Arthropod-Plant Interactions

, Volume 6, Issue 1, pp 67–73

Russian wheat aphid (Hemiptera: Aphididae) reproduction and development on five noncultivated grass hosts

Authors

  • Sherri F. Pucherelli
    • Department of Bioagricultural Sciences and Pest ManagementColorado State University
  • Frank B. Peairs
    • Department of Bioagricultural Sciences and Pest ManagementColorado State University
    • Department of Bioagricultural Sciences and Pest ManagementColorado State University
  • Terri L. Randolph
    • Department of Bioagricultural Sciences and Pest ManagementColorado State University
Original Paper

DOI: 10.1007/s11829-011-9152-5

Cite this article as:
Pucherelli, S.F., Peairs, F.B., Merrill, S.C. et al. Arthropod-Plant Interactions (2012) 6: 67. doi:10.1007/s11829-011-9152-5

Abstract

The Russian wheat aphid, Diuraphis noxia (Kurdjumov), is a small grains pest of worldwide economic importance. The Russian wheat aphid is polyphagous and may encounter differential selective pressures from noncultivated grass hosts. Aphid biotypic diversity can disrupt the progress of plant breeding programs, leading to a decreased ability to manage this pest. The goal of this research was to quantify Russian wheat aphid biotype 2 (RWA2) reproductive and development rates on five common noncultivated grass hosts to gain information about host quality, potential refuges, and sources of selection pressure. First, RWA2 reproduction was compared on crested wheatgrass (Agropyron cristatum, (L.) Gaertn.), intermediate wheatgrass (Elytrigia intermedia, (Host) Nevski), slender wheatgrass (Elymus trachycaulus, (Link) Gould ex Shinners), western wheatgrass (Pascopyrum smithi, (Rydb.) A. Löve), and foxtail barley (Hordeum jubatum, (L.) Tesky) at 18–24°C. Second, RWA2 reproduction was compared on intermediate and crested wheatgrass at three temperature regimes 13–18°C, 18–24°C, and 24–29°C. At moderate temperatures (18–24°C), the intrinsic rate of increase values for all five hosts ranged from 0.141 to 0.199, indicating the possibility for strong population sources on all tested hosts. Aphids feeding on crested and intermediate wheatgrass at the 13–18°C temperature had lower fecundity, less nymph production days, longer generational times, and lower intrinsic rate of increase than aphids feeding at the 18–24°C temperature regime. Aphids feeding at 24–29°C did not survive long enough to reproduce. The positive intrinsic rates of increase in Russian wheat aphid on the wheatgrasses suggest that these grasses can support aphid populations at moderate to low temperatures.

Keywords

Russian wheat aphidNoncultivated hostsReproductionDevelopmentTemperature

Introduction

The Russian wheat aphid, Diuraphis noxia (Kurdjumov), is a small grains pest and is considered one of the most economically damaging pests of wheat worldwide (Morrison and Peairs 1998). Development of resistant cultivars has been one of the most successful techniques for the management of Russian wheat aphid. The presence of Russian wheat aphid biotypic diversity can disrupt the progress of plant breeding programs. For example, a new Russian wheat aphid biotype (designated as RWA2) was discovered in Colorado in 2003. This new biotype is virulent to many advanced wheat lines, which were developed to manage RWA1 within the United Stated and Canada (Haley et al. 2004). Selective pressures such as antibiosis and antixenosis expressed by resistant cultivars and noncultivated grass hosts may help explain observed biotypic variation. Porter et al. (1997) studied greenbug, Schizaphis graminum (Rondani), biotype development and suggested that noncultivated grass hosts could be a reservoir for aphid biotypes. Since this theory was suggested, several unique greenbug biotypes have been found on noncultivated hosts (Anstead et al. 2003, Burd and Porter 2006). Similarly, Weiland et al. (2008) found two new Russian wheat aphid biotypes on noncultivated grasses. Porter et al. (1997) suggested that noncultivated hosts play an important role in maintaining aphid genetic diversity and that exposure to selective pressures on grasses provides incentive for additional diversity, possibly leading to biotypes adapted to exploit resistant cultivars.

The Russian wheat aphid is polyphagous, feeding on winter wheat and barley during the winter and spring and surviving on noncultivated grass hosts during the summer months (Burd et al. 1998). It is still unclear which cool season grass species are suitable hosts for the Russian wheat aphid and whether large differences in suitability exist among species (Donahue et al. 2000). Alternative host suitability can be quantified using growth rate parameters, such as the intrinsic rate of increase. The intrinsic rate of increase calculation is composed of factors which contribute to population growth, including net reproductive rate, immature development rates, and generation time. An aphid’s intrinsic rate of increase is influenced by plant growth stage and quality, temperature, moisture, aphid biotype, and feeding site (Girma et al. 1990). Typically, selection pressure increases with decreasing host quality, so determining host quality can help assess potential refuges and sources of selection pressure (Merrill et al. 2008). Furthermore, changes in an aphid’s intrinsic rate of increase could result in expanded geographic range or altered distribution (Randolph et al. 2008).

Noncultivated grasses may provide selective pressures and resistance by means of antibiosis or antixenosis. Antixenosis is expressed differently in plants with variation in leaf trichome size, leaf epicuticular structure, or tiller density. For example, western and intermediate wheatgrass have strongly ribbed leaves covered with a waxy powder. Grasses with reddish colored leaves, such as crested and slender wheatgrass, may be antixenotic during the host selection process (Ni and Quisenberry 1997). Antibiosis, where toxins are expressed by the plant to suppress or kill insects feeding on them, may be more prevalent in grasses than in cultivated wheat.

Noncultivated grass hosts provide the Russian wheat aphid with summer refuges, but grasses at lower elevations often have senesced by midsummer, so aphids may seek grasses at higher elevations that are still in vegetative and early reproductive stages. Russian wheat aphids have been found on eighteen different grass species at all elevations between 1,524 m and 3,048 m in Colorado (Randolph et al. 2011). Therefore, grasses found in montane environments may affect aphid phenology.

The first objective of this study was to determine Russian wheat aphid reproductive and development rates on five noncultivated grass hosts commonly utilized by Russian wheat aphids in Colorado montane environments (Randolph et al. 2011). These hosts included crested wheatgrass (Agropyron cristatum, (L.) Gaertn.), intermediate wheatgrass (Elytrigia intermedia, (Host) Nevski), slender wheatgrass (Elymus trachycaulus, (Link) Gould ex Shinners), western wheatgrass (Pascopyrum smithi, (Rydb.) A. Löve), and foxtail barley (Hordeum jubatum, (L.) Tesky). The second objective was to compare Russian wheat aphid reproduction and development under high, moderate, and low temperature regimes on intermediate and crested wheatgrass. Understanding the Russian wheat aphid’s population dynamics on these common alternative hosts can help elucidate host quality, potential refuges, and sources of selection pressure.

Methods

Two separate intrinsic rate of increase experiments were conducted under three different temperature regimes. Hosts used for these experiments included intermediate wheatgrass (“Oahe,” Sharp Brothers Seed Company, Healy, Kansas), crested wheatgrass (“Hycrest,” Sharp Brothers Seed Company, Healy, Kansas), western wheatgrass (“Native,” Pawnee Buttes Seed Inc. Greeley, Colorado), slender wheatgrass (“San Luis,” Pawnee Buttes Seed Inc. Greeley, Colorado), and foxtail barley (unknown variety, seed collected on the Colorado State University campus). Seeds were germinated in Petri dishes lined with moistened disc style coffee filters. Seeds were planted in 13 cm pots containing three parts soil, two parts peat moss potting soil mixture, and one part perlite. Grasses were grown in a greenhouse and covered with organza sleeve cages to protect them from natural infestation and predation. All grasses used in this experiment were 2–6 months of age; Feekes stages 2–10.5 (tillering to heading). All experiments were performed in an Environmental Growth Chamber (Model G10, Environmental Growth Chambers, Chagrin Falls, OH) under the appropriately programmed temperature regime (13–18°C, 18–24°C, or 24–29°C) with a 14:10 (L/D) h photoperiod. Plants were watered every other day, or as needed. Experimentation began when eight pots of each plant species had matured to the same age and growth stage. One clip cage, similar to those described by Hawley et al. (2003), was placed on the youngest leaf on each of the eight plants. Three 3rd–4th instar RWA2, from the Colorado State University colony (aphids reared on a winter wheat varietal mixture), were placed in each cage. Aphids were moved in and out of the clip cages with a size 0000 sable/synthetic horsehair brush. The three aphids in each clip cage were monitored daily until two or three nymphs were born on the same day. At this time, all three original aphids were removed from the cage, leaving the newly born aphids. This date was recorded as the birth date of the aphid of interest. When these aphids reached approximately third instar all but one were removed. The remaining aphid became the aphid of interest. This process insured that the aphid of interest had completed her whole life cycle on the specific grass species to reduce maternal effects. The aphid of interest was monitored every 24 h for the duration of her life, and all aphids born to her were removed and recorded daily. When the aphid and clip cage had to be moved due to leaf senescence, they were moved to the youngest unrolled leaf on the same plant.

Our first experiment (Experiment 1) included five hosts (intermediate wheatgrass, crested wheatgrass, western wheatgrass, slender wheatgrass, and foxtail barley) and was conducted at a temperature regime of 18–24°C, which is the optimum temperature for reproduction according to Girma et al. (1990) and Randolph et al. (2008). These hosts were selected because they were observed to be common hosts for Russian wheat aphids in montane environments (Randolph et al. 2011).

Our second experiment (Experiment 2) examined two of the five hosts (intermediate and crested wheatgrass) using three temperature regimes: high (24–29°C), moderate (18–24°C), and low (13–18°C).

All statistical analysis was carried out using SAS v. 9.1, Proc GLM and Proc Mixed LSMeans (SAS Institute 2005). Nine life statistic parameters were calculated for each aphid of interest. Life statistics were recorded as described by Hawley et al. (2003) and included pre-nymphipositional period (the number of days until first birth), nymphipositional period (the days lapsed from first birth to last), number of nymphs produced per day of nymphipositional period, number of nymph production days (number of days on which the aphid of interest actually gave birth), maximum number of nymphs produced in a 24-h period, longevity (the days between birth and death), and fecundity (total nymphs produced). All fecundity data were transformed by the square root method prior to analysis, with original means reported in the results.

Mean generation time (G) was calculated as described by Behle and Michels (1990) using the following formula:
$$ G = \sum l_{x} m_{x} x/R_{o} $$
where lx is the probability of being alive on day x. lx was generated by first calculating the probability of death on each day. To calculate the probability of being alive on day x (lx), we used the probnorm function in SAS (SAS Institute 2005), where the input for probnorm function was calculated by subtracting day x by average longevity and dividing by the standard deviation of longevity, which resulted in the probability of death on each day. To find the probability of being alive on day x (lx), the probability of death was subtracted from one. The variable mx is the average birth rate on day x and was generated by averaging the births of all eight aphids of interest on a single day. The variable Ro is fecundity (i.e., total nymphs produced by each aphid of interest).
Mean generational time and intrinsic rate of increase (Birch 1948) were calculated using a fitted least mean square approach; therefore, statistics about the central tendencies of the means were not calculated. The intrinsic rate of increase (r) was calculated using the following formula:
$$ \sum e^{ - rx} \left( {l_{x} m_{x} } \right) = 1 $$
where x is the time increment (experimental day), lx is the probability of being alive on day x, mx is the average birth rate on day x, and r is the intrinsic rate of increase.

Results and discussion

Experiment 1

When comparing RWA2 reproduction and development on crested wheatgrass, intermediate wheatgrass, foxtail barley, slender wheatgrass, and western wheatgrass, reproductive differences were observed for most parameters (Table 1). Significant differences were not observed among hosts for pre-nymphipositional period (F = 0.78; df = 4; P = 0.5482) and number of nymphs produced per day of nymphipositional period (F = 1.92; df = 4; P = 0.1297).
Table 1

Reproduction and development of RWA2 on five noncultivated hosts at 18–24°C and 14:10 (L/D) photoperiod

Host

PNympP

NympP

NpDNP

NPD

Max

Longevity

Fecundity

Crested wheatgrass

12.1 ± 1.1a

34.3 ± 3.1a

1.2 ± 0.2a

23.9 ± 2.9a

3.4 ± 0.3a

48.8 ± 2.7a

42.3 ± 6.9a

Intermediate wheatgrass

9.5 ± 1.2a

33.4 ± 3.5ab

1.3 ± 0.3a

23.1 ± 3.7a

4.1 ± 0.9a

43.9 ± 3.0ab

46.6 ± 15.2a

Foxtail barley

11.0 ± 0.6a

24.1 ± 4.4bc

0.9 ± 0.1a

15.1 ± 2.7b

2.9 ± 0.4ab

41.9 ± 3.5ab

23.4 ± 4.8ab

Western wheatgrass

11.3 ± 1.1a

19.3 ± 2.4c

0.6 ± 0.1a

10.1 ± 1.5b

1.8 ± 0.3b

39.9 ± 2.1bc

12.5 ± 2.5b

Slender wheatgrass

11.4 ± 1.3a

18.3 ± 2.6c

1.1 ± 0.2a

12.0 ± 1.8b

2.8 ± 0.5ab

32.1 ± 3.6c

20.4 ± 4.3b

Means in the same column followed by the same letter are not statistically different from each other (α = 0.05; LSMeans). Fecundity data transformed by the square root method, original means presented

PNymP pre-nymphipositional period, NympP nymphipositional period, NpDNP number of nymphs produced per day of nymphipositional period, NPD number of nymph production days, Max maximal number of nymphs produced in a 24-h period

Differences in nymphipositional period were observed among the five hosts (F = 5.43; df = 4; P = 0.0017). Aphids feeding on crested wheatgrass had a longer nymphipositional period (34.3 ± 3.1 days) than those on foxtail barley (24.1 ± 4.4 days), slender wheatgrass (18.3 ± 2.6 days), and western wheatgrass (19.3 ± 2.4 days). Aphids on intermediate wheatgrass had a longer nymphipositional period (33.4 ± 3.5 days) than those on slender and western wheatgrass.

Aphids feeding on different hosts varied in the number of days on which nymph production occurred (F = 5.94; df = 4; P = 0.0009). Aphids on crested and intermediate wheatgrass had more nymph production days (23.9 ± 2.9 days and 23.1 ± 3.7 days, respectively) than those on foxtail barley (15.1 ± 2.7 days), western wheatgrass (10.1 ± 1.5 days), and slender wheatgrass (12.0 ± 1.8 days). Similarly, aphids on crested and intermediate wheatgrass hosts produced more nymphs in a 24-h period than aphids on western wheatgrass (F = 2.93; df = 4; P = 0.0342).

Aphid longevity on the five hosts was variable (F = 4.08; df = 4; P = 0.0081). Aphids feeding on crested wheatgrass lived longer (48.8 ± 2.7 days) than those on slender (32.1 ± 3.6 days) and western wheatgrass (39.9 ± 2.1 days). Also, aphids feeding on intermediate wheatgrass and foxtail barley lived longer than aphids on slender wheatgrass.

Aphid fecundity varied among hosts (F = 4.22; df = 4; P = 0.0068). Russian wheat aphids feeding on crested and intermediate wheatgrass produced more nymphs during their lifetime (42.3 ± 6.9 nymphs and 46.6 ± 15.2 nymphs, respectively) than aphids on western and slender wheatgrass (12.5 ± 2.5 nymphs and 20.4 ± 4.3 nymphs, respectively).

Mean generational time was calculated using a fitted least mean square approach; therefore, statistics about the central tendencies of the means were not calculated (Table 2). Mean generational time was longest for aphids feeding on crested wheatgrass (29.4 days), followed by intermediate wheatgrass (27.8 days), foxtail barley (23.9 days), western wheatgrass (21.0 days), and slender wheatgrass (19.9 days).
Table 2

Mean generation time and intrinsic rate of increase calculations for RWA2 on five noncultivated hosts at 18–24°C and 14:10 (L/D) photoperiod

Host

Mean generation time (days)

Intrinsic rate of increasea

Crested wheatgrass

29.4

0.170

Intermediate wheatgrass

27.8

0.199

Foxtail barley

23.9

0.166

Western wheatgrass

21.0

0.141

Slender wheatgrass

19.9

0.183

Mean generation time and intrinsic rate of increase values were fitted (i.e., optimized) using fitted least mean square approach; therefore, statistical information about the central tendencies of the means were not calculated

aIntrinsic rate of increase was calculated using methods developed by Birch (1948)

Intrinsic rate of increase calculations, as described by Birch (1948), do not allow for calculation of the central tendencies of the means (Table 2). Russian wheat aphids feeding on intermediate wheatgrass had the greatest intrinsic rate of increase (rm = 0.199), followed by slender wheatgrass (rm = 0.183), crested wheatgrass (rm = 0.170), foxtail barley (rm = 0.166), and western wheatgrass (rm = 0.141).

Russian wheat aphids feeding on crested wheatgrass, intermediate wheatgrass, and foxtail barley had longer nymphipositional periods, longevity, and greater fecundity than aphids feeding on slender and western wheatgrass. Since aphids on crested wheatgrass, intermediate wheatgrass, and foxtail barley had the longest generation times, their intrinsic rates of increase were lower. Typically, aphids that have shorter generation times have higher rates of increase because it takes less time to complete a generation. Aphids feeding on western and slender wheatgrass had relatively low fecundity, but their generation times were much faster than aphids feeding on the other three hosts. The low fecundity but short generation time resulted in intrinsic rates of increase similar to aphids with relatively higher fecundity and longer generation times.

Intrinsic rate of increase values is useful in determining host quality because they can quantify an aphid’s reproductive potential on a host. Typically, selection pressure increases with decreasing host quality, so quantifying host quality can help assess potential refuges and sources of selection pressure (Merrill et al. 2008).

At a temperature regime of 18–24°C, RWA2 had a positive intrinsic rate of increase on all five hosts tested, suggesting that each would support population growth under the moderate temperature regimes typical of the growing season in Colorado montane environments. The intrinsic rate of increase values calculated for these five noncultivated hosts is lower than those reported for wheat. For example, meta-analysis by Merrill et al. (2009) suggested that intrinsic rate of increase values on wheat would range between 0.21 and 0.3 for temperatures ranging from 18 to 24°C. Hence, because intrinsic rate of increase values is lower on alternate hosts tested in this study, it is likely that greater selection pressure exists for aphids feeding on these alternate hosts than on wheat.

Experiment 2

Temperature regime changes resulted in RWA2 reproduction and development differences between crested and intermediate wheatgrasses (Table 3).
Table 3

Reproduction and development data for RWA2 on crested and intermediate wheatgrass at 13–18°C, 18–24°C, and 24–29°C at 14:10 (L/D) photoperiod

Test parameter

Crested wheatgrass

Intermediate wheatgrass

13–18°C

18–24°C

24–29°Ca

13–18°C

18–24°C

24–29°Ca

PNympP

17.3 ± 2.3ab

12.1 ± 1.1b

_

22.5 ± 5.2a

9.5 ± 1.2b

_

NymP

32.6 ± 6.5ab

34.3 ± 3.1a

_

17.6 ± 7.3b

33.4 ± 3.5ab

_

NpDNP

1.2 ± 0.5ab

1.2 ± 0.2a

_

0.4 ± 0.1b

1.3 ± 0.3a

_

NPD

13.4 ± 2.3b

23.9 ± 2.7a

_

5.9 ± 2.5b

23.1 ± 3.7 a

_

Max

3.0 ± 0a

3.4 ± 0.3a

_

1.4 ± 0.4b

4.1 ± 0.9a

_

Longevity

45.9 ± 6.2a

48.8 ± 2.7a

_

44.0 ± 8.6a

43.9 ± 3.0a

_

Fecundity

19.1 ± 3.0b

42.3 ± 6.9a

_

7.6 ± 3.3c

46.6 ± 15.2a

_

Means in the same row followed by the same letter are not statistically different from each other (α = 0.05; LSMeans). Fecundity data were analyzed using the square root method, original means presented

PNymP pre-nymphipositional period, NympP nymphipositional period, NpDNP number of nymphs produced per day of nymphipositional period, NPD number of nymph production days, Max, maximal number of nymphs produced in a 24-h period

aAphids did not survive long enough to reproduce at 24–29°C

Russian wheat aphids on intermediate wheatgrass had a longer pre-nymphipositional period at 13–18°C than at 18–24°C (t = 3.10; df = 21; P = 0.0054). Aphids produced more nymphs per day during the nymphipositional period at 18–24°C than at 13–18°C on intermediate wheatgrass (t = −2.38; df = 21; P = 0.0270). There were more nymph production days at 18–24°C than at 13–18°C for aphids feeding on crested wheatgrass (t = −2.60; df = 21; P = 0.0168) and intermediate wheatgrass (t = −4.27; df = 21; P = 0.0003).

The maximum number of nymphs produced in a 24-h period was lower for aphids feeding on intermediate wheatgrass at 13–18°C than at 18–24°C (t = −3.94; df = 21; P = 0.0008). Aphids feeding on intermediate wheatgrass at the 13–18°C temperature also had a lower maximum number of nymphs produced in a 24-h period than aphids on crested wheatgrass at the same temperature (t = 2.33; df = 21; P = 0.0301).

Lower fecundity was found at 13–18°C compared to 18–24°C for aphids feeding on crested wheatgrass (t = −2.15; df = 21; P = 0.0431) and intermediate wheatgrass (t = −4.31; df = 21; P = 0.0003). Fecundity was higher on crested wheatgrass than on intermediate wheatgrass at 13–18°C (t = 2.20; df = 21; P = 0.0389).

Mean generational time was calculated using a fitted least mean square approach; therefore, statistics about the central tendencies of the means were not calculated (Table 4). Mean generational times were longer at the lower temperature regime (13–18°C) for aphids on both crested (30.9 days) and intermediate wheatgrass (37.6 days) compared to the higher temperature regime (18–24°C). Generational times were slightly lower for crested (29.4 days) and intermediate wheatgrass (27.8 days) at 18–24°C.
Table 4

Mean generation time and intrinsic rate of increase for RWA2 on crested and intermediate wheatgrass at 13–18°C, 18–24°C, and 24–29°C at 14:10 (L/D) photoperiod

Test parameter

Crested wheatgrass

Intermediate wheatgrass

13–18°C

18–24°C

24–29°Ca

13–18°C

18–24°C

24–29°Ca

Mean generation time

30.9

29.4

_

37.6

27.8

_

Intrinsic rate of increaseb

0.120

0.170

_

0.055

0.199

_

Mean generation time and intrinsic rate of increase (Birch 1948) values were fitted (i.e., optimized) using fitted least mean square approach; therefore, statistical information about the central tendencies of the means were not calculated

aAphids did not survive long enough to reproduce at 24–29°C

bIntrinsic rate of increase was calculated using methods developed by Birch (1948)

Russian wheat aphids feeding at the higher temperature regime (18–24°C) on intermediate wheatgrass had the greatest intrinsic rate of increase (rm = 0.199), followed by aphids feeding on crested wheatgrass at 18–24°C (rm = 0.170), crested wheatgrass at 13–18°C (rm = 0.120), and intermediate at 13–18°C (rm = 0.055) (Table 4).

Aphids did not survive long enough to reproduce at the 24–29°C temperature regime; therefore, no data were collected. Randolph et al. (2008) and Girma et al. (1990) conducted similar studies on wheat and found longevity and reproductive rates were reduced under this same temperature regime. Merrill et al. (2009) found that Russian wheat aphid mortality increased as temperatures increased above 18.4°C. Crested and intermediate wheatgrass hosts may be too low quality to support the Russian wheat aphid under consistently harsh environmental conditions which is typical of the eastern Colorado wheat growing region during the summer months. According to the results of this study, the Russian wheat aphid would not be able to effectively reproduce on crested and intermediate wheatgrass at consistently warm temperatures.

In addition, this study suggests that temperatures consistently cooler than a range of 18–24°C would result in decreased reproduction on crested and intermediate wheatgrass. When an aphid is feeding on a low quality host, unfavorable changes in environmental conditions may decrease reproductive ability more than if the aphid was feeding on a better quality host. Overcoming the pressures presented by low quality hosts would allow aphids to better utilize noncultivated hosts in more variable environments. Russian wheat aphids are known to use noncultivated hosts in montane environments (Randolph et al. 2011), where they can experience extreme temperature variability. If these aphids were able to overcome host selective pressures by genetic mutation or recombination, reproduction could be increased resulting in a large adaptive advantage. Noncultivated hosts in agricultural and montane environments may play an important role in maintaining Russian wheat aphid genetic diversity.

These results indicate that Russian wheat aphids could use alternate hosts as population sources throughout the oversummering period. Intrinsic rates of increase, while lower than on wheat, are high enough that population increases should be expected in areas where the temperature regimes remained moderate or low. Moreover, selection pressures to overcome antixenosis or antibiosis by the Russian wheat aphid are likely high in these hosts (relative to wheat), indicating the possibility for selection of biotypes that are potentially virulent to winter wheat.

Acknowledgments

We would like to thank Jeff Rudolph for maintaining the RWA2 colony. This research was supported by the Colorado Agricultural Experiment Station Project 646, Biology and Management of Russian Wheat aphid, Diuraphis noxia (Kurdjumov), in Colorado.

Copyright information

© Springer Science+Business Media B.V. 2011