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2017 Annual Report
Objectives
The long-term objective 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 objective enhancing the role of aphid host plant resistance and natural enemies for IPM programs and providing fundamental knowledge of cereal aphid biology and ecology is required. Over the next 5 years we will focus on the following objectives:
Objective 1: Determine the distribution and diversity of resistance-breaking biotypes of cereal aphids in the Great Plains states, identify new sources of resistance for wheat and sorghum, and transfer into suitable genetic backgrounds, to facilitate development of new aphid resistant cereal varieties.
Subobjective 1A: Characterize the biotypic structure of Russian wheat aphid (RWA) populations in wheat and non-cultivated grasses to address biotypic diversity to provide knowledge needed to develop and deploy durable RWA resistance in wheat and barley.
Subobjective 1B: Identify, characterize, and introgress greenbug resistance sources/genes into wheat germplasm.
Objective 2: Determine the distribution and severity of sugarcane aphid in sorghum in the Southwest United States, identify resistant germplasm in sorghum, and evaluate population dynamics to assess the potential for development of resistance-breaking biotypes in this aphid species.
Subobjective 2A: Identify sorghum germplasm with resistance to sugarcane aphid and determine the mechanisms of resistance.
Subobjective 2B: Determine if biotypes exist in sugarcane aphid populations that can overcome sugarcane aphid resistance in sorghum.
Objective 3: Develop and refine methods for field, landscape, and area-wide scale approaches for detecting and monitoring invasive aphid infestations, and optimizing invasive aphid biological control methods in wheat and sorghum.
Subobjective 3A: Develop and refine methods for aphid infestation detection and monitoring in wheat and sorghum based on spatial pattern analysis of multispectral remotely sensed imagery.
Subobjective 3B: Assess resource availability and diversity for the aphid parasite Lysephlebus testaceipes across a range of landscape/agroecosystem diversity levels.
Objective 4: Apply knowledge obtained from aphid genome and transcriptome sequencing to develop plant mediated or other delivery methods for RNAi silencing of critical genes for aphid survival in a broad range of aphids affecting cereals.
Approach
Field and laboratory experiments will be conducted to : (1) characterize the biotypic structure of Russian wheat aphid (RWA) populations in wheat and non-cultivated grasses to address biotypic diversity to provide knowledge needed to develop and deploy durable RWA resistance in wheat and barley; (2) identify, characterize, and introgress greenbug resistance sources/genes into wheat germplasm; (3) identify sorghum germplasm with resistance to sugarcane aphid and determine the mechanisms of resistance; (4) determine if biotypes exist in sugarcane aphid populations that can overcome sugarcane aphid resistance in sorghum; (5) develop and refine methods for aphid infestation detection and monitoring in wheat and sorghum based on spatial pattern analysis of multispectral remotely sensed imagery; (6) assess resource availability and diversity for the aphid parasite Lysephlebus testaceipes across a range of landscape/agroecosystem diversity levels; and (7) apply knowledge obtained from aphid genome and transcriptome sequencing to develop plant mediated or other delivery methods for RNAi silencing of critical genes for aphid survival in a broad range of aphids affecting cereals.
Progress Report
Under Objective 1A, sites were initially located in FY2016 which identified some stable sites to study Russian wheat aphid populations in grasses and wheat. In FY2017, an ARS aphid colony room and genetics lab were modified and sealed for APHIS aphid quarantine approval, which was granted in April and which made this study possible. Field studies in the spring were hampered by rain and snow, therefore, this study will be completed during the fall when cool season grasses and wheat are again available. During these studies data on a new invasive aphid species, Sipha maydis, was obtained and a laboratory colony was established as a resource to identify resistance in wheat and barley. Initial screening results this year found the major sources of greenbug and Russian wheat aphid resistance were susceptible to S. maydis.
Under Objective 1B, a mapping population using a reselection line resistant to greenbug biotype E was developed. The mapping population has been phenotyped, and we are mapping the underlying Gb resistance gene(s). In addition, a backcross population was evaluated in the field, and selected for high yielding lines resistant to both RWA2 and GBE.
Under Objective 2A, through cooperative agreements with Oklahoma State University, two graduate students are continuing mechanisms of resistance in sorghum to sugarcane aphid. This information has facilitated the release of new sources of sugarcane aphid resistant sorghum to the public that resulted through the collaboration with the USDA-ARS laboratories in Stillwater, Oklahoma and Lubbock, Texas. Screening for sources of resistance in 8,000 lines from the sorghum core collection from the National Genetic Resources Program has also been initiated in an effort to identify new sources of sugarcane aphid resistance.
Under Objective 2B, sugarcane aphids were genetically characterized after being collected from sorghum, sugarcane, and Johnson grass across the continental U.S. Three genetically distinct clusters from the Amplified Fragment Length Polymorphism (AFLP) analyses indicated sugarcane aphids were genetically uniform across different host plants and geographic locations. Sugarcane aphid virulence comparisons between a population collected from sugarcane in Florida, and the original population attacking sorghum in Texas in 2013, are currently being examined against diverse sorghum germplasm to determine if the populations are different host races or biotypes. In collaboration with scientists at Oklahoma State University, the genome of sugarcane aphid biotype 1 from central Texas and Louisiana were sequenced and over 200,000 genetic differences between the two populations were found. This information will 1) allow researchers to determine themutation rate, and 2) serve as a reference database to study biotypic variation, insecticide resistance, and other important traits. The sequence information was provided to the USDA laboratories at Ames, Iowa; Lincoln, Nebraska; Manhattan, Kansas; Beltsville, Maryland; and Hilo, Hawaii as a team effort to sequence the Sugarcane aphid genome.
Under Objective 3A, imagery was acquired of eight sugarcane aphid infested grain sorghum fields in Oklahoma and Kansas. A time sequence of imagery of selected fields was acquired for the purpose of determining change over time in reflectance and spatial pattern of sugarcane aphid infestations in grain sorghum fields. Imagery was also acquired for fields without sugarcane aphid infestations for purposes of comparison.
Under Objective 3B, nine greenhouse grown plants (wheat or canola) infested with bird cherry-oat aphids (wheat) or turnip aphids (canola) were placed in each of seven study fields of wheat and canola. The study was repeated twice during the growing season, once in late October and a second time in mid-March. The plants were left in the field for three days and then caged and returned to the greenhouse where they were maintained for 7 days to allow any parasitoids to develop to the pupal stage. Adult parasitoids from plants were counted and identified to species. A suction vacuum sampler was used to obtain an estimate of the density of aphids in each field on approximately the day plants were placed in that field. Parasitoid exclusion cage experiments were conducted in each wheat field in late October and again in mid-March in each wheat and canola field. The experiments ran for four weeks in both autumn and spring. At the end of four weeks the foliage from within each cage was cut and transported to the laboratory. The numbers of aphids and mummified aphids were determined for each cage.
Under Objective 4, bioassays on dsRNA constructs for aphid control are ongoing. Constructs ATPase, Lethal2G, Synaptobrevin and vATPase were made and tested at various concentrations on Russian wheat aphid and greenbug but did not achieve mortalities over 20%. New constructs will continue to be made and tested to find those that give at least 75% mortality before dosage/mortality and time mortality experiments can be conducted. Salivary protein analysis of sugarcane aphid has been initiated to broaden our database on aphid salivary proteomes, identify conserved sequences to target with RNAi, and to determine is biotypes exist between sorghum and sugarcane populations.
Accomplishments
1. New sources of sugarcane aphid resistant germplasm have been identified. New sources of sugarcane aphid resistant germplasm have been identified in collaboration with researchers at Texas A&M University and are being released to the public for breeding purposes. Two sugarcane aphid resistant sorghum lines have been identified by ARS scientists in Stillwater, Oklahoma, in collaboration with USDA-ARS scientists in Lubbock, Texas, and will also be released to the public. Studies on resistance mechanisms in sorghum to sugarcane aphid has also identified a sorghum germplasm which has a high degree of aphid repellence and offers a novel resistance gene to pursue. Altogether these studies provided new sources of sugarcane aphid resistance to sorghum breeders.
2. RNAi research has resulted in a new U.S. Patent. The RNAi research has resulted in a new U.S. Patent (US #9,580,709) entitled "Double stranded RNA constructs for aphid control" in 2017 by ARS scientists in Stillwater, Oklahoma. Two new double stranded RNA constructs, Sucrase and Chloride Intracellular Channel (CLIC) are described which can be expressed in plants or delivered as a spray to silence specific genes in aphids and kill them via RNA interference. These RNAi constructs were designed to target gene regions conserved across aphid species in order to control the broad range of aphid species attacking U.S. crops and provides new pest control tools for the pesticide and plant breeder industries.
3. Remote sensing for monitoring sugarcane aphid infestations. New methods based on multispectral remote sensing from manned aircraft and unmanned aerial vehicles (UAV) was developed for monitoring sugarcane aphid infestations. Research by ARS scientists at Stillwater, Oklahoma, was done in collaboration with researchers at Texas A&M University, College Station, Texas, and Texas A&M University, Corpus Christi, Texas. UAV based normalized difference vegetation index (NDVI) measurements were compared with NDVI from sensors onboard manned aircraft for aphid infestation in sorghum. The UAV and manned aircraft measured both plant height and NDVI. These data were correlated to plot averages of yield and sugarcane aphid density. These methods progress towards the development of a new, efficient, and inexpensive technology for detecting and monitoring sugarcane aphid infestations in grain sorghum fields for purposes of pest management decision making for approximately 4.5 million acres of grain sorghum vulnerable to sugarcane aphid infestation.
Review Publications
Bowling, R., Brewer, M.J., Kerns, D.L., Gordy, J., Seiter, N., Elliott, N.C., Buntin, D.G., Way, M.O., Royer, T.A., Biles, S.P., Maxson, E. 2016. Sugarcane aphid (Homoptera: Aphididae): A new pest on sorghum in North America. Journal of Integrated Pest Management. 7(1):12. doi:10.1093/jipm/pmw011.
Armstrong, J.S., Mbulwe, L., Sekula-Ortiz, D., Villenueva, R.T., Rooney, W.L. 2017. Resistance to Melanaphis sacchari (Hemiptera: Aphididae) in forage and grain sorghums. Journal of Economic Entomology. 110(1):259-265.
Elliott, N.C., Brewer, M., Seiter, N., Royer, T., Bowling, R., Backoulou, G., Gordy, J., Giles, K., Lindenmayer, J., McCornack, B., Kerns, D. 2017. Sugarcane aphid spatial distribution in grain sorghum fields. Southwestern Entomologist. 42(1):27-35.
Giles, K.L., McCornack, B.P., Royer, T.A., Elliott, N.C. 2017. Incorporating biological control into IPM decision making. Current Opinion in Insect Science. 14:1-6.
Medina, R.F., Armstrong, J.S., Harrison, K. 2017. Genetic population structure of sugarcane aphid, Melanaphis sacchari, in sorghum, sugarcane, and Johnsongrass in the continental USA. Entomologia Experimentalis et Applicata. 162(3):358-365.
Puterka, G.J. 2017. More virulent offspring result from hybridization of invasive aphid species, Diuraphis noxia (Hemiptera: Aphididae), with Diuraphis tritici endemic to the United States. Journal of Economic Entomology. 110(2):731-738.
Stanton, C., Starek, M., Elliott, N.C., Brewer, M., Maeda, M., Chu, T. 2017. Unmanned aircraft system-derived crop height and normalized difference vegetation index metrics for sorghum yield and aphid stress assessment. Journal of Applied Remote Sensing (JARS). 11(2):026035. doi:10.1117/1.JRS.11.026035.
Knutson, A.E., Giles, K.L., Royer, T.A., Elliott, N.C., Bradford, N. 2017. Application of pheromone traps for managing Hessian fly, (Diptera: Cecidomyiidae) in the Southern Great Plains. Journal of Economic Entomology. 110(3):1052-1061.
Puterka, G.J., Nicholson, S.J., Cooper, W.R. 2017. Survival and feeding rates of four aphid species (Hemiptera: Aphididae) on various sucrose concentrations in diets. Journal of Economic Entomology. 110(4):1518-1524.
