Russian Wheat Aphid Populations Research Articles

Seed rates and insecticides effects on Russian wheat aphid Diuraphis noxia (Hemiptera: Aphididae) occurrence in irrigated durum wheat (Triticum durum) in the central highland of Ethiopia

The Russian Wheat Aphid (RWA) Diuraphis noxia (Kurdjumov) causes severe damage to wheat in the highlands of Ethiopia. An experiment was conducted to evaluate the effect of seed rates and insecticides on incidence of RWA and grain yield of durum wheat under irrigated filed condition at Debre Zeit Agricultural Research Center, Ethiopia, during 2017. Three insecticides (Dimethoate 40 EC, Actellic 50 EC and Highpro220EW) and one untreated check with six seed rates (75,100,125, 150,175, and 200 kg/ha) were used in split plot design with three replications. Data were collected on plant or plot basis. Data on RWA number was recorded on plant bases. Whereas, leaf rolling, chlorosis, number of deformed head, phenological stages, yield and other yield related parameters were collected on plot basis. Data were subjected to analysis of variance using SAS version 9.3. Mean separation was made using least significant test using Tukey’s HSD (Honestly Significant Difference). The seed rates and insecticides significantly affected the incidence of RWA plant damage (chlorosis), deformed heads, plant height, yield and yield components except the interaction for number of grains per head and thousand seed weight. Dimethoate 40EC and Highpro 220EW sprayed plots gave the highest grain yield and the tallest plant height. The highest grain yield was obtained from 125 kg/ha sown plots and sprayed with Dimethoate 40 EC and the lowest grain yield was obtained from the untreated check sown at the rate of 75 kg/ha. The highest number of RWA per tiller and damaged plants were recorded on the untreated plots and the lowest RWA numbers was recorded, in decreasing order, from Dimethoate 40EC, Highpro 220EW and Actilic 50EC treated plots. Untreated plots with seed rate 150 kg/ha, 175 kg/ha and 200 kg/ha sown plots significantly reduced RWA population than the others. This indicates that there is the possibility of using seed rates above 150 kg/ha to managing RWA. RWA is a serious pest of irrigated wheat in Ethiopia, causing substantial yield losses in different seasons to in irrigated wheat production. The overall results indicated that sowing at a seed rates of 125 kg/ha and spraying Dimethoate 40EC gave the highest yield grain and can be recommended for RWA management under irrigated condition.

Reproduction and Population Dynamics as Biotypic Markers of Russian Wheat Aphid Diuraphis noxia (Kurdjumov).

Russian wheat aphid Diuraphis noxia (Kurdjumov) is widely established in wheat-growing countries where it causes significant economic losses. The development and use of Russian wheat aphid (RWA)-resistant wheat varieties has been constrained by the variation in resident RWA populations and the evolution of virulent biotypes. An experiment was set up at the Kenya Agricultural and Livestock Research Organization (KALRO), Njoro, to characterize RWA populations based on phenotypic characteristics of reproduction, development and population dynamics. RWA populations from the regions of Eldoret, Mau Narok and Njoro were used in the study. A factorial experiment was set up in randomized complete block design replicated eleven times. A single day-old nymph was placed on a new, fully-open leaf in a 0.5 cm-diameter clear plastic straw leaf cage and observed daily for its entire lifetime. The results showed that there were variations in aphid lifespan, reproductive longevity and aphid fecundity between populations, indicating that the phenotypic markers used to determine biotypes were good enough to show distinct biotypes among populations of the RWA in Kenya. Further, the study concluded that the use of phenotypic life and reproductive markers was a valid way of characterizing biotypes of RWA worldwide.

Changes in the Russian Wheat Aphid (Hemiptera: Aphididae) Biotype Complex in South Africa.

Russian wheat aphid Diuraphis noxia (Kurdjumov) has spread from its native area in central Asia to all the major wheat-producing countries in the world to become an international wheat pest. Because the Russian wheat aphid is a serious threat to the wheat industry in South Africa, it is important to investigate the key factors involved in the distribution of Russian wheat aphid biotypes and in the changes of the Russian wheat aphid biotype complex in South Africa. There are currently four known Russian wheat aphid biotypes occurring in South Africa. Russian wheat aphid samples were collected from 2011 to 2014 during the wheat-growing season in spring and summer and these samples were screened to determine the biotype status. RWASA1 occurred predominantly in the Western Cape, while RWASA2 and RWASA3 occurred predominantly in the Eastern Free State. Following the first record of RWASA4 in 2011, this biotype was restricted to the Eastern Free State. The surveys suggest that the Russian wheat aphid bioype complex was more diverse in the Eastern Free State than in the other wheat production areas. There was also a shift in Russian wheat aphid biotype composition over time. The Russian wheat aphid biotype complex is dynamic, influenced by environmental factors such as host plants, altitude, and climate, and it can change and diversify over time causing fluctuation in populations over sites and years. This dynamic nature of the Russian wheat aphid will continue to challenge the development of Russian wheat aphid-resistant wheat cultivars in South Africa, and the continued monitoring of the biotypic and genetic structure, to determine genetic relatedness and variation in different biotypes, of Russian wheat aphid populations is important for protecting wheat.

Change in Biotypic Diversity of Russian Wheat Aphid (Hemiptera: Aphididae) Populations in the United States

A key component of Russian wheat aphid, Diuraphis noxia (Kurdjumov), management has been through planting resistant wheat cultivars. A new biotype, RWA2, appeared in 2003 which caused widespread damage to wheat cultivars containing the Dn4 gene. Biotypic diversity in Russian wheat aphid populations has not been addressed since 2005 when RWA2 dominated the biotype complex. Our objectives were to determine the biotypic diversity in the Central Great Plains and Colorado Plateau at regional (2010, 2011, 2013) and local (2012) levels and detect the presence of new Russian wheat aphid biotypes. Regional and within-field aphid collections were screened against Russian wheat aphid-resistant wheat genotypes containing genes Dn3, Dn4, Dn6, Dn7, Dn9, CI2401; and resistant barley STARS 9301B. In 2010, all aphid collections from Texas were avirulent to the Dn4 resistance gene in wheat. Regional results revealed Dn4 avirulent RWA6 was widespread (55-84%) in populations infesting wheat in both regions. Biotypes RWA1, 2, and 3/7 were equally represented with percentages<20% each while RWA8 was rarely detected. Combining percentages of RWA1, 6, and 8 across regions to estimate avirulence to Dn4 gene revealed high percentages for both 2011 (64-80%) and 2013 (69-90%). In contrast, the biotype structure at the local level differed where biotype percentages varied up to ≥2-fold between fields. No new biotypes were detected; therefore, Dn7, CI2401, and STARS9301B remained resistant to all known Russian wheat aphid biotypes. This study documents a shift to Dn4 avirulent biotypes and serves as a valuable baseline for biotypic diversity in Russian wheat aphid populations prior to the deployment of new Russian wheat aphid-resistant wheat cultivars.

Occurrence of, and yield response to, Russian wheat aphid, Diuraphis noxia (Hemiptera: Aphididae) in irrigated wheat in Ethiopia

The present study investigated the incidence and effect of the Russian wheat aphid (RWA) Diuraphis noxia (Kurdjumov) on irrigated wheat yield at Debre Zeit, Ethiopia. Wheat varieties were sown at the rate of 140 kg/ha on Vertisols on plots of 3 × 3m. Treatments were tested in a split plot with varieties as the subplot and insecticide as the main plot, and were replicated three times. RWA appeared first when the crop reached the four- to five-leaf stage (Zadoks stage 22). In 2012 season, the RWA population peaked in the last week of March, and at this peak infestation, the average number of RWA per tiller was 46.9 on Denbi, 59.6 on Kubsa, 63.6 on Millennium and 56.2 on Werer. However, there were less than three RWA per tiller on sprayed wheat. In 2013, at the peak population intensity, there were 10.1, 10.5, 9.6 and 10.2 RWA per tiller on Denbi, Kubsa, Millennium and Werer, respectively. However, on sprayed wheat, the average population was less than one per tiller. The pattern of population build-up observed in the 2014 season was similar to that in 2013. Natural enemies of RWAwere only a few generalist predators and were found at an extremely low density. In the 2012 season, avoidable loss in plant height, seed weight, grain number and grain yield ranged from 3 to 10%, 32 to 47%, 12 to 25%, and 69 to 93%, respectively. In the 2013 season, avoidable loss in seed weight and grain yield varied between 14 and 20%, and 15 and 41%, respectively. Similarly, in the 2014 season, avoidable loss in seed weight ranged between 9 and 24% and in grain yield between 35 and 49%.

Effects of Planting Date and Barley Variety on Russian Wheat Aphid (Hemiptera: Aphididae) Populations in Colorado, Kansas, and Nebraska.

The Russian wheat aphid, Diuraphis noxia (Kurdjumov) (Hemiptera: Aphididae), is an important pest in the western Great Plains of the United States, where it causes hundreds of millions of dollars of losses to barley and wheat production through reduced yields. Experiments to evaluate the effect of early planting and resistance in barley (Hordeum vulgare L.) on D. noxia were conducted at Fort Collins, CO; Tribune, KS; and Sidney, NE, in 2007, 2008, and 2009. Treatments included two planting dates and four cultivars, the D. noxia-resistant barley cultivars 'Stoneham' (Otis*4/STARS 9577B) and 'Sidney' (Otis*4/STARS 9301B), the susceptible cultivar 'Otis', and Otis treated with thiamethoxam. In tiller samples collected from May through early July, consistently lower D. noxia populations were found in plots planted ≍30 d earlier than normal at Fort Collins in all three years, and at Tribune in 2007. With one location-year exception, lower D. noxia populations occurred on plants of resistant varieties or the susceptible variety Otis treated with thiamethoxam than on untreated Otis plants. There were no significant differences in D. noxia populations produced on plants of either resistant variety and susceptible Otis plants treated with thiamethoxam. Interactions between resistant varieties and early planting resulted in reduced D. noxia populations at Fort Collins in 2007 and 2009, and at Tribune and Sidney in 2007. Planting D. noxia-resistant barley varieties, planting varieties earlier than normal, and the synergistic effect of resistant variety and early planting can significantly reduce D. noxia infestations on barley in the western High Plains.

Variation between Ethiopian and North American Barley Varieties (Hordeum vulgare) in Response to Russian Wheat Aphid (Diuraphis noxia) populations

The Russian wheat aphid, Diuraphis noxia (Mordvilko) (Hemiptera: Aphididae), causes severe damage to barley, Hordeum vulgare L. (Poales: Poaceae), in the highlands of Ethiopia. Little information is available on the control of this pest in Ethiopia. An experiment aimed at evaluating the resistance of barley varieties from the USA to D. noxia populations and determining biotypic variation between Ethiopian and North American D. noxia populations was conducted. The D. noxia-resistant barley varieties Burton and RWA-1758 from the USA, the resistant barley line 3296-15 from Ethiopia, and a local Ethiopian susceptible variety were included in a randomized design in a greenhouse under natural light conditions. There were highly significant differences (P < 0.001) in the mean D. noxia population, leaf chlorosis, leaf rolling, plant stunting, number of tillers per plant, and the percentage of infested tillers per plant between the resistant and susceptible varieties. The aphid population per tiller was lower on the resistant barley plants than on the susceptible plants. Severe plant damage was observed on the local barley variety, while the least damage was observed on Burton, followed by RWA-1758. Burton and RWA-1758 were therefore highly resistant and moderately resistant, respectively, to the northern Ethiopian D. noxia populations, indicating similarities in biotypes between the United States and northern Ethiopian D. noxia populations. The damage to variety 3296-15 was greater than to Burton and RWA-1758. Leaf chlorosis scores and leaf rolling scores for variety 3296-15 upon treatment with the north Ethiopian D. noxia population indicate likely biotypic variation between D. noxia populations of northern and central Ethiopia.

Variation between Ethiopian and North American barley varieties (Hordeum vulgare) in response to Russian wheat aphid (Diuraphis noxia) populations.

The Russian wheat aphid, Diuraphis noxia (Mordvilko) (Hemiptera: Aphididae), causes severe damage to barley, Hordeum vulgare L. (Poales: Poaceae), in the highlands of Ethiopia. Little information is available on the control of this pest in Ethiopia. An experiment aimed at evaluating the resistance of barley varieties from the USA to D. noxia populations and determining biotypic variation between Ethiopian and North American D. noxia populations was conducted. The D. noxia -resistant barley varieties Burton and RWA-1758 from the USA, the resistant barley line 3296-15 from Ethiopia, and a local Ethiopian susceptible variety were included in a randomized design in a greenhouse under natural light conditions. There were highly significant differences ( P < 0.001) in the mean D. noxia population, leaf chlorosis, leaf rolling, plant stunting, number of tillers per plant, and the percentage of infested tillers per plant between the resistant and susceptible varieties. The aphid population per tiller was lower on the resistant barley plants than on the susceptible plants. Severe plant damage was observed on the local barley variety, while the least damage was observed on Burton, followed by RWA-1758. Burton and RWA-1758 were therefore highly resistant and moderately resistant, respectively, to the northern Ethiopian D. noxia populations, indicating similarities in biotypes between the United States and northern Ethiopian D. noxia populations. The damage to variety 3296-15 was greater than to Burton and RWA-1758. Leaf chlorosis scores and leaf rolling scores for variety 3296-15 upon treatment with the north Ethiopian D. noxia population indicate likely biotypic variation between D. noxia populations of northern and central Ethiopia.

Cyclical Parthenogenetic Reproduction in the Russian Wheat Aphid (Hemiptera: Aphididae) in the United States: Sexual Reproduction and Its Outcome on Biotypic Diversity

In 1986, the Russian wheat aphid, Diuraphis noxia (Kurdjumov) (Hemiptera: Aphididae), became an invasive species of United States. Nearly 20 yr later, new biotypes appeared that were capable of overcoming most sources of resistance and became a renewed threat to wheat, Triticum aestivum L., production. Cyclical (CP) and obligate (OP) parthenogenesis enables aphids to both adapt to changing environments and exploit host resources. We documented these forms of reproduction for Russian wheat aphid in wheat and wild grasses in the Central Great Plains and Rocky Mountain regions during falls 2004-2009. Colonies from sample sites also were held under unheated greenhouse conditions and observed for the presence of sexual morphs and eggs through the winter. Russian wheat aphid populations were mainly OP and attempted to overwinter as adults, regardless of region sampled. A few populations contained oviparae but no males (gynocyclic) and were not specific to any particular region. Observation of the Russian wheat aphid colonies under greenhouse conditions failed to produce males or eggs. In spring 2007, CP was confirmed in a small population of Russian wheat aphid that eclosed from eggs (fundatricies) on wild grasses and wheat near Dove Creek, CO, in the Colorado Plateau region where other aphid species undergo CP. Lineages from ninety-three fundatricies were screened against 16 resistant and susceptible cereal entries to determine their biotypic classification. A high degree of biotypic diversity (41.4%) was detected in this population. Although CP was a rare in Russian wheat aphid populations, genetic recombination during the sexual cycle creates new biotypes and can have significant effects on population genetics.

Russian wheat aphids (Diuraphis noxia) in China: native range expansion or recent introduction?

In this study, we explore the population genetics of the Russian wheat aphid (RWA) (Diuraphis noxia), one of the world's most invasive agricultural pests, in north-western China. We have analysed the data of 10 microsatellite loci and mitochondrial sequences from 27 populations sampled over 2 years in China. The results confirm that the RWAs are holocyclic in China with high genetic diversity indicating widespread sexual reproduction. Distinct differences in microsatellite genetic diversity and distribution revealed clear geographic isolation between RWA populations in northern and southern Xinjiang, China, with gene flow interrupted across extensive desert regions. Despite frequent grain transportation from north to south in this region, little evidence for RWA translocation as a result of human agricultural activities was found. Consequently, frequent gene flow among northern populations most likely resulted from natural dispersal, potentially facilitated by wind currents. We also found evidence for the long-term existence and expansion of RWAs in China, despite local opinion that it is an exotic species only present in China since 1975. Our estimated date of RWA expansion throughout China coincides with the debut of wheat domestication and cultivation practices in western Asia in the Holocene. We conclude that western China represents the limit of the far eastern native range of this species. This study is the most comprehensive molecular genetic investigation of the RWA in its native range undertaken to date and provides valuable insights into the history of the association of this aphid with domesticated cereals and wild grasses.

Distribution and Diversity of Russian Wheat Aphid (Hemiptera: Aphididae) Biotypes in South Africa and Lesotho

Russian wheat aphid, Diuraphis noxia (Kurdjumov) (Hemiptera: Aphididae) was recorded for the first time in South Africa in 1978. In 2005, a second biotype, RWASA2, emerged, and here we report on the emergence of yet another biotype, found for the first time in 2009. The discovery of new Russian wheat aphid biotypes is a significant challenge to the wheat, Triticum aestivum L., industry in South Africa. Russian wheat aphid resistance in wheat, that offered wheat producers a long-term solution to Russian wheat aphid control, may no longer be effective in areas where the new biotypes occur. It is therefore critical to determine the diversity and extent of distribution of biotypes in South Africa to successfully deploy Russian wheat aphid resistance in wheat. Screening of 96 Russian wheat aphid clones resulted in identification of three Russian wheat aphid biotypes. Infestations of RWASA1 caused susceptible damage symptoms only in wheat entries containing the Dn3 gene. Infestations of RWASA2 caused susceptible damage symptoms in wheat entries containing Dn1, Dn2, Dn3, and Dn9 resistant genes. Based on the damage-rating scores for the seven resistance sources, a new biotype, which caused damage rating scores different from those for RWASA1 and RWASA2, was evident among the Russian wheat aphid populations tested. This new biotype is virulent to the same resistance sources as RWASA2 (Dn1, Dn2, Dn3, and Dn9), but it also has added virulence to Dn4, whereas RWASA2 is avirulent to this resistance source.

Aphid feeding activates expression of a transcriptome of oxylipin-based defense signals in wheat involved in resistance to herbivory.

Damage by the Russian wheat aphid (RWA), Diuraphis noxia, significantly reduces wheat and barley yields worldwide. In compatible interactions, virulent RWA populations flourish and susceptible plants suffer extensive leaf chlorophyll loss. In incompatible interactions, RWA reproduction and population growth are significantly reduced and RWA-related chlorophyll loss in resistant plants is minor. The objectives of this study were to develop an understanding of the molecular and phytochemical bases of RWA resistance in plants containing the Dnx resistance gene. Microarray, real-time polymerase chain reaction, and phytohormone assays were conducted to identify transcriptome components unique to RWA-infested Dnx plants and susceptible (Dn0) plants, and to identify and characterize putative genes involved in Dnx plant defense responses. We found that RWA-infested Dnx plants upregulated >180 genes related to reactive oxygen species, signaling, pathogen defense, and arthropod allelochemical and physical defense. The expression of several of these genes in RWA-infested Dnx plants increased significantly from 6- to 24-h post infestation (hpi), but their expression in Dn0 plants, when present, was delayed until 48- to 96 hpi. Concentrations of 16- and 18-carbon fatty acids, trans-methyl-12-oxophytodienoic acid, and abscisic acid were significantly greater in Dnx foliage than in Dn0 foliage after RWA infestation, suggesting that Dnx RWA defense and resistance genes may be regulated via the oxylipin pathway. These findings provide a foundation for the elucidation of the molecular basis for compatible- and incompatible plant-aphid interactions.

Seasonal Presence of the Russian Wheat Aphid (Hemiptera: Aphididae) on Alternate Hosts in Colorado

Abstract. Russian wheat aphid populations have been monitored for the development of biotypes since the pest first appeared in the United States. Recent studies have confirmed the presence of five unique Russian wheat aphid biotypes in Colorado (Haley et al. 2004, Weiland et al. 2008), two of which were found on noncultivated grass hosts. The objective of this study was to confirm that while the Russian wheat aphid has undergone many changes as a species, the important grass hosts have not changed and are consistent each season. Species of noncultivated grass hosts were inventoried at field sites in four Colorado counties, Baca County, Montezuma County, Washington County, and Weld County, and the presence of Russian wheat aphids on the identified hosts was documented. Field sites were sampled in spring and fall 2005–2006 and the number and species of grass hosts were recorded and compared to look at host consistency across different geographic locations. Twenty-three grass species were identified across a...

An approach to the nonlinear dynamics of Russian wheat aphid population growth with the cusp catastrophe model

AbstractMany insect field populations, especially aphids, often exhibit irregular and even catastrophic fluctuations. The objective of the present study is to explore whether or not the population intrinsic rates of growth (rm) obtained under laboratory conditions can shed some light on the irregular changes of insect field populations. We propose to use the catastrophe theory, one of the earliest nonlinear dynamics theories, to answer the question. To collect the necessary data, we conducted a laboratory experiment to investigate population growth of the Russian wheat aphid (RWA), Diuraphis noxia (Mordvilko), in growth chambers. The experiment was designed as the factorial combinations of five temperatures and five host plant‐growth stages (25 treatments in total): 1800 newly born RWA nymphs arranged in the 25 treatments (each treatment with 72 repetitions) were observed for their development, reproduction and survival through their entire lifetimes. After obtaining the population intrinsic rates of growth (rm) from the experimental data under various environmental conditions, we built a cusp catastrophe model for RWA population growth by utilizing rm as the system state variable, and temperature and host plant‐growth stage as control variables. The cusp catastrophe model suggests that RWA population growth is intrinsically catastrophic, and dramatic jumps from one state to another might occur even if the temperature and plant‐growth stage change smoothly. Other basic behaviors of the cusp catastrophe model, such as catastrophic jumps, hystersis and divergence, are also expected in RWA populations. These results suggest that the answer to the previously proposed question should be “yes”.

A survival-analysis-based simulation model for Russian wheat aphid population dynamics

A simulation model for Russian wheat aphid (RWA), Diuraphis noxia (Mordvilko), populations is built by integrating survival-analysis-based development and survivor functions and the same-shape reproduction distribution model in the framework of Leslie [Leslie, P.H., 1945. On the use of matrices in certain population mathematics. Biometrika 33, 183–212] matrix structure. Survival analysis is utilized to model both the development and survival of RWA populations, and the Cox (1972) proportional hazards model is fitted with the data sets from our laboratory observation of 1800 RWA individuals under 25 factorial combinations of five temperature regimes and five barley plant-growth stages. Rather than using simple age-specific survivor rates as in the traditional Leslie matrix, the survivor functions based on survival analysis describe age-specific, temperature and plant stage-dependent RWA survival probabilities. Similarly, a probability model from survival analysis to estimate the probability that an individual will reach mature adult stage is utilized to describe the development process; this makes the transition from nymphal stage to mature adult stage dependent on RWA age as well as temperature and plant-growth stage. Inspired by the same-shape distribution and rate-summation approach for modeling insect development, a similar approach for modeling insect reproduction under variable temperature is developed. This new same-shape reproduction distribution model incorporates individual variation in reproduction capability, as well as the effects of RWA age, temperature and plant-growth stage. Consequently, the same-shape reproduction distribution model replaces the simple age-specific fecundities in Leslie matrix model. To the best of our knowledge, this work is the first to introduce survival analysis to simulation modeling in entomology and ecology and also the first to integrate our newly developed same-shape reproduction distribution model into application.

Biotypic Diversity in Colorado Russian Wheat Aphid (Hemiptera: Aphididae) Populations

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' (Dn1), '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.

Biotypic Diversity in Colorado Russian Wheat Aphid (Hemiptera: Aphididae) Populations

Biotypic Diversity in Colorado Russian Wheat Aphid (Hemiptera: Aphididae) Populations

Absence of Mitochondrial DNA Sequence Variation in Russian Wheat Aphid (Hemiptera: Aphididae) Populations Consistent with a Single Introduction into the United States

Russian wheat aphid, Diuraphis noxia (Kurdjumov), was introduced into North America in Mexico during 1980 and by 1988 had spread north across the Western US into Southern Canada. South Africa has been suspected as the source of the introduction. Russian wheat aphid is the major insect pest of wheat and barley in the southern and central plains states. Resistant wheat with the Dn4 gene was the primary management tactic from 1996 to 2003. During 2003, a biotype able to injure Dn4 wheat (designated RWA2) appeared in Colorado. The source of the biotype is unclear, that is whether it represents a new introduction from another country or if it arose from the extant population in the US. We examined a 332 bp portion of the cytochrome oxidase subunit I gene (COI) in the mtDNA of Russian wheat aphid collected in the US from 1986 through 2006. Also included were specimens from Mexico and South Africa. Except for two nucleotides in two individual aphids, no COI sequence variation was found in US populations over a 20 yr period. US populations had COI sequences which were identical to those found in Mexico, Turkey, France, and one aphid from South Africa. A second aphid from South Africa differed by only two bp. The lack of COI nucleotide variation suggested that biotype RWA2 did not represent a second introduction of a genetically distinct population from another country. The data are consistent with a single introduction from South Africa and no other introductions of virulent biotypes into the US occurred since 1986.

Biotypic and Genetic Variation Within Tropical Populations of Russian Wheat Aphid, Diuraphis noxia (Kurdjumov) (Homoptera: Aphididae) in Kenya

Biotypic and Genetic Variation Within Tropical Populations of Russian Wheat Aphid, Diuraphis noxia (Kurdjumov) (Homoptera: Aphididae) in Kenya

Response of Resistant and Susceptible Barley to Infestations of Five Diuraphis noxia (Homoptera: Aphididae) Biotypes

Since 2003, four new biotypes of the Russian wheat aphid, Diuraphis noxia (Kurdjumov) (Homoptera: Aphididae), RWA2-RWA5, have been discovered that have the ability to damage most of the wheat germplasm resistant to the original Russian wheat aphid population (RWA1). Barley germplasm lines with resistance to RWA1 have not yet been evaluated against the newest biotypes. Our study compared how biotypes RWA1-RWA5 affected the growth and leaf damage of RWA1-resistant germplasm (STARS 9301B, STARS 9577B), moderately resistant germplasm (MR-015), and susceptible varieties (Schuyler, Harrington, and Morex) under greenhouse conditions. Russian wheat aphid population levels also were determined 14 d after plant infestation. STARS 9301B exhibited strong resistance by showing only small differences in leaf damage and growth parameters from the feeding by the biotypes. STARS 9577B showed greater differences in damage by the Russian wheat aphid biotypes than STARS 9301B, yet, the ratings were still within the resistant category (e.g., chlorosis rating 2.3-4.9). Leaf chlorosis ratings for MR-015 ranged from 5.0 to 6.9 and fell within the moderately resistant to susceptible categories for all the biotypes. The greatest difference in leaf chlorosis occurred in Morex where RWA2 showed less virulence than the other biotypes. Feeding by the Russian wheat aphid biotypes produced only small differences in leaf rolling and plant growth within plant entries. Population levels of the Russian wheat aphid biotypes did not differ within barley entries (n = 610-971) at the termination of the study (14 d). From our research, we conclude that the new Russian wheat aphid biotypes pose no serious threat to the key sources of resistance in barley (STARS 9301B and 9577B).