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

Silicon applications in rice plants alter the stylet probing behaviors of Glyphepomis spinosa (Hemiptera: Pentatomidae)

The stink bug Glyphepomis spinosa Campos & Grazia (Hemiptera: Pentatomidae) is a potential rice pest in Brazil. This study evaluates the interaction between silicon sources and 3 rice cultivars (BRS Esmeralda, Canela de Ferro, and IRGA 417) and examines how increasing silicon levels affect the stylet probing behavior of G. spinosa. The experiment was set up in a completely randomized design with a 3 × 3 factorial scheme (silicon sources: calcium silicate, potassium silicate, a control, and 3 rice cultivars). Fertilizing rice plants with Si altered the probing behavior of the stink bug G. spinosa. The cultivar interaction by Si source was significant in a few variables. This was evidenced by longer periods without ingestion, prolonged time to the first stylet probe (initial probing), and less time spent in cellular maceration. This result supports the use of electropenetrography as a tool to evaluate resistance inducers in plants.

Stem borer herbivory dependent on interactions of sugarcane variety, associated traits, and presence of prior borer damage

BACKGROUND

Herbivory risk is mediated by plant traits related to nutrition and defense that can vary within a species by genotype and age. Prior herbivore damage accrued by a plant can also interact with these traits to alter future herbivory potential by changing plant quantity or quality. Sugarcane (Saccharum spp.) is a perennial crop where aboveground biomass is harvested annually and with varieties differing in nutrition and defenses, making it conducive to evaluating varietal resistance mechanisms. Using data from 16 sugarcane varieties and 28 years, we assessed damage from the primary pest in Louisiana, the sugarcane borer (Diatraea saccharalis, SCB), relative to variety, crop year (ratoon), plant traits, and incidence of prior herbivory.

RESULTS

SCB damage differed among varieties but not crop year, mostly following previously established classifications of SCB resistance, and correlated with select nutritional and defense traits. Within a crop year, the probability of SCB damage increased with prior conspecific damage on the same stalk. However, the strength of this prior damage effect did not match known resistance patterns but still differed with variety.

CONCLUSIONS

Interactions of plant variety, traits, and prior pest damage but not age impacted sugarcane borer risk. Borer damage was associated with nutritional traits of fiber and sugar content, but not consistently with defensive traits like high stalk wax or hair density, indicating there may be additional resistance traits or indirect impacts of these traits on predators. Published 2023. This article is a U.S. Government work and is in the public domain in the USA.

Integrated transcriptome and metabolome analysis revealed that flavonoids enhanced the resistance of Oryza sativa against Meloidogyne graminicola

Rice is a crucial food crop worldwide, but its yield and quality are significantly affected by Meloidogyne graminicola is a root knot nematode. No rice variety is entirely immune to this nematode disease in agricultural production. Thus, the fundamental strategy to combat this disease is to utilize rice resistance genes. In this study, we conducted transcriptome and metabolome analyses on two rice varieties, ZH11 and IR64. The results indicated that ZH11 showed stronger resistance than IR64. Transcriptome analysis revealed that the change in gene expression in ZH11 was more substantial than that in IR64 after M. graminicola infection. Moreover, GO and KEGG enrichment analysis of the upregulated genes in ZH11 showed that they were primarily associated with rice cell wall construction, carbohydrate metabolism, and secondary metabolism relating to disease resistance, which effectively enhanced the resistance of ZH11. However, in rice IR64, the number of genes enriched in disease resistance pathways was significantly lower than that in ZH11, which further explained susceptibility to IR64. Metabolome analysis revealed that the metabolites detected in ZH11 were enriched in flavonoid metabolism and the pentose phosphate pathway, compared to IR64, after M. graminicola infection. The comprehensive analysis of transcriptome and metabolome data indicated that flavonoid metabolism plays a crucial role in rice resistance to M. graminicola infection. The content of kaempferin, apigenin, and quercetin in ZH11 significantly increased after M. graminicola infection, and the expression of genes involved in the synthetic pathway of flavonoids also significantly increased in ZH11. Our study provides theoretical guidance for the precise analysis of rice resistance and disease resistance breeding in further research.

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.

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.

Few Sensory Cues Differentiate Host and Dead-End Trap Plant for the Sugarcane Spotted Borer Chilo sacchariphagus (Lepidoptera: Crambidae)

The use of Erianthus arundinaceus as a trap plant in association with sugarcane reduces populations of the spotted sugarcane stalk borer Chilo sacchariphagus (Bojer) (Lepidoptera: Crambidae). This grass acts as a dead-end trap crop because it is the preferred plant for oviposition relative to sugarcane, and it precludes larval development. We explored the chemical mechanisms involved in host choice by C. sacchariphagus. We showed that the insect's antennal receptors are particularly sensitive to the shared compounds found in the volatile emissions produced by sugarcane and E. arundinaceus. In accordance with their phylogenetic proximity, the two plant species share many physicochemical properties, which suggests that C. sacchariphagus has few sensory cues to differentiate between the two. The terpene (E)-β-ocimene is constitutively emitted by E. arundinaceus, but not by sugarcane. It elicits an electroantennographic response and behavioral responses from female C. sacchariphagus in Y-tube bioassays. Our study suggests that the sensory confusion between host plants, combined with a marginal sensory difference orienting the choice of an egg-laying site, constitutes a mechanism that is relevant to trap cropping. Systems based on this type of mechanism could provide long-term protection for crops vulnerable to insect pests.

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.