment on Infestations of the Invasive Sugarcane Thrips, Fulmekiola serrata (Thysanoptera: Thripidae), in Florida

Fulmekiola serrata (Kobus) was observed infesting sugarcane, Saccharum spp. hybrids, in the United States for the first time in January 2017 in Florida. Field studies were conducted to determine F. serrata infestation levels on popular sugarcane cultivars and to determine the efficacy of foliar insecticide treatments that could be used for management. Cultivar evaluations comparing six and five commercial cultivars representing >46% of the sugarcane production area in Florida were conducted in 2017 and 2018, respectively. Fulmekiola serrata infestation levels did not differ among cultivars in 2017. However, infestation levels on CP 00-1101 were greater than on CP 96-1252 grown on organic soils, and infestation levels on CP 96-1252 were greater than on CPCL 97-2730 grown on mineral soils in 2018. Three insecticide evaluations, two in 2017 and one in 2018, were conducted. The pyrethroid lambda-cyhalothrin, which is registered for use on sugarcane, was consistently associated with the greatest decreases in F. serrata infestation levels. The neonicotinoids imidacloprid and thiamethoxam, as well as the butenolide flupyradifurone, decreased infestation levels but to a lesser extent than did lambda-cyhalothrin. The spinosyn spinetoram was associated with the lowest decreases in F. serrata infestation levels. Our results supported short-term F. serrata management recommendations: Popular Florida sugarcane cultivars should be considered equally susceptible to F. serrata until additional evaluations are conducted and F. serrata outbreaks can be treated with lambda-cyhalothrin when infestations stress the crop beyond acceptable levels.

Interaction of Cultural, Biological, and Varietal Controls for Management of Stalk Borers in Louisiana Sugarcane

Diatraea saccharalis F is considered the most important pest of sugarcane in the United States. This article focuses on the history of pest management as it relates to the control of this stem borer in Louisiana sugarcane, and how control practices have become more in tune with integrated pest management paradigms. Various pest management strategies are employed against D. saccharalis and the interactions between each of these provide farmers with the tools needed to curb damaging infestations. However, the invasion of the Mexican rice borer, Eoreuma loftini (Dyar), and other confounding environmental factors have presented farmers, consultants, and researchers with new pest management challenges. We address these challenges and provide an overview of ongoing developments, particularly in the Louisiana sugarcane pest management program.

Mexican Rice Borer Control Tactics in United States Sugarcane

The invasive Mexican rice borer, Eoreuma loftini (Dyar), expanded its range from Mexico to South Texas in the early 1980s. By 2008 the pest had moved into sugarcane- and rice-growing areas of East Texas and Louisiana, and by 2012 it was reported on noncrop host plants in Florida. Efforts to suppress E. loftini in United States sugarcane with chemicals and biological control agents were unsuccessful, so both tactics were discontinued, and E. loftini infestation of sugarcane has continued unchecked. During the last 15 years, however, research has focused on the pest’s ecology, improved insecticides and scouting methods, the identification of sugarcane resistance mechanisms, and new cultural tactics. A surveillance technique was developed that indicates when larvae are most vulnerable to insecticide sprays. Currently, registered insecticides for E. loftini control are not widely applied, although some show promise, including an insect growth regulator. A number of potentially useful cultural practices are available, including plowing under fallow stubble, judicious use of fertilizer, adequate irrigation, avoiding proximity to E. loftini-susceptible maize cultivars, and enhancement of natural enemy populations. Demonstrated and potentially useful sugarcane resistance mechanisms involve physiochemical attributes, physical characteristics, and transgenic cultivars.

Assessing resistance of sugarcane varieties to sugarcane borer Diatraea saccharalis Fab. (Lepidoptera: Crambidae)

In this study, we investigated resistance traits to the sugarcane borer Diatraea saccharalis Fab. (Lepidoptera: Crambidae) in the leaves and stalks of six sugarcane cultivars in a series of greenhouse and laboratory assays. Investigation of plant factors and infestation rates to better discriminate stalk damage by the sugarcane borer indicated that infestation of 7-month-old, single plants with 20 larvae at the third or fourth instar per plant was suitable to assess tunneling length. Three cultivars (i.e. SP803280, RB928064, and RB835486) had lower stalk damage (i.e. tunnel length) than cultivar SP891115, which exhibited relatively greater susceptibility to tunneling by the borer. The time required for the larvae to enter the sugarcane stalk was longer for cultivar SP803280, indicating resistance traits on the stalk surface, which correlated with lower stalk damage. Larvae feeding on SP813250 stalks had the lowest weight gain, indicating that this cultivar has resistance traits to larval development within its stalks. Cultivars RB867515 and SP891115 resulted in the highest mortality of early-stage larvae feeding on leaves, indicating the presence of resistance factors in their leaves. Multi-trait cluster and principal component analyses placed the cultivars into three and four clusters, respectively. The cultivars placed in different groups that exhibited resistance to leaf feeding, stalk entrance, and tunneling by the sugarcane borer could be used for crossings in sugarcane breeding programs with the goal of obtaining higher levels of resistance to D. saccharalis.

Oviposition Preference and Survival of the Mexican Rice Borer (Lepidoptera: Crambidae) in Bioenergy and Conventional Sugarcane and Sorghum

Oviposition preference and host suitability of the Mexican rice borer, Eoreuma loftini (Dyar) (Lepidoptera: Crambidae), on bioenergy and conventional cultivars of sugarcane, Saccharum spp., and sorghum, Sorghum spp., were examined in a series of greenhouse experiments. Two energycane cultivars, two sugarcane cultivars, two high-biomass sorghum cultivars, and one sweet sorghum cultivar were assessed at two phenological stages (immature and mature). Mature plants possessed greater availability of dry leaf material compared with immature plants, and all E. loftini eggs were observed exclusively on dry leaves. Oviposition did not vary among host combinations (cultivar by phenological stage); however, eggs per plant and eggs per oviposition event were numerically greater on mature plants than immature plants. In a no-choice experiment, survival from egg to adult did not vary among host combinations, with <2.0% of E. loftini larvae surviving to adulthood. Failed establishment by neonates on plants was 13.4- to 53.9-fold greater than successful establishment across all host combinations. Results from this study suggest that plant physical characteristics continue to play an important role in host selection, but further evaluations will be needed to quantify other characteristics which influence host suitability.

Efficacy of Insect Growth Regulators and Diamide Insecticides for Control of Stem Borers (Lepidoptera: Crambidae) in Sugarcane

Field experiments assessed control of the stem borers, Diatraea saccharalis (F.) and Eoreuma loftini (Dyar), in sugarcane (Saccharum spp.) with selected insect growth regulators and diamide insecticides. Tebufenozide, novaluron, chlorantraniliprole, and flubendiamide were evaluated for D. saccharalis control in four field experiments in Louisiana between 2009 and 2014. Aerial application of the same insecticides was evaluated for control of E. loftini in commercial sugarcane fields in southern Texas in 2012 and 2015. Stalk injury from D. saccharalis in nontreated plots ranged from 7.4-28.1% bored internodes across the four experiments. All insecticides reduced D. saccharalis injury compared with nontreated plots (39.1-99.4% reduction). Better control was achieved with novaluron, flubendiamide, and chlorantraniliprole than with tebufenozide. Pheromone trap-assisted scouting for E. loftini in Texas sugarcane helped to time insecticide applications. Reduced E. loftini injury was observed in diamide-treated plots (3.6-4.7% bored internodes) compared with nontreated controls (13.1%), but not in novaluron- (6.0%) or tebufenozide-treated (8.3%) plots in the 2012 experiment. Significant E. loftini injury was present prior to the aerial insecticide application in 2015, and differences in overall injury were not detected among treatments. However, chlorantraniliprole reduced injury to the top portion of sugarcane stalks. None of the insecticides improved sugar yields in 2012 or 2015. Results suggest insect growth regulators and diamide insecticides fit well in D. saccharalis management programs in Louisiana sugarcane. These chemistries also have potential to improve control of E. loftini, but more research into application strategies is needed to achieve consistent efficacy.

Monitoring Mexican Rice Borer (Lepidoptera: Crambidae) Populations in Sugarcane and Rice With Conventional and Electronic Pheromone Traps

The Mexican rice borer, Eoreuma loftini (Dyar), is a major pest of sugarcane, Saccharum spp., rice, Oryza sativa L., and other graminaceous crops in Texas and Louisiana. The ability of conventional and electronic pheromone traps to monitor E. loftini in sugarcane and rice habitats was evaluated in two separate 2-yr field studies. Bucket traps baited with a synthetic female sex pheromone monitored E. loftini populations in commercial sugarcane fields in Calcasieu and Jefferson Davis Parishes throughout the 2014 and 2015 growing seasons. The number of E. loftini captured differed among months, but not between years or parishes. The percentage of E. loftini-injured stalks was greater in 2015 than in 2014, peaking in September of both years. Daily trap capture was correlated with the percentage of injured stalks. Injury from E. loftini in Louisiana sugarcane remained relatively low (<3% bored internodes) in both 2014 and 2015. In a second experiment, electronic traps were compared with conventional pheromone traps for monitoring E. loftini populations in sugarcane and rice habitats in Texas in 2013 and 2015. Performance of earlier electronic trap prototypes in 2013 was inconsistent and less effective than conventional traps. Improved trap design in 2015 resulted in  more than threefold greater moth capture in electronic traps than in conventional pheromone traps. Electronic traps demonstrated potential to improve monitoring strategies for this pest and should be evaluated for lepidopterous pests in a variety of cropping systems.

Biology and Management of the Mexican Rice Borer (Lepidoptera: Crambidae) in Rice in the United States

The Mexican rice borer, Eoreuma loftini (Dyar), is an invasive pest of rice, Oryza sativa L., in the Gulf Coast region of the United States. This pest also damages sugarcane, Saccharum spp. hybrids; corn, Zea mays L.; and sorghum, Sorghum bicolor (L.) Moench, and feeds on weedy noncrop grasses. Multiple aspects of integrated pest management including use of pheromone traps, manipulation of planting dates, harvest cutting height, stubble management, noncrop host management, soil fertility management, host plant resistance, use of insecticides, and biological control have been studied for Mexican rice borer management. However, the current management strategy in rice primarily relies on the use of chlorantraniliprole insecticide seed treatments. This profile addresses Mexican rice borer biology and management in rice in the United States.