Project : USDA ARS

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Research Project: Management Strategies for Invasive Aphid Pests of Cereals

Location: Peanut and Small Grains Research Unit

2024 Annual Report

Objectives
The long-term goal of this project is to improve integrated pest management (IPM) practices for cereal aphids in wheat, barley, and sorghum in the United States. To achieve this goal, we will increase the knowledge of aphid host plant resistance and natural enemies for IPM programs and provide fundamental knowledge of cereal aphid biology and ecology. Over the next 5 years we will focus on the following objectives: OBJECTIVE 1: Determine regional distribution and significance of invasive aphid species on cereals and alternate grass hosts, discover changes or shifts in the populations, generate relevant phenotypic information, and work with breeders or geneticists to map and pyramid resistant genes. Subobjective 1A: Determine the biotype diversity of the S. Maydis known as the hedgehog aphid (HGA) in cereals and native grasses in advance of discovering and utilizing resistant sources used in breeding for resistance. Subobjective 1B: Identify wheat germplasm resistant to HGA, as well as wheat accessions resistant to all U.S. RWA biotypes. Subobjective 1C: Characterize RWA and HGA resistance genes and develop molecular markers for their introgression into locally adapted breeding lines and cultivars. OBJECTIVE 2: Determine the biological differences and interactions among available sugarcane aphid resistance genes, including comparisons of cross-resistance genes, elucidate resistance mechanisms, and work with breeders and geneticists to map, pyramid, and deploy resistant genes. Subobjective 2A: Develop forage sorghum germplasm resistant to sugarcane aphids. OBJECTIVE 3: Develop effective multi-scale aphid infestation monitoring and sampling technology, develop geographically explicit cereal aphid pest infestation risk models, and elucidate and integrate field and landscape-level components of the natural enemy populations into improved management systems for invasive cereal aphids. Subobjective 3A: Use field research methods and statistical modeling and hypothesis testing to develop a detailed understanding of spatial and temporal factors that determine colonization, population dynamics, and community development of aphid natural enemies in grain sorghum fields and their importance for sugarcane aphid biological control. Subobjective 3B: Develop and disseminate new, time-efficient, and statistically accurate and precise methods for sampling aphid natural enemies in sorghum.

Approach
The combined annual economic value of wheat, sorghum, and barley within the United States is over $16 billion. Cereal aphids are major pests of world agriculture that vector numerous plant viruses and remove photoassimilates by inserting their mouthparts into the sieve elements of the phloem tissue. The direct loss from feeding and the transmission of viral diseases during the process of feeding make cereal aphids the most significant threat to U.S. cereal crop producers. Although aphids in general are small in size, the reproductive potential is at the higher end of the spectrum when compared to all arthropods, with exponential increases and short generation times. Significant yield reductions occur from the direct effect of endemic or epidemic aphid populations. New information on the factors affecting insect populations and new integrated pest management (IPM) tools, control technologies, and aphid-resistant germplasm are needed in order to advance sustainable IPM programs for cereals. The objectives of this project that will deliver the associated products to the consumer are to: 1) determine the biotypic diversity in aphid populations which threatens deployment of aphid-resistant cereals; 2) identify new sources of resistance to aphids in wheat and sorghum and barley; 3) determine the extent and severity of new aphid pest species attacking cereal crops; and 4) develop or refine methods for detecting and monitoring aphid infestations to optimize biocontrol in cereals. The specifically designed research provided in this plan will increase our knowledge on the genomics of virulent cereal aphid biotypes within the U.S. and increase the knowledge of available genetic sources of resistance in wheat, barley, and sorghum. Once identified these resistant sources will be introgressed into available breeding lines. In addition, the benefits and ecological associations of beneficial insects in the agricultural landscape will be better understood and utilized as a result of areawide studies on these organisms.

Progress Report
Progress towards Objective 1C during FY24 involved developing three plant populations to map Russian wheat aphid (RWA) and hedgehog grain aphid (HGA) resistance genes. Two F2:3 populations from crosses PI 625139 × OK11D25060 and PI 626575 × Jagalene were genotyped using Genotyping-by-Sequencing (GBS) and were evaluated for responses to U.S. RWA biotypes. A RWA resistance gene conferring resistance to all U.S. RWA biotypes, designated Dn625139, was identified in chromosome arm 7DS in PI 625139, while the RWA resistance gene in PI 626575, designated Dn626575, was mapped to chromosome arm 7DL. User-friendly, high throughput Kompetitive Allele Specific PCR (KASP) markers have been developed to facilitate introgression of both RWA resistance genes into locally adapted lines. Progress towards Objective 3A during FY24 involved developing a detailed understanding of spatial and temporal factors that determine colonization, population dynamics, and community development of aphid natural enemies in grain sorghum fields and their importance for sugarcane aphid biological control. Data on field population dynamics of sorghum aphid and natural enemies collected over seven years in over 200 sorghum fields each sampled approximately weekly throughout the growing season for 7 growing seasons were collated and merged with data on landscape structure and weather for each field. In total there are over 130,000 data records each with over sixty independent and dependent variables. Progress towards Objective 3B during FY24 was made by collecting data from laboratory experiments to measure predation rates by key insect natural enemies of sorghum aphid. The natural enemies were a common green lacewing species that occurs in sorghum fields, a common lady beetle species in sorghum, and a parasitoid that parasitizes sorghum aphid in sorghum fields. One manuscript was written that describes research on parasitism levels of sorghum aphid by the parasitoid species and the parasitoids ability to switch between aphid host species in sorghum. Progress towards Objective 3B during FY24 also was made by comparing sampling methods for aphid natural enemies for 23 full replications of a field study to evaluate sampling methods for natural enemies. Aphid and natural enemy densities varied markedly among experimental fields indicating that the data will be valuable for model development and validation. The data represent sorghum aphid populations that are well below economic thresholds to populations that exceed economic thresholds.

Accomplishments
1. Modeling sorghum aphid migration and population dynamics in grain sorghum. Sorghum aphid, Melanaphis sorghi (Theobald, 1904) is a severe invasive pest of sorghum causing millions of dollars in losses annually to growers from grain sorghum yield losses and insecticide application costs. ARS researchers in Stillwater, Oklahoma, developed models to evaluate the effect of weather and other abiotic and biotic factors on sorghum aphid infestation of sorghum fields. The models identified windspeed and direction at multiple levels of the atmosphere as directly impacting seasonal migration of sorghum aphid and colonization of sorghum fields in the Southern and Central Plains states. Biotic factors such as natural enemies of sorghum aphid influenced sorghum aphid population growth in fields. Models showed that southerly wind direction and speed determined the distance of northward migration of sorghum aphids. Results of modeling form a basis for understanding and predicting sorghum aphid colonization and population fluctuation in sorghum fields to assist in production planning for sorghum producers.

2. Discovery of a gene conferring resistance to U.S. Russian wheat aphid biotypes. Russian wheat aphid (RWA, Diuraphis noxia Kurdjumov) is a highly invasive and destructive wheat pest evolving rapidly to overcome host plant resistance. Novel genes conferring resistance to multiple RWA biotypes are needed to sustain wheat production. ARS scientists in Stillwater, Oklahoma, and Manhattan, Kansas, identified a new gene, designated Dn625139, conferring resistance to all U.S. RWA biotypes in the short arm of chromosome 7D in the Iranian landrace PI 625139, and developed high throughput, user-friendly Kompetitive Allele Specific PCR (KASP) markers linked to Dn625139. Dn625139 can be widely used to develop resilient wheat cultivars in U.S. wheat breeding programs, and KASP markers developed in this study can facilitate rapid introgression of Dn625139 into locally adapted breeding lines.

U.S. DEPARTMENT OF AGRICULTURE

Peanut and Small Grains Research Unit: El Reno, OK