1a. Objectives (from AD-416)
The long-term objective of this project is to improve integrated pest management (IPM) practices for cereal aphids in wheat, sorghum, and barley in the United States. Achieving this objective will result in tools and knowledge to enhance the role of host plant resistance and natural enemies in IPM programs for cereal aphids, and fundamental knowledge of cereal aphid biology and ecology required for more effective crop management. Over the next 5 years we will focus on the following objectives: Objective 1: Determine the genetic and biochemical basis for biotype formation in the Russian wheat aphid and greenbug by identifying salivary proteins, genes, and quantitative trait loci associated with virulence. Subobjective 1A. Produce a systematic revision of greenbug, Schizaphis graminum (Rondani) sensu lato (i.e., in the wide sense), based on molecular methods. Subobjective 1B. Map virulence and avirulence loci to wheat resistance genes in the Schizaphis graminum genome. Subobjective 1C. Identify and characterize the salivary proteins injected during feeding by the Russian wheat aphid. Subobjective 1D. Identify physiological and biochemical attributes that confer plant resistance to cereal aphids. Objective 2: Monitor and characterize the biotypic structure of cereal aphid populations in the United States, and develop methods to efficiently determine their biotypic status. Subobjective 2A. Determine the biotypic diversity in Russian wheat aphid populations at a regional level. Subobjective 2B. Characterize holocyclic reproduction in the Russian wheat aphid and its role in biotype evolution. Subobjective 2C. Characterize the role of non-cultivated grass species on the biotypic composition of greenbug populations and their occurrence, along with other cereal aphids, in small grain cropping systems. Objective 3: Assess the effectiveness of key biological control agents in traditional and emerging small grain crop production systems and elucidate the intra- and extra-field processes that influence their population dynamics. Subobjective 3A. Elucidate the effect of landscape factors on the population dynamics of the key greenbug parasitoid, Lysephlebus testaceipes. Subobjective 3B. Elucidate the effect of co-occurring cereal aphids on parasitism of greenbug by Lysephlebus testaceipes. Subobjective 3C. Assess the effect of non-cultivated hosts and wide-spread plantings of switchgrass (Panicum virgatum) on the biology, ecology, and tritrophic relationships of Hymenopterous parasitoids of cereal aphids. Objective 4: Expand the existing Greenbug Decision Support System to include Russian wheat aphid IPM decision support.
1b. Approach (from AD-416)
Field and laboratory experiments will be conducted to: (1) produce a systematic revision of greenbug based on molecular methods; (2) map virulence and avirulence loci to wheat resistance genes in the greenbug genome; (3) identify and characterize the salivary proteins injected during feeding by the Russian wheat aphid; (4) identify physiological and biochemical attributes that confer plant resistance to cereal aphids; (5) determine the biotypic diversity in Russian wheat aphid populations at a regional level; (6) characterize holocyclic reproduction in the Russian wheat aphid and its role in biotype evolution; (7) characterize the role of non-cultivated grass species on the biotypic composition of greenbug populations and their occurrence, along with other cereal aphids, in small grain cropping systems; (8) elucidate the effect of landscape factors on the population dynamics of the key greenbug parasitoid, Lysephlebus testaceipes; (9) elucidate the effect of co-occurring cereal aphids on parasitism of greenbug by L. testaceipes; (10) assess the effect on non-cultivated hosts and wide-spread plantings of switchgrass on the biology, ecology, and tritrophic relationships of Hymenopterous parasitoids of cereal aphids; and (11) develop sophisticated decision support computer software for greenbug and Russian wheat aphid pest management decision support that is comprehensive in scope yet easy for end users to understand and operate.
3. Progress Report
Amino acid sequences of aphid salivary proteins: Salivary proteins that the Russian wheat aphid and greenbug inject into wheat have been identified, and comparisons were made between the biotypes that occur within these species. Using LC-MS/MS, we identified over 34 proteins in Russian wheat aphid saliva. In addition, we have sequenced the genome of the Russian wheat aphid and are presently identifying novel proteins that will be added to the Genebank databases. Regional Russian wheat aphid biotypes collected: During the spring of 2011, we were successful in making over 350 collections from Texas, Colorado, New Mexico, Oklahoma, Kansas, Utah, and Wyoming for biotype assessments. Occurrence of Russian wheat aphid–western wheat aphid crossbreeding: Russian wheat aphid and western wheat aphid (Diuraphis tritici) populations were collected from known high altitude egg-stage overwintering locations in western Colorado. Under greenhouse conditions, both male and female production occurred in western wheat aphid; however, only oviparous females were produced by Russian wheat aphid. Crossbreeding experiments between western wheat aphid males and Russian wheat aphid oviparae proved successful and resulted in Russian wheat aphids producing fertile eggs that were hatched under laboratory conditions. Notably, the Russian wheat aphid offspring were more virulent than their parents to all wheat resistance sources. Suitability of switchgrass as a host for cereal aphids: Potential widespread plantings of switchgrass for use in the cellulosic production of ethanol prompted its evaluation as a suitable host for economically important cereal aphids. Preliminary results indicated that switchgrass was not a suitable host for greenbug biotype E or Russian wheat aphid biotype 2, the two most prevalent and economically important cereal aphids. However, switchgrass is a suitable host for greenbug biotype I, bird-cherry oat aphid, corn leaf aphid, and yellow sugarcane aphid. There were no switchgrass by cultivar effects discerned; however, clear differential plant responses to the greenbug biotypes were observed, suggesting the potential for developing greenbug biotype-specific resistant cultivars. Functional response model for convergent lady beetles: The ability to predict predation on cereal aphids by arthropod predators is critical to developing predictive pest management decision support systems. We developed and tested a Holling Type II functional response model for convergent lady beetles foraging on cereal aphids. We found no statistically significant bias in model predictions, indicating that the model provided a reasonable description of the functional response; however, high variation in observed versus predicted predation rates was evident, which may reflect the inherent high variability in all aspects of the foraging process by the beetles. We are using the model to refine a pest management decision support system for the greenbug and to develop a similar system for Russian wheat aphid.
1. Sequence of Russian wheat aphid genome and identification of aphid salivary proteins. Sequencing the Russian wheat aphid genome and identifying aphid salivary proteins are essential for discovery of new genetic sources of resistance for use in wheat transformation systems to produce wheat plants with new mechanisms of genetic resistance to the aphid pest. The genomes of Russian wheat aphid biotypes 1 and 2 were sequenced and a draft assembly completed. Salivary proteins that were common or unique among biotypes of Russian wheat aphid and greenbug were identified. An invention report was filed on 30+ salivary proteins of Russian wheat aphids that will be valuable in developing RNAi gene silencing technology that can be used to protect plants from Russian wheat aphids, or sucking insects in general. The significance of this accomplishment lies in providing potential genes conferring host plant resistance via novel genetic mechanisms to the wheat breeding industry for use in genetic transformation systems for wheat.
Backoulou, G., Elliott, N.C., Giles, K., Phoofolo, M., Catana, V. 2011. Development of a method using multispectral imagery and spatial pattern metrics to quantify stress to wheat fields caused by Diuraphis noxia. Computers and Electronics in Agriculture. 75:64-70.