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Influence of water and nitrogen fertilizer on biology of the Russian wheat aphid (Homoptera: Aphididae) on wheat
Crop Prorecaon Vol. 14. No. 2. pp. 16WY. 1YYS Copyright @ Iv95 Elsevier Science Ltd Prmted in Great Britain. All rights reserved 0261.2194/Y5 $10.00 + IMI
Influence of water and nitrogen fertilizer on biology of the Russian wheat aphid (Homoptera: Aphididae) on wheat T. I. Archer’,
E. D. Bynum Jr, A. 6. Onken and C. W. Wendt
Texas Agricultural
The effect (Mordvilko), 0.05)
Experiment
of water
and nitrogen
on field-grown
among fertilizer
March
to 4 April
Station, RT 3, Box 219, Lubbock,
(N)
fertilizer
rates (O-134 kg N ha-‘).
1988 on wheat
growing
season. More
different
@ < 0.05) between
on densities
wheat was determined. There
were significantly
that was not irrigated
irrigation
treatments
of Russian wheat
aphid,
Diuruphis
Aphid densities were not significantly
than 60 cm of rain fell during
plots that were not irrigated
TX 79401, USA
noxia (p <
(p < 0.05) more aphids from 22
than on wheat irrigated April
different
and aphid numbers
four times during the were not significantly
until 17 May 1988. By then, plants were stressed in the
and aphid densities were again higher than on plants in the plots that had
been irrigated four times. Significantly (p < 0.05) more Russian wheat aphids were found on wheat plants grown in lysimeters maintained at 15% soil water holding capacity (SWHC) in a rainout shelter than on plants in lysimeters maintained at 50 and 100% SWHC.
Keywords:
Russian wheat aphid; water; fertilizer; wheat
The Russian wheat aphid (RWA), Diuraphis noxia (Mordvilko), is reported to exploit stressed wheat, Triticum aestivum L. (Walters, 1982). Therefore, manipulating agronomic practices such as irrigation and the amount of fertilizer used to grow the crop may be useful for the management of RWA. In laboratory experiments, there has been a mixed response by RWA to fertilizer. Moon et al. (1989) recorded more RWA on wheat grown with high concentrations of nitrogen (N) (52.5 and 210 ppm N) than on the lowest concentration (10.5 ppm), but means were not separated statistically. Riedell (1990) found a negative relationship between RWA damage to wheat and the amount of N applied to wheat. Results from laboratory research indicate that the rate of increase by several aphid species declines as drought stress increases in wheat plants (Sumner et al., 1983a, b; Dorschner et al., 1986; Fereres et al., 1988). Kennedy, Lamb and Booth (1958) hypothesized that aphids on many crops do better when the host is experiencing intermittent water stress. They speculated that the high solute : water ratio in stressed plants produces a better host for aphids. Some scientists (Dorschner et al., 1986; Baugh and Phillips, 1991) think that aphid damage on wheat is greater when plants are water stressed. Previous research indicates that response to fertilizer and water is not consistent among aphid species. Therefore, data should be collected for each species. Also, because much of the aphid research has been conducted in the laboratory, data are required from the field where management systems will actually be used. The present research was designed to determine the ‘To whom correspondence
should be addressed
effect of water and fertilizer on RWA densities using field-grown wheat. Materials
and methods
Field research
Research was conducted in a wheat field arranged in a split plot design (four replications) with main plots that were either irrigated or not irrigated. Sub-plots (15 m iong X 4 m wide, 26 drill rows) were fertilized with different amounts of N fertilizer. Nitrogen was applied as urea (46% N) with the amount of N per plot determined based on the result of soil analyses. All plots were fertilized with 45 kg P,Os ha-‘. Fertilizer was applied and incorporated into the soil prior to planting. In 1987-88, the N treatments were: 0, 17, 34, 50 and 67 kg N ha-‘. This range encompasses amounts of N fertilizer applied to wheat grown with limited irrigation. In 1988-89, a wider range of fertilizer rates (0,34,67,101 and 134 kg N ha-‘) were used because of the lack of RWA response to the rates used the previous year. All plots were furrow irrigated with 4.2 ha-cm of water one day after planting to provide adequate water for germination. The field was planted with 75 kg ha-’ of TAM 105 wheat seed the first week in October. After planting, 4.7, 4.2,4.3 and 4.0 ha-cm of water was added to the irrigated plot on 18 November, 24 February, 6 April and 4 May 1987-88 by furrow irrigation. On 28 January 1988 the field was sprayed with 2,4-D herbicide at 0.84 kg ha-‘. On 23 February 1988 GleanTM (DuPont Agricultural Products, Wilmington, Delaware, USA) herbicide was applied at 0.02 kg ha-‘. No herbicide was applied the second season.
Crop Protection 1995 Volume 14 Number 2
165
Water and fertilizer effects on Russian wheat aphid: T.L Archer et al. Laboratory-grown RWA were released into plots on 13 November 1987 to supplement a low natural infestation. Heavily infested wheat tillers were collected from culture flats in the laboratory and laid along one of the middle rows of each wheat plot. A week later plants in the plots were inspected to confirm aphid infestation. In 1988-89, the natural infestation in the autumn was sufficient. Wheat plants were sampled every other week beginning on 8 February 1988 and 9 March 1989. Sampling was continued into May when wheat had matured and dried down. Each sample consisted of 20 individual tillers per plot (Archer and Bynum, 1992). The number of aphids by species and beneficial insects per tiller were recorded. The percentage of tillers infested and/or damaged was determined as described by Archer and Bynum (1992). Sampled tillers were dried and dry weights determined. Rainout shelter In 1989-90, RWA response to wheat grown with different amounts of water was determined in a rainout shelter where the confounding effect of precipitation could be eliminated. A rainout shelter has been used successfully to study response of two-spotted spider mites, Tetranychus urticae Koch, to water stressed soybeans (Klubertanz, Pedigo and Carlson, 1990). Wheat was grown in 38-litre galvanized lysimeters. Lysimeters were arranged in a completely randomized block design with four replications. Before adding soil to each lysimeter, 11 kg N ha-’ fertilizer was added to the dry soil and mixed well. Each lysimeter filled with dry soil weighed 50 kg. On 3 November, seeds were planted and 10.5 1 of water was added to bring lysimeters to full soil water holding capacity (SWHC). Six TAM 105 plants were grown in each lysimeter. Lysimeters were weighed every other week through January and then weekly until harvest. Water was added on a weight basis to maintain each lysimeter at
Table 1. Russian wheat aphid densities fertilizer, with or without irrigation
the predetermined water level of 100, 50 or 15% SWHC. A total of 55.6, 30.9 and 7.2 I of water were added to the 100, 50 and 15% SWHC treatments, respectively, during the season. Lysimeters in the 15% SWHC treatment were maintained at 50% SWHC through December to avoid excess damage from cold which can occur to severely water stressed plants. These lysimeters were then allowed to dry out and were below 20% SWHC by March. Plants were infested with field-collected RWA on 8 March at growth stage 29 (Tottman and Broad, 1987). Aphids were shaken from tillers with a hand-held sieve, mixed with a wheat farina medium, and applied to the plants with the aid of an insect applicator (Davis and Oswalt, 1979). Five RWA were applied per plant in 1 ml of media. The plants in one lysimeter per treatment were not infested to provide plant data without aphids present. Beginning on 20 March, at about one-week intervals, two tillers were removed from each plant in one infested lysimeter per treatment. The number of aphids and beneficial insects were recorded per tiller. RWA densities were separated as nymphs and adults by size. After counting aphids, the tillers were dried and weighed from both infested and uninfested lysimeters. One additional tiller per plant, including the uninfested lysimeter, was used for leaf water potential measurements. A hydraulic press was used to measure the leaf water potential for the uppermost leaf that was completely emerged from the whorl. Leaf water potential measurements were made at mid-day under a clear sky. The number of tillers per plant was recorded. A lysimeter was sampled only once because tillers had to be removed to examine them for aphids. A PROC ANOVA (SAS Institute, 1987) was used to analyse the data [aphid and beneficial insect densities, aphid days (Ruppel, 1983), aphids per unit of plant dry weight, and plant damage status]. Data for the first season were analysed as a split plot design. In the
from February to May, 1988 and 1989 on wheat grown with different amounts
of nitrogen
Mean number of Russian wheat aphids f s.e.m. N (kg ha-‘)
23 Feb.
9 Mar.
22 Mar.
Irrigated (1988) 0 17 34 50 67
0.4 0.2 0.2 0.5
_+ 0.2 f 0.1 f 0.1 + 0.4
1.1 1.3 1.1 0.5 1.1
f + + f f
Not irrigated (1988) 0 17 34 50 67
0.4 0.4 0.4 0.2 0.1
+ + + * +
2.0 1.5 1.5 0.9 1.0
+ 1.1 i- 0.4 + 0.5 +- 0.4 * 0.4 * * + ? +
0.1 f 0.1
Irrigated (1989) 0 34 67 101 134 Means
in each column
0.1 0.2 0.2 0.1 0.03
-
0.05 0.09 0.01 0.36 0.29
per irrigation
166 Crop Protection
treatment
1995 Volume
0.5 0.6 0.8 0.2 0.6
0.9 1.2 1.7 1.1 2.0
0.03 0.04 0.01 0.19 0.11
for each year
were
14 Number 2
f + f + +
20 Apr.
3 May
17 May
2.8 2.4 4.1 2.2 4.6
+ f * f +
1.0 0.8 1.1 0.8 1.3
11.3 8.6 7.7 14.5 12.8
+ + + + f
2.4 2.3 2.1 3.5 3.4
19.4 18.7 19.1 28.1 31.8
+ f f f +
3.6 3.3 3.1 4.2 4.8
24.9 15.2 14.0 28.6 34.3
f + + f +
3.5 + 0.9 4.8 f 1.1 6.0 + 1.6 3.7 + 1.1 4.2 + 1.3
5.9 3.5 5.4 3.8 7.1
+ i f + +
1.4 0.8 1.5 0.9 1.6
6.7 13.7 10.3 10.6 12.8
+ + t -t f
1.9 2.8 2.5 2.2 3.0
13.2 16.8 25.5 19.8 22.8
+ i t + f
3.0 3.7 4.3 3.7 3.9
28.1 25.4 45.7 37.9 44.1
f 5.2 + 5.1 f 6.1 f 6.1 _+6.0
0.1 0.1 0.5 0.4 0.5
0.4 1.2 1.4 2.5 2.0
+ * f + +
0.2 0.5 0.3 0.6 0.7
4.2 6.9 7.7 7.6 11.9
+ f + + +
1.4 1.9 2.3 1.8 2.7
11.7 22.3 20.8 14.3 29.1
f + f f f
2.5 4.5 4.1 3.1 4.6
+ * f + +
0.3 0.6 0.6 0.4 0.8
4 Apr.
0.06 0.03 0.27 0.22 0.22
not signifjcantly
different
@ i
0.05;
SAS
Institute,
1987)
-
3.4 2.5 2.5 4.7 5.0
Water and fertilizer effects on Russian wheat aphid: T.L Archer et al. second year, fertilizer data were analysed as a randomized complete block design because data were collected only in the irrigated plot. In the rainout shelter experiment, PROC GLM (SAS Institute, 1987) analysis was made of aphids (nymphs, adults and total), beneficial insects, tiller dry weight, number of tillers per plant and leaf water potential. Means were separated using the t-test between main plots in 198788 or the least significant (I.s.) means method in other experiments (SAS Institute, 1987). Results and discussion Field research The effect of N fertilizer on RWA increase was studied during two seasons (1987-88 and 1988-89). In the first year, fertilizer treatments were evaluated in the irrigated and not irrigated main plots. In the second season, severe cold during the autumn and winter significantly reduced the number of plants in the not irrigated main plot, so data were only from fertilizer treatments in the
irrigated main plot. There were no significant differences (p < 0.05) in RWA densities among fertilizer treatments (Table I) and the irrigation X fertilizer interaction was not significant @ < 0.05). RWA data were converted to aphid days and weighted by plant dry weight, but still there were no differences (p < 0.05) among fertilizer treatments. There was no statistical difference Cp < 0.05) in percentage of tillers infested or damaged by RWA among fertilizer treatments. Few greenbugs, predators or parasites were recovered in samples so these data are not reported. RWA densities were significantly (p < 0.05) higher on 22 March and 4 April 1988 in the main plot that was not irrigated (Figure I). More than 60 cm of rain fell during April and aphid numbers were not significantly different (p < 0.05) between main plots until 17 May 1988 when the field had dried and plants were stressed in the treatments that were not irrigated. Again, the most aphids were found in plots that were not irrigated.
-1.5 -1.0
-0.s
0.0
m
Irrigated
m
Not irrigated
23 Feb.
9
22 Mar.
4
20 Apr.
3
,
,
I
I
,
17 29
2a
May
Figure 1. Mean (+s.e.m.) number of Russian wheat aphids on wheat plants either irrigated or grown without supplemental irrigation in 1987-88. Means on each date designated with @ < 0.01) or * @ < 0.05) were significantly different using the t-test (SAS Institute, 1987). Amount of precipitation and irrigation water applied during the aphid sampling period are shown at the top of the figure. l
l
I
Mar.
4
24l AC.
21
3 May
Figure 2. Mean (+-s.e.m.) tiller dry weight, number of tillers per plant, and leaf water potential for wheat plants grown in lysimeters maintained at 100, 50 and 15% of soil water holding capacity (SWHC) in 1989-90. Means on each date in each graph designated by the same letter were not significantly different using I.s. means @ < 0.05; SAS Institute, 1987)
Crop
Protection
1995 Volume
14 Number
2
167
Water and fertilizer effects on Russian wheat aphid: T.L Archer et a/. Rainout
shelter
Wheat plants tended to compensate for the reduced water in the 50% SWHC treatment by producing significantly (p < 0.05) fewer tillers than in the fully watered lysimeters (Figure 2). As a result, plants in the 50% SWHC lysimeters were able to maintain the same leaf water potential (except on 20 April 1990) and tiller dry weights (until 3 May 1990) as in the fully watered treatment. Leaf water potential reached -2.3 MPa in the dry treatment on 27 April 1990. Aphid infestation did not affect leaf water potentials for plants in any treatment. RWA was the only aphid species found on plants in the lysimeters. One month after infesting the wheat with RWA, there were significantly (‘JJ< 0.05) more aphids on plants in the driest treatment than in the two treatments receiving the most water (Figure 3). This response was similar for aphids in the nymph and adult categories. Aphid densities continued to increase in the dry treatment, but densities in the two wet treatments hardly changed throughout the experiment. This is in contrast to data reported for other aphid species on wheat where aphid (Rhopalosiphum maidis, Schizaphis
graminum, and Sitobion avenue) densities were reduced by water stress (Sumner et al., 1983a, b; Fereres et al., 1988). Apparently, RWA are much more tolerant of
severe drought stress and can obtain nutrients even when leaf water potential was significantly (p < 0.05) reduced (Figure 3). There was less than one beneficial insect per tiller and their densities did not differ statistically (p < 0.05) among treatments. The results indicate that water stress is more important for RWA increase than is the amount of N fertilizer available to a crop. Therefore, supplemental irrigation during periods of low precipitation may be a useful management option to reduce RWA rate of increase.
Acknowledgements
The authors appreciate reviews by Keith Pike and Charles Summers. This paper has been approved for publication as TA 30698 by Director, Texas Agricultural Experiment Station, College Station.
References 90
1
I
I
I
I
I
a SO-
Total RWA per tiller
70 60 -
m
loO%SWHC
m
5O%sWHc
50 -
B
Baugh, B. A. and Phillips, S. A. Jr (1991) Influence density and plant water potential on Russian (Homoptera: Aphididae) alate production. Environ.
a
15%SWHC
a
NS
b
for disAdmin.,
Dorschner, K. W., Johnson, R. C., Kikenbary, R. D. and Ryan, J. D. (1986) Insect-plant interactions: Grcenbugs (Homoptcra: Aphididae) disrupt acclimation of winter wheat to drought stress. Environ. Entomol. 15, 118-121
10 0 70 Nymphs per tiller 60 a
a
Fereres, A., Gutierrez, C., Del Estal, P. and Castanera, P. (1988) Impact of the English grain aphid, Sitobion avenue (F.) (Homoptera: Aphididae), on the yield of wheat plants subjected to water deficits.
T
Environ. Entomol. 17, 59MO2
Q
40
Kennedy, J. S., Lamb, K. P. and Booth, C. 0. (19.58) Responses of in host plants in pots. Entomol.
Aphis fubae Stop. to water shortage Exp. Appl. 1, 274-291
Klubertanz, T. H., Pedigo, L. P. and Carlson, R. E. (1990) Effects of plant moisture stress and rainfall on population dynamics of the twospotted spider mite (Atari: Tetranychidae). Environ. Entomol. 19, 1773-1779
30 20 10
Moon, C. E., Lewis, B. E. Thompson, D. C. and Sanderson, S. A. (1989) The effects of nitrogen on the fecundity of Russian wheat aphid. Proc. Russian Wheat Aphid Conf. pp. 160-164
0
2o1
Adults per tiller
a
a
10
Riedell, W. E. (1990) Tolerance of wheat to Russian wheat aphids: nitrogen fertilization reduces yield loss. J. Plant Nutrition. 13, 579-
584
0
20
29
4
Mar.
20
26
3
Apr.
May
Figure 3. Mean (+s.e.m.) number of Russian wheat aphids (nymphs, adults and total aphids) per tiller on plants grown at 100, 50 and 15% soil water holding capacity (SWHC) in 1989-90. Means on each date in each graph designated by the same letter were not significantly different using I.s. means @ < 0.05; ISA.9 Institute, 1987)
Crop
Entomol. 20,
Davis, F. M. and Oswalt, T. G. (1979) Hand inoculator pensing lepidopterous larvae. US Dept Agric., Sci. & Educ. Advances in Agric. Technol. AAT-S-9
30 -
168
of population wheat aphid
1344-1348
40 -
20 -
Archer, T. L. and Bynum, E. D., Jr (1992) Economic injury level for the Russian wheat aphid (Homoptera: Aphididae) on dryland winter wheat. 1. Econ. Entomol. 85, 987-992
Protection
1995 Volume
14 Number
2
Ruppel, R. F. (1983) Cumulative insect-days protection. J. Econ. Entomol. 76, 375-377
as an index
SAS Institute (1987) SAS User’s Guide: Statistics, Analysis Systems institute, Cary, NC, USA, 1290 pp
of crop Statistical
Sumner, L. C., Eikenbary, R. D. and Johnson, R. C. ( 1983a) Survival and reproduction of Rhopalosiphum maidis (Fitch) (Homoptera: Aphididae) on winter wheat during simulated drought stress. J. Kans. Entomol. Sot. 59, 561-563 Sumner,
L. C., Need, J. T., McNew,
R. W., Dorschner,
K. W. and
Water and fertilizer effects on Russian wheat aphid: T.L Archer et al. Eikenbary, R. D. (1983b) Response of Schizaphis graminum (Homoptera: Aphididae) to drought-stressed wheat, using polyethylene glycol as a matricum. Environ. Entomol. 12, 919-922
Walters, M. C. (1982) Progress in Russian Wheur Aphid (Diuruphis noxia Mordvilko) Research in the Republic of South Africa, Vol. 191. Perskor, Pretoria. 78 pp
Tottman, D. R. and Broad, H. (1987) The decimal code for the growth stages of cereals, with illustrations. Ann. Appl. Biol. 110,
Received 9 April 1993 Revised 16 May 1994 Accepted 17 May 1994
441-44s
Crop Protection 1995 Volume 14 Number 2
169
Influence of water and nitrogen fertilizer on biology of the Russian wheat aphid (Homoptera: Aphididae) on wheat T. I. Archer’,
E. D. Bynum Jr, A. 6. Onken and C. W. Wendt
Texas Agricultural
The effect (Mordvilko), 0.05)
Experiment
of water
and nitrogen
on field-grown
among fertilizer
March
to 4 April
Station, RT 3, Box 219, Lubbock,
(N)
fertilizer
rates (O-134 kg N ha-‘).
1988 on wheat
growing
season. More
different
@ < 0.05) between
on densities
wheat was determined. There
were significantly
that was not irrigated
irrigation
treatments
of Russian wheat
aphid,
Diuruphis
Aphid densities were not significantly
than 60 cm of rain fell during
plots that were not irrigated
TX 79401, USA
noxia (p <
(p < 0.05) more aphids from 22
than on wheat irrigated April
different
and aphid numbers
four times during the were not significantly
until 17 May 1988. By then, plants were stressed in the
and aphid densities were again higher than on plants in the plots that had
been irrigated four times. Significantly (p < 0.05) more Russian wheat aphids were found on wheat plants grown in lysimeters maintained at 15% soil water holding capacity (SWHC) in a rainout shelter than on plants in lysimeters maintained at 50 and 100% SWHC.
Keywords:
Russian wheat aphid; water; fertilizer; wheat
The Russian wheat aphid (RWA), Diuraphis noxia (Mordvilko), is reported to exploit stressed wheat, Triticum aestivum L. (Walters, 1982). Therefore, manipulating agronomic practices such as irrigation and the amount of fertilizer used to grow the crop may be useful for the management of RWA. In laboratory experiments, there has been a mixed response by RWA to fertilizer. Moon et al. (1989) recorded more RWA on wheat grown with high concentrations of nitrogen (N) (52.5 and 210 ppm N) than on the lowest concentration (10.5 ppm), but means were not separated statistically. Riedell (1990) found a negative relationship between RWA damage to wheat and the amount of N applied to wheat. Results from laboratory research indicate that the rate of increase by several aphid species declines as drought stress increases in wheat plants (Sumner et al., 1983a, b; Dorschner et al., 1986; Fereres et al., 1988). Kennedy, Lamb and Booth (1958) hypothesized that aphids on many crops do better when the host is experiencing intermittent water stress. They speculated that the high solute : water ratio in stressed plants produces a better host for aphids. Some scientists (Dorschner et al., 1986; Baugh and Phillips, 1991) think that aphid damage on wheat is greater when plants are water stressed. Previous research indicates that response to fertilizer and water is not consistent among aphid species. Therefore, data should be collected for each species. Also, because much of the aphid research has been conducted in the laboratory, data are required from the field where management systems will actually be used. The present research was designed to determine the ‘To whom correspondence
should be addressed
effect of water and fertilizer on RWA densities using field-grown wheat. Materials
and methods
Field research
Research was conducted in a wheat field arranged in a split plot design (four replications) with main plots that were either irrigated or not irrigated. Sub-plots (15 m iong X 4 m wide, 26 drill rows) were fertilized with different amounts of N fertilizer. Nitrogen was applied as urea (46% N) with the amount of N per plot determined based on the result of soil analyses. All plots were fertilized with 45 kg P,Os ha-‘. Fertilizer was applied and incorporated into the soil prior to planting. In 1987-88, the N treatments were: 0, 17, 34, 50 and 67 kg N ha-‘. This range encompasses amounts of N fertilizer applied to wheat grown with limited irrigation. In 1988-89, a wider range of fertilizer rates (0,34,67,101 and 134 kg N ha-‘) were used because of the lack of RWA response to the rates used the previous year. All plots were furrow irrigated with 4.2 ha-cm of water one day after planting to provide adequate water for germination. The field was planted with 75 kg ha-’ of TAM 105 wheat seed the first week in October. After planting, 4.7, 4.2,4.3 and 4.0 ha-cm of water was added to the irrigated plot on 18 November, 24 February, 6 April and 4 May 1987-88 by furrow irrigation. On 28 January 1988 the field was sprayed with 2,4-D herbicide at 0.84 kg ha-‘. On 23 February 1988 GleanTM (DuPont Agricultural Products, Wilmington, Delaware, USA) herbicide was applied at 0.02 kg ha-‘. No herbicide was applied the second season.
Crop Protection 1995 Volume 14 Number 2
165
Water and fertilizer effects on Russian wheat aphid: T.L Archer et al. Laboratory-grown RWA were released into plots on 13 November 1987 to supplement a low natural infestation. Heavily infested wheat tillers were collected from culture flats in the laboratory and laid along one of the middle rows of each wheat plot. A week later plants in the plots were inspected to confirm aphid infestation. In 1988-89, the natural infestation in the autumn was sufficient. Wheat plants were sampled every other week beginning on 8 February 1988 and 9 March 1989. Sampling was continued into May when wheat had matured and dried down. Each sample consisted of 20 individual tillers per plot (Archer and Bynum, 1992). The number of aphids by species and beneficial insects per tiller were recorded. The percentage of tillers infested and/or damaged was determined as described by Archer and Bynum (1992). Sampled tillers were dried and dry weights determined. Rainout shelter In 1989-90, RWA response to wheat grown with different amounts of water was determined in a rainout shelter where the confounding effect of precipitation could be eliminated. A rainout shelter has been used successfully to study response of two-spotted spider mites, Tetranychus urticae Koch, to water stressed soybeans (Klubertanz, Pedigo and Carlson, 1990). Wheat was grown in 38-litre galvanized lysimeters. Lysimeters were arranged in a completely randomized block design with four replications. Before adding soil to each lysimeter, 11 kg N ha-’ fertilizer was added to the dry soil and mixed well. Each lysimeter filled with dry soil weighed 50 kg. On 3 November, seeds were planted and 10.5 1 of water was added to bring lysimeters to full soil water holding capacity (SWHC). Six TAM 105 plants were grown in each lysimeter. Lysimeters were weighed every other week through January and then weekly until harvest. Water was added on a weight basis to maintain each lysimeter at
Table 1. Russian wheat aphid densities fertilizer, with or without irrigation
the predetermined water level of 100, 50 or 15% SWHC. A total of 55.6, 30.9 and 7.2 I of water were added to the 100, 50 and 15% SWHC treatments, respectively, during the season. Lysimeters in the 15% SWHC treatment were maintained at 50% SWHC through December to avoid excess damage from cold which can occur to severely water stressed plants. These lysimeters were then allowed to dry out and were below 20% SWHC by March. Plants were infested with field-collected RWA on 8 March at growth stage 29 (Tottman and Broad, 1987). Aphids were shaken from tillers with a hand-held sieve, mixed with a wheat farina medium, and applied to the plants with the aid of an insect applicator (Davis and Oswalt, 1979). Five RWA were applied per plant in 1 ml of media. The plants in one lysimeter per treatment were not infested to provide plant data without aphids present. Beginning on 20 March, at about one-week intervals, two tillers were removed from each plant in one infested lysimeter per treatment. The number of aphids and beneficial insects were recorded per tiller. RWA densities were separated as nymphs and adults by size. After counting aphids, the tillers were dried and weighed from both infested and uninfested lysimeters. One additional tiller per plant, including the uninfested lysimeter, was used for leaf water potential measurements. A hydraulic press was used to measure the leaf water potential for the uppermost leaf that was completely emerged from the whorl. Leaf water potential measurements were made at mid-day under a clear sky. The number of tillers per plant was recorded. A lysimeter was sampled only once because tillers had to be removed to examine them for aphids. A PROC ANOVA (SAS Institute, 1987) was used to analyse the data [aphid and beneficial insect densities, aphid days (Ruppel, 1983), aphids per unit of plant dry weight, and plant damage status]. Data for the first season were analysed as a split plot design. In the
from February to May, 1988 and 1989 on wheat grown with different amounts
of nitrogen
Mean number of Russian wheat aphids f s.e.m. N (kg ha-‘)
23 Feb.
9 Mar.
22 Mar.
Irrigated (1988) 0 17 34 50 67
0.4 0.2 0.2 0.5
_+ 0.2 f 0.1 f 0.1 + 0.4
1.1 1.3 1.1 0.5 1.1
f + + f f
Not irrigated (1988) 0 17 34 50 67
0.4 0.4 0.4 0.2 0.1
+ + + * +
2.0 1.5 1.5 0.9 1.0
+ 1.1 i- 0.4 + 0.5 +- 0.4 * 0.4 * * + ? +
0.1 f 0.1
Irrigated (1989) 0 34 67 101 134 Means
in each column
0.1 0.2 0.2 0.1 0.03
-
0.05 0.09 0.01 0.36 0.29
per irrigation
166 Crop Protection
treatment
1995 Volume
0.5 0.6 0.8 0.2 0.6
0.9 1.2 1.7 1.1 2.0
0.03 0.04 0.01 0.19 0.11
for each year
were
14 Number 2
f + f + +
20 Apr.
3 May
17 May
2.8 2.4 4.1 2.2 4.6
+ f * f +
1.0 0.8 1.1 0.8 1.3
11.3 8.6 7.7 14.5 12.8
+ + + + f
2.4 2.3 2.1 3.5 3.4
19.4 18.7 19.1 28.1 31.8
+ f f f +
3.6 3.3 3.1 4.2 4.8
24.9 15.2 14.0 28.6 34.3
f + + f +
3.5 + 0.9 4.8 f 1.1 6.0 + 1.6 3.7 + 1.1 4.2 + 1.3
5.9 3.5 5.4 3.8 7.1
+ i f + +
1.4 0.8 1.5 0.9 1.6
6.7 13.7 10.3 10.6 12.8
+ + t -t f
1.9 2.8 2.5 2.2 3.0
13.2 16.8 25.5 19.8 22.8
+ i t + f
3.0 3.7 4.3 3.7 3.9
28.1 25.4 45.7 37.9 44.1
f 5.2 + 5.1 f 6.1 f 6.1 _+6.0
0.1 0.1 0.5 0.4 0.5
0.4 1.2 1.4 2.5 2.0
+ * f + +
0.2 0.5 0.3 0.6 0.7
4.2 6.9 7.7 7.6 11.9
+ f + + +
1.4 1.9 2.3 1.8 2.7
11.7 22.3 20.8 14.3 29.1
f + f f f
2.5 4.5 4.1 3.1 4.6
+ * f + +
0.3 0.6 0.6 0.4 0.8
4 Apr.
0.06 0.03 0.27 0.22 0.22
not signifjcantly
different
@ i
0.05;
SAS
Institute,
1987)
-
3.4 2.5 2.5 4.7 5.0
Water and fertilizer effects on Russian wheat aphid: T.L Archer et al. second year, fertilizer data were analysed as a randomized complete block design because data were collected only in the irrigated plot. In the rainout shelter experiment, PROC GLM (SAS Institute, 1987) analysis was made of aphids (nymphs, adults and total), beneficial insects, tiller dry weight, number of tillers per plant and leaf water potential. Means were separated using the t-test between main plots in 198788 or the least significant (I.s.) means method in other experiments (SAS Institute, 1987). Results and discussion Field research The effect of N fertilizer on RWA increase was studied during two seasons (1987-88 and 1988-89). In the first year, fertilizer treatments were evaluated in the irrigated and not irrigated main plots. In the second season, severe cold during the autumn and winter significantly reduced the number of plants in the not irrigated main plot, so data were only from fertilizer treatments in the
irrigated main plot. There were no significant differences (p < 0.05) in RWA densities among fertilizer treatments (Table I) and the irrigation X fertilizer interaction was not significant @ < 0.05). RWA data were converted to aphid days and weighted by plant dry weight, but still there were no differences (p < 0.05) among fertilizer treatments. There was no statistical difference Cp < 0.05) in percentage of tillers infested or damaged by RWA among fertilizer treatments. Few greenbugs, predators or parasites were recovered in samples so these data are not reported. RWA densities were significantly (p < 0.05) higher on 22 March and 4 April 1988 in the main plot that was not irrigated (Figure I). More than 60 cm of rain fell during April and aphid numbers were not significantly different (p < 0.05) between main plots until 17 May 1988 when the field had dried and plants were stressed in the treatments that were not irrigated. Again, the most aphids were found in plots that were not irrigated.
-1.5 -1.0
-0.s
0.0
m
Irrigated
m
Not irrigated
23 Feb.
9
22 Mar.
4
20 Apr.
3
,
,
I
I
,
17 29
2a
May
Figure 1. Mean (+s.e.m.) number of Russian wheat aphids on wheat plants either irrigated or grown without supplemental irrigation in 1987-88. Means on each date designated with @ < 0.01) or * @ < 0.05) were significantly different using the t-test (SAS Institute, 1987). Amount of precipitation and irrigation water applied during the aphid sampling period are shown at the top of the figure. l
l
I
Mar.
4
24l AC.
21
3 May
Figure 2. Mean (+-s.e.m.) tiller dry weight, number of tillers per plant, and leaf water potential for wheat plants grown in lysimeters maintained at 100, 50 and 15% of soil water holding capacity (SWHC) in 1989-90. Means on each date in each graph designated by the same letter were not significantly different using I.s. means @ < 0.05; SAS Institute, 1987)
Crop
Protection
1995 Volume
14 Number
2
167
Water and fertilizer effects on Russian wheat aphid: T.L Archer et a/. Rainout
shelter
Wheat plants tended to compensate for the reduced water in the 50% SWHC treatment by producing significantly (p < 0.05) fewer tillers than in the fully watered lysimeters (Figure 2). As a result, plants in the 50% SWHC lysimeters were able to maintain the same leaf water potential (except on 20 April 1990) and tiller dry weights (until 3 May 1990) as in the fully watered treatment. Leaf water potential reached -2.3 MPa in the dry treatment on 27 April 1990. Aphid infestation did not affect leaf water potentials for plants in any treatment. RWA was the only aphid species found on plants in the lysimeters. One month after infesting the wheat with RWA, there were significantly (‘JJ< 0.05) more aphids on plants in the driest treatment than in the two treatments receiving the most water (Figure 3). This response was similar for aphids in the nymph and adult categories. Aphid densities continued to increase in the dry treatment, but densities in the two wet treatments hardly changed throughout the experiment. This is in contrast to data reported for other aphid species on wheat where aphid (Rhopalosiphum maidis, Schizaphis
graminum, and Sitobion avenue) densities were reduced by water stress (Sumner et al., 1983a, b; Fereres et al., 1988). Apparently, RWA are much more tolerant of
severe drought stress and can obtain nutrients even when leaf water potential was significantly (p < 0.05) reduced (Figure 3). There was less than one beneficial insect per tiller and their densities did not differ statistically (p < 0.05) among treatments. The results indicate that water stress is more important for RWA increase than is the amount of N fertilizer available to a crop. Therefore, supplemental irrigation during periods of low precipitation may be a useful management option to reduce RWA rate of increase.
Acknowledgements
The authors appreciate reviews by Keith Pike and Charles Summers. This paper has been approved for publication as TA 30698 by Director, Texas Agricultural Experiment Station, College Station.
References 90
1
I
I
I
I
I
a SO-
Total RWA per tiller
70 60 -
m
loO%SWHC
m
5O%sWHc
50 -
B
Baugh, B. A. and Phillips, S. A. Jr (1991) Influence density and plant water potential on Russian (Homoptera: Aphididae) alate production. Environ.
a
15%SWHC
a
NS
b
for disAdmin.,
Dorschner, K. W., Johnson, R. C., Kikenbary, R. D. and Ryan, J. D. (1986) Insect-plant interactions: Grcenbugs (Homoptcra: Aphididae) disrupt acclimation of winter wheat to drought stress. Environ. Entomol. 15, 118-121
10 0 70 Nymphs per tiller 60 a
a
Fereres, A., Gutierrez, C., Del Estal, P. and Castanera, P. (1988) Impact of the English grain aphid, Sitobion avenue (F.) (Homoptera: Aphididae), on the yield of wheat plants subjected to water deficits.
T
Environ. Entomol. 17, 59MO2
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Kennedy, J. S., Lamb, K. P. and Booth, C. 0. (19.58) Responses of in host plants in pots. Entomol.
Aphis fubae Stop. to water shortage Exp. Appl. 1, 274-291
Klubertanz, T. H., Pedigo, L. P. and Carlson, R. E. (1990) Effects of plant moisture stress and rainfall on population dynamics of the twospotted spider mite (Atari: Tetranychidae). Environ. Entomol. 19, 1773-1779
30 20 10
Moon, C. E., Lewis, B. E. Thompson, D. C. and Sanderson, S. A. (1989) The effects of nitrogen on the fecundity of Russian wheat aphid. Proc. Russian Wheat Aphid Conf. pp. 160-164
0
2o1
Adults per tiller
a
a
10
Riedell, W. E. (1990) Tolerance of wheat to Russian wheat aphids: nitrogen fertilization reduces yield loss. J. Plant Nutrition. 13, 579-
584
0
20
29
4
Mar.
20
26
3
Apr.
May
Figure 3. Mean (+s.e.m.) number of Russian wheat aphids (nymphs, adults and total aphids) per tiller on plants grown at 100, 50 and 15% soil water holding capacity (SWHC) in 1989-90. Means on each date in each graph designated by the same letter were not significantly different using I.s. means @ < 0.05; ISA.9 Institute, 1987)
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Entomol. 20,
Davis, F. M. and Oswalt, T. G. (1979) Hand inoculator pensing lepidopterous larvae. US Dept Agric., Sci. & Educ. Advances in Agric. Technol. AAT-S-9
30 -
168
of population wheat aphid
1344-1348
40 -
20 -
Archer, T. L. and Bynum, E. D., Jr (1992) Economic injury level for the Russian wheat aphid (Homoptera: Aphididae) on dryland winter wheat. 1. Econ. Entomol. 85, 987-992
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2
Ruppel, R. F. (1983) Cumulative insect-days protection. J. Econ. Entomol. 76, 375-377
as an index
SAS Institute (1987) SAS User’s Guide: Statistics, Analysis Systems institute, Cary, NC, USA, 1290 pp
of crop Statistical
Sumner, L. C., Eikenbary, R. D. and Johnson, R. C. ( 1983a) Survival and reproduction of Rhopalosiphum maidis (Fitch) (Homoptera: Aphididae) on winter wheat during simulated drought stress. J. Kans. Entomol. Sot. 59, 561-563 Sumner,
L. C., Need, J. T., McNew,
R. W., Dorschner,
K. W. and
Water and fertilizer effects on Russian wheat aphid: T.L Archer et al. Eikenbary, R. D. (1983b) Response of Schizaphis graminum (Homoptera: Aphididae) to drought-stressed wheat, using polyethylene glycol as a matricum. Environ. Entomol. 12, 919-922
Walters, M. C. (1982) Progress in Russian Wheur Aphid (Diuruphis noxia Mordvilko) Research in the Republic of South Africa, Vol. 191. Perskor, Pretoria. 78 pp
Tottman, D. R. and Broad, H. (1987) The decimal code for the growth stages of cereals, with illustrations. Ann. Appl. Biol. 110,
Received 9 April 1993 Revised 16 May 1994 Accepted 17 May 1994
441-44s
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