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The Russian wheat aphid (RWA, Diuraphis noxia Kurdjumov) is a global pest of wheat (Triticum aestivum L.) that became a significant problem to wheat and barley (Hordeum vulgare L.) in the United States soon after it was detected in 1986. Russian wheat aphid‐resistant wheat varieties expressing the Dn4 gene were effective in managing the first biotype, RWA1, from 1995–2003 until a new biotype, RWA2, overcame this resistance in 2003. Currently, only three genes are useful in developing RWA2 resistance in wheat. A new gene, Dn10, was recently discovered that is resistant to RWA2. This study characterized the effects that RWA1 and RWA2 had on the damage (leaf chlorosis and leaf roll) and growth components (plant height and leaf number) of plants expressing RWA resistance genes Dn4, Dn7, Dn10, Dn2401, Dn626580, and Dn2414 and the susceptible 'Yuma' 22 d after infestation. All plant genotypes that were RWA resistant expressed strong resistance to leaf chlorosis and leaf roll after RWA1 feeding. Results were similar for RWA2 except for the Dn4 genotype, which was equally susceptible as Yuma. Plant height was reduced by 50% for susceptible Yuma and Dn626580 by RWA1 and RWA2 feeding. Plant height and leaf reduction from RWA2 feeding on the susceptible Dn4 genotype were also reduced by 50%, whereas Dn7, Dn10, and Dn2414 reductions were <23%. Dn10 exhibited strong resistance to RWA1 and RWA2 feeding damage comparable with Dn7 and Dn2414 and showed less reduction in plant height than Dn2401 and Dn626580, which makes it a potentially valuable gene for wheat breeding programs. [ABSTRACT FROM AUTHOR]

Sipha maydis Passerini (Heteroptera: Aphididae) is a cereal pest with an extensive geographical range that includes countries in Europe, Asia, Africa, and South America. Reports of S. maydis in the United States have been infrequent since it was first detected in California, 2007. Two studies, focused (NW CO) and multistate (OK, TX, NM, CO, UT, WY), were conducted to determine the distribution and host range of S. maydis in the Rocky Mountain and Southern Plains states over a 3-yr period, 2015–2017. In 2015, focused sampling in NW Colorado found S. maydis at 59% of the 37 sites, primarily on wheat. Sipha maydis did not survive extreme winter temperatures from late December 2015 to early January 2016 that ranged from −9.0 to −20.9°C over a 9-d period, which resulted in no aphids detected in 2016. In the multistate study, S. maydis occurred in 14.6% of 96 sites sampled in 2015, 8% of 123 sites in 2016, and 9% of 85 sites in 2017 at wide range of altitudes from 1,359 to 2,645 m. Sipha maydis occurred mainly in NW and SW Colorado and NE New Mexico along with a few sites in NE Colorado, SE Utah, and SE Wyoming. This aphid mainly infested wheat followed by a variety of eight wild grass species. No parasites, predators, sexual morphs, or significant plant damage occurred at the sites. Sipha maydis utilized 14 hosts in the United States including 8 new host records, which expands its host range to 52 plant species worldwide. Sipha maydis may be of concern to wheat, barley, and sorghum production in the United States if its populations continue to increase. [ABSTRACT FROM AUTHOR]

The Russian wheat aphid, Diuraphis noxia (Kurdjumov), invaded the United States in 1986 and soon became a significant pest of wheat. Diuraphis tritici (Gillette) is native to the United States and was firmly established on wild grasses before the arrival of Russian wheat aphid. Both species are known to coinfest the same grass hosts, during the time they enter the sexual phase in the fall, mate, and produce overwintering eggs. Therefore, we induced males and females under greenhouse conditions in the fall and conducted studies in the laboratory to determine if these two species interbred and produced viable offspring. Fitness and virulence to Russian wheat aphid-resistant wheat and barley entries were also compared among the hybrid progeny and both parents. Diuraphis tritici produced males and females in October. Diuraphis noxia biotype RWA8 produced enough oviparae to conduct crossing experiments. No males occurred in the D. noxia colony making it only possible to crossbreed D. tritici males with RWA8 oviparae and to inbreed D. tritici. No difference in egg production per female (2.0-2.5) or percent egg hatch (23.1-27.0%) was found between crosses. However, progeny survival after hatch for D. tritici inbreds (33.3%) was much higher than the D. tritici × D. noxia crosses (0.25%). Only one hybrid survived to reproductive adult. Intrinsic rate of increase (rm) indicated the hybrid (0.18) was less fit than both parents (0.24-0.29). The hybrid line produced damage ratings to the 16 cereal entries similar to D. tritici but was more virulent to wheat and barley entries than both parents. [ABSTRACT FROM AUTHOR]

Salivary secretions play critical roles in aphid- host plant interactions and are responsible for damage associated with aphid feeding. The objectives of this study were to evaluate aspects of salivation and the salivary constituents of Diuraphis noxia (Hemiptera: Aphididae). Salivary proteins were isolated and compared from three aphid probed diets: pure water, 15% sucrose, or amino acids (100mM serine, 100mM methionine, 100mM aspartic acid, and 15% sucrose). After 6 h, more aphids settled on sucrose diet compared with other diets, but there were no significant differences in the number of stylet sheaths produced per aphid after 24 h. There were differences in the amount of soluble salivary protein (watery saliva), with the greatest amount secreted in sucrose diet, followed by amino acid diet and pure water, respectively. Protein constituents secreted into sucrose and amino acid diets were compared using gel electrophoresis using standardized amounts of protein. More protein bands and bands of greater intensity were visualized from probed sucrose diet compared with probed amino acid diet, indicating qualitative differences. Phosphatase was putatively identified from D. noxia saliva from a major protein band using gel electrophoresis and mass spectrophotometry. Alkaline phosphatase activity was confirmed in sucrose diet using enzymatic assays but was not detected in aphid probed water or amino acid diets. Other peptides in sucrose diet weakly but significantly showed similarities to putative dehydrogenase and RNA helicase expressed sequence tags identified from other aphids. The implications of these findings in aphid salivation and plant-insect interactions are discussed. [ABSTRACT FROM AUTHOR]

The Russian wheat aphid, Diuraphis noxia (Kurdjumov) (Hemiptera: Aphididae), is a serious wheat, Triticum aestivum L., and barley, Hordeurn uulgare L., pest throughout the small grain-producing areas in the western United States. The virulency and classification of recently described Russian wheat aphid biotypes 1-7 (RWA1-7) were clarified using 24 plant differentials. These seven biotypes had been described previously using various methods and test environments; therefore, the purpose of this study was to test them all under uniform environmental conditions. RWA1 was the least virulent of the biotypes tested, with susceptible ratings observed in five plant differentials and intermediate ratings observed in four plant differentials. RWA4, RWA5, RWA6, and RWA7 had intermediate virulence. RWA4, RWA5, and RWA7 share similar responses, with susceptible responses in six plant differentials and intermediate responses in five plant differentials. Small differences within a few plant differentials separate RWA4, RWA5, and RWA7. RWA6 has susceptible responses with only four plant differentials, but 10 plant differentials had intermediate responses. RWA3 was highly virulent, with susceptible responses in 10 plant differentials and intermediate responses in five plant differentials. RWA2 was the most virulent strain tested with susceptible responses to 12 plant differentials and intermediate responses to five plant differentials. This study has demonstrated that RWA1-7 have different combinations of virulence to the plant differentials tested, thereby confirming previous Russian wheat aphid biotype designations. [ABSTRACT FROM AUTHOR]

The biotypic diversity of the Russian wheat aphid, Diuraphis noxia (Kurdjumov) (Hemiptera: Aphididae), was assessed in five isolates collected in Colorado. Three isolates, RWA 1, RWA 2, and an isolate from Montezuma County, CO. designated RWA 6, were originally collected from cultivated wheat, Triticum aestivum L., and obtained from established colonies at Colorado State University. The fourth isolate, designated RWA 7, was collected from Canada wildrye, Elymus canadensis L., in Baca County, CO. The fifth isolate, designated RWA 8, was collected from crested wheatgrass, Agropyron cristatum (L.) Gaertn., in Montezuma County, CO. The four isolates were characterized in a standard seedling assay, by using 24 plant differentials, 22 wheat lines and two barley, Hordeum vulgare L., lines. RWA 1 was the least virulent of the isolates, killing only the four susceptible entries. RWA 8 also killed only the four susceptible entries, but it expressed intermediate virulence on seven wheat lines. RWA 6, killing nine entries, and RWA 7, killing 11 entries, both expressed an intermediate level of virulence overall, but differed in their level of virulence to 'CO03797' (Dnl), 'Yumar' (Dn4), and 'CO960293-2'. RWA 2 was the most virulent isolate, killing 14 entries, including Dn4- and Dny-containing wheat. Four wheat lines, '94M370' (Dn7), 'STARS 02RWA2414-11', CO03797, and 'CI2401', were resistant to the five isolates. The results of this screening confirm the presence of five unique Russian wheat aphid biotypes in Colorado. [ABSTRACT FROM AUTHOR]

Wheat, Triticum aestivum L., with Russian wheat aphid, Diuraphis noxia (Kurdjumov) (Hemiptera: Aphididae) resistance based on the Dn4 gene has been important in managing Russian wheat aphid since 1994. Recently, five biotypes (RWA1-RWA5) of this aphid have been described based on their ability to differentially damage RWA resistance genes in wheat. RWA2, RWA4, and RWA5 are ofgreat concern because they can kill wheat with Dn4 resistance. In 2005,365 Russian wheat aphid clone colonies were made from collections taken from 98 fields of wheat or barley, Hordeum vulgare L., in Oklahoma, Texas, New Mexico, Colorado, Kansas, Nebraska, and Wyoming to determine their biotypic status. The biotype of each clone was determined through its ability to differentially damage two resistant and two susceptible wheat entries in two phases of screening. The first phase determined the damage responses of Russian wheat aphid wheat entries with resistance genes Dn4, Dn7, and susceptible ‘Custer’ to infestations by each clone to identify RWA1 to RWA4. The second phase used the responses of Custer and ‘Yuma’ wheat to identify RWA1 and RWA5. Only two biotypes, RWA1 and RWA2, were identified in this study. The biotype composition across all collection sites was 27.2% RWA1 and 72.8% RWA2. RWA biotype frequency by state indicated that RWA2 was the predominant biotype and composed 73–95% of the biotype complex in Texas, Oklahoma, Colorado, and Wyoming. Our study indicated that RWA2 is widely distributed and that it has rapidly dominated the biotype complex in wheat and barley within its primary range from Texas to Wyoming. Wheat with the Dn4 resistance gene will have little value in managing RWA in the United States, based on the predominance of RWA2. [ABSTRACT FROM AUTHOR]

The Russian wheat aphid, Diuraphis noxia (Mordvilko) (Homoptera: Aphididae), has been a major economic pest of small grains in the western United States since its introduction in 1986. Recently, a new Russian wheat aphid biotype was discovered in southeastern Colorado that damaged previously resistant wheat, Triticum aestivum L. Biotype development jeopardizes the durability of plant resistance, which has been a cornerstone for Russian wheat aphid management. Our objective was to assess the relative amount of biotypic diversity among Russian wheat aphid populations collected from cultivated wheat and barley, Hordeum vulgare L. We conducted field surveys from May through June 2002 and August 2003 from seven counties within Texas, Kansas, Nebraska, and Wyoming. Based upon a foliar chlorosis damage rating, three new Russian wheat aphid biotypes were identified, one of which was virulent to all characterized sources of Russian wheat aphid resistance. The future success of Russian wheat aphid resistance breeding programs will depend upon the continual monitoring of extant biotypic diversity and determination of the ecological and genetic factors underlying the development of Russian wheat aphid biotypes. [ABSTRACT FROM AUTHOR]