Seasonal infestations of two stem borers (Lepidoptera: Crambidae) in noncrop grasses of Gulf Coast rice agroecosystems

The Structure of Rice Stemborer Assemblages: A Review of Species' Distributions, Host Ranges, and Interspecific Interactions

This review describes global rice stemborer assemblages based on published species distributions, apparent host preferences, and reported shifts in assemblage composition in response to environmental factors. At least 56 moth (Lepidoptera: Crambidae, Pyralidae, Noctuidae) and fly (Diptera: Diopsidae, Chloropidae) species have been associated with rice; however, only 21 species are of potential, large-scale economic importance with a further 2 species of localized concern; most of the remaining species' associations with rice are based on dubious records without economic impacts on rice production. A list of stemborer-host associations indicates that rice stemborers are largely oligophagous on grasses (Poaceae), but a few species are polyphagous (also attacking Cyperaceae, Typhaceae, and some Eudicotyledon plants). Total stemborer abundance is determined by rice cropping patterns and management. Assemblage species richness is determined by geographical location, surrounding habitat (particularly as regards secondary and occasional species), and season. Evidence suggests that stemborer assemblage structure is largely determined through conditional interspecific competition. Regional assemblages typically include a single dominant lepidopteran species (primary species) that is largely restricted to rice and for which the climate is optimal; one or more secondary species that vary based on the age of rice attacked, rice anatomy, and the proximity to other habitats (including other crops); and occasional species that probably spill over from adjacent grasslands. The co-occurrence of lepidopteran with dipteran rice stemborers requires further research attention.

Spatial Distribution of Lepidopteran Stem Borers in Louisiana Rice Fields

Louisiana rice is attacked by a complex of lepidopteran stem borers that injure the vegetative and reproductive stages of rice, reducing tillering and grain output. Currently, insecticidal seed treatments are used in Louisiana as a preemptive means to control stem borers in rice. Our objective was to better understand the spatial distribution of stem borers in Louisiana rice fields. Thirteen nontreated commercial rice fields in Louisiana were mapped using GPS software and surveyed for stem borer damage in 2017 and 2018. Damage was recorded by counting the number of blank panicles (whiteheads) within quadrats located at different areas in each field. An ANOVA, spatial interpolation, hotspot analysis, and negative binomial regression were used to determine where stem borer injury was concentrated and whether the distribution of these pests was influenced by rice stand count, field composition, and site location. The results show that stem borers are typically aggregated along field edges, with population density decreasing toward the center of rice fields. Stem borer damage was 4.2- and 3.9-fold greater along field edges than in field centers in 2017 and 2018, respectively. Hotspot spatial analysis revealed 41.7 and 52.1% of low-density clusters occurred at or near field centers, respectively. Negative binomial regression revealed stem borer injury declines with increasing distance from field edges, with regional differences in infestation levels. This suggests stem borer control efforts could be spatially targeted to improve the efficiency of pest management.

Stem borers revisited: Host resistance, tolerance, and vulnerability determine levels of field damage from a complex of Asian rice stemborers

Yield losses from rice stem borers depend on the nature of the rice variety, the timing of attack, and the composition of the stem borer species assemblage. This study uses a range of phenotyping methods to distinguish different categories of herbivore-rice interaction that determine relative damage levels (dead heart and whitehead-panicles) and yield losses to varieties exposed to stem borers. Phenotyping studies were conducted in a greenhouse, screen house and field using two stem borer species (Scirpophaga incertulas [yellow stem borer - YSB] and Chilo suppressalis [striped stem borer - SSB]) and 12 rice lines. Only YSB displayed oviposition preferences across rice varieties. Both stem borer species performed better (greater survival, shorter development times, heavier pupae) on rice at vegetative compared to reproductive growth stages, and SSB was less capable than YSB of developing on rice at reproductive growth stages. Stem borer larval survival, body weight, development time, and tiller damage across different rice varieties in greenhouse experiments was poorly correlated between the two stem borer species and for each of the species on rice at two different plant growth stages (vegetative and reproductive). In contrast, rice tillering and yield responses to the two stem borer species were often highly correlated, but only when plants were attacked at the reproductive stage. Short-term, controlled experiments revealed aspects of host resistance and relative changes in plant biomass and yield in response to damage (condition change). However, the results from controlled environments and field-plots were not generally correlated because plant vulnerability, i.e., relative exposure to stem borer attack due to crop duration, largely determined field damage. We recommend that phenotyping studies should differentiate between the resistance, tolerance and vulnerability of rice lines to complexes of stem borers in a given region. Single stem borer species experiments under controlled environments are useful to gain knowledge of the nature of rice-stem borer interactions; however, field testing with comparative treatments, particularly under high soil fertilizer levels that increase plant attractiveness, are better for assessing the relative propensities of rice varieties to incur damage and yield losses due to complexes of stem borers.

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.

The Sugarcane Borer (Lepidoptera: Crambidae) Infests Rice at Low Population Levels in Florida

The sugarcane borer, Diatraea saccharalis (F.), rice stalk borer, Chilo plejadellus Zincken, and Mexican rice borer, Eoreuma loftini (Dyar), are stem borers (Lepidoptera: Crambidae) that infest rice (Oryza sativa L.) in the southern United States. A 2-yr study was conducted to determine stem borer injury, infestation, and parasitism levels in Florida. Thirty commercial rice fields were selected during the 2017 and 2018 growing seasons throughout the rice production region in southern Florida. Sampling for stem borer injury and infestations was conducted in each field between the milk and early maturation stages by observing plants at 10 locations, with three 1-m2 quadrats per location. In addition, monitoring for E. loftini adults was conducted using one pheromone trap adjacent to each field. In 2017, the number of rice tillers exhibiting stem borer injury averaged 0.024 tillers/m2 and infestation levels averaged 0.008 stem borers/m2, with only D. saccharalis being observed. In 2018, injury and infestation levels averaged 0.062 injured tillers/m2 and 0.023 D. saccharalis larvae or pupae/m2, respectively. The solitary parasitoid Alabagrus stigma Brullé (Hymenoptera: Braconidae) parasitized 33 and 40% of the collected D. saccharalis in 2017 and 2018, respectively. In addition, pheromone traps did not capture E. loftini adults. This study shows that D. saccharalis infests rice in Florida but at relatively low levels not threatening production and that rice fields are habitats for D. saccharalis parasitoids. This study also suggests that C. plejadellus and E. loftini do not occur in southern Florida.

Influence of historical land use and modern agricultural expansion on the spatial and ecological divergence of sugarcane borer, Diatraea saccharalis (Lepidoptera: Crambidae) in Brazil

Human-mediated changes in landscapes can facilitate niche expansion and accelerate the adaptation of insect species. The interaction between the evolutionary history of the sugarcane borer, Diatraea saccharalis Fabricius, and historical and modern agricultural activity in Brazil shaped its spatial genetic structure, facilitating ecological divergence and incipient host shifting. Based on microsatellite data, STRUCTURE analyses identified two (K = 2) and three (K = 3) significant genetic clusters that corresponded to: (a) a strong signal of spatial genetic structure and, (b) a cryptic signal of host differentiation. We inferred that K = 2 reflects the footprint of agricultural activity, such as expansion of crop production (sugarcane and maize), unintentional dispersion of pests, and management practices. In contrast, K = 3 indicated incipient host differentiation between larvae collected from sugarcane or maize. Our estimates of population size changes indicated that a historical bottleneck was associated with a reduction of sugarcane production ≈200 years ago. However, a more recent population expansion was detected (>1950s), associated with agricultural expansion of large crop production into previously unfarmed land. Partial Mantel tests supported our hypothesis of incipient host adaptation, and identified isolation-by-environment (e.g., host plant) in São Paulo and Minas Gerais states, where sugarcane has been traditionally produced in Brazil. The impact of agricultural production on D. saccharalis may continue, as the current population structure may hinder the efficacy of refuge plants in delaying insect resistance evolution to Bt toxin.

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.

Population Distribution and Range Expansion of the Invasive Mexican Rice Borer (Lepidoptera: Crambidae) in Louisiana

The Mexican rice borer, Eoreuma loftini (Dyar) (Lepidoptera: Crambidae), is an invasive pest that was first introduced into southern Texas in 1980 and has been expanding its range eastward along the United States Gulf Coast. The pest attacks rice (Oryza sativa L.), sugarcane (Saccharum spp.), corn (Zea mays L.), and other graminaceous crops, and its establishment in Louisiana is expected to have severe economic impacts on crop production. Range expansion and population distribution of E. loftini were monitored with a network of 77 pheromone traps throughout southwestern Louisiana from 2013 to 2015. Eoreuma loftini was ubiquitous throughout the study region, with male moths captured in every habitat sampled. Spatial analysis revealed the population is characterized by high and low density clusters, with the greatest trap captures occurring in southeastern Calcasieu Parish and southern Jefferson Davis Parish. Trap captures in more northern regions of the study were lower than in southern parishes. Trap captures in areas where the pest has been established for >3 yr were greatest in rice habitats. The weighted mean population center moved eastward at a rate of ∼11 km per year. Human-aided movement of E. loftini was probably not involved in the eastward expansion documented during this study. Seasonal population peaks were detected in March-April, July-August, and October-November. This study indicates this species is continuing its spread eastward along the United States Gulf Coast and will likely become established throughout Louisiana within the next 20 yr.

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.

Therapeutic effects of late outgrowth endothelial progenitor cells or mesenchymal stem cells derived from human umbilical cord blood on infarct repair

BACKGROUND

This study sought to systematically investigate the derivation of late outgrowth endothelial progenitor cells (late EPC) and mesenchymal stem cells (MSC) from umbilical cord blood (UCB) and to examine their therapeutic effects on myocardial infarction (MI).

METHODS

The expression of angiogenic genes was determined by qRT-PCR. Myocardial infarction (MI) was induced in rats, and cells were directly transplanted into the border regions of ischemic heart tissue.

RESULTS

Culture of UCB mononuclear cells yielded two distinct types of cells by morphology after 2 weeks in the same culture conditions. These cells were identified as late EPC and MSC, and each was intramyocardially injected into rat hearts after induction of MI. Echocardiography and histologic analyses demonstrated that both EPC and MSC improved cardiac function and enhanced vascularization, although fibrosis was reduced only in the EPC transplanted hearts. Different paracrine factors were enriched in EPC and MSC. However, once injected into the hearts, they induced similar types of paracrine factors in the heart. Transplanted EPC or MSC were mostly localized at the perivascular areas. This study demonstrated that EPC and MSC can be simultaneously derived from UCB under the same initial culture conditions, and that common paracrine factors are involved in the repair of MI.

CONCLUSION

Late EPC and MSC are effective for infarct repair, apparently mediated through common humoral mechanisms.

Expansion of the Mexican Rice Borer (Lepidoptera: Crambidae) into Rice and Sugarcane in Louisiana

The Mexican rice borer, Eoreuma loftini (Dyar) (Lepidoptera: Crambidae), is an invasive pest of sugarcane, Saccharum spp., rice, Oryza sativa L., and other graminaceous crops in the Gulf Coast region of the United States. Traps baited with E. loftini female sex pheromones were used to document establishment and distribution of E. loftini near sugarcane, rice, and noncrop hosts in seven southwest Louisiana parishes from 2009 to 2013. Additional field surveys documented larval infestations in commercial sugarcane and rice. After its initial detection in 2008, no E. loftini were detected in Louisiana in 2009 and only two adults were captured in 2010. Trapping documented range expansion into Cameron, Beauregard, and Jefferson Davis parishes in 2011 and Allen, Acadia, and Vermilion parishes in 2013. During the course of this study, E. loftini expanded its range eastward into Louisiana 120 km from the Texas border (≈22 km/yr). Surveys of larval infestations provided the first record of E. loftini attacking rice and sugarcane in Louisiana. Infestations of E. loftini in rice planted without insecticidal seed treatments in Calcasieu Parish reached damaging levels.

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

The Mexican rice borer, Eoreuma loftini (Dyar), is a major pest of sugarcane (hybrids of Saccharum spp.) in Louisiana and Texas. Resistance to E. loftini was evaluated in 51 commercial and experimental cultivars of sugarcane, energycane (hybrids of Saccharum spp.), and sorghum [Sorghum bicolor (L.) Moench and hybrids of Sorghum spp.] in four replicated small plot field experiments from 2009 to 2012. A relative resistance ratio was developed to compare levels of susceptibility among cultivars based on the percentage of bored internodes and survival to adulthood. This index was able to separate cultivars into five resistance categories and provides a new method for comparing levels of resistance among cultivars. E. loftini pest pressure in 2009 was among the highest recorded with injury ranging from 55 to 88% bored internodes. Commercial sugarcane cultivar HoCP 85-845 was identified as resistant in three of four experiments, whereas HoCP 04-838 was identified as susceptible in all experiments. Of the five sugarcane cultivars in commercial production in the Rio Grande Valley of Texas, only TCP 87-3388 was categorized as resistant. Of the cultivars with potential for bioenergy production, all of the energycane cultivars demonstrated higher levels of resistance than high-biomass and sweet sorghum cultivars. Continued evaluation of cultivar resistance to E. loftini is important to development of effective integrated pest management strategies for this pest.

Mexican rice borer (Lepidoptera: Crambidae) injury to corn greater than to sorghum and sugarcane under field conditions

The Mexican rice borer, Eoreuma loftini (Dyar) (Lepidoptera: Crambidae), is the key pest of sugarcane (Saccharum spp.) in Texas; it can attack several grassy crop and noncrop host plants and has spread into Louisiana. Through small-plot, commercial field, and pheromone trap experiments, this study demonstrates that the pest uses corn, Zea mays L., more than sugarcane and sorghum, Sorghum bicolor (L.) Moench, but when corn is harvested in late summer, injury to nearby sugarcane strongly increases during the next approximately equal to 2 mo to harvest. Corn was more infested than sugarcane and sorghum in commercial fields regardless of whether sampling occurred on field edges or farther into field interiors. Differences in numbers of infested stalks and in numbers of larval entry holes between field edges and interiors were not detected. We found that Mexican rice borer infestation of corn can cause loss of ears, and lodging, shattering, and complete destruction of maturing stalks. The larger quantities of adult Mexican rice borers captured in pheromone-based traps placed at corn field edges compared with sorghum and sugarcane field edges further indicates that corn is preferred to sugarcane and sorghum. The basis for the pest's attraction to corn and implications to potential range expansion to other U.S. sugarcane-growing regions are discussed.