الفهرس 
aim of the work
population studies of cereal aphids infesting wheat plants and their natural enemiesOnly 14 pages are availabe for public view
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Abstract
The present investigation was undertaken at the Experimental
Farm of Assiut University, Agronomy Department, throughout 2010-
2011 and 2011-2012 wheat growing seasons.
The objectives were initiate to study: Monitor the seasonal
population of cereal aphids, Study the relationship between cereal
aphid populations and biotic and abiotic factors in Assiut, discuss
the status of some wheat varieties and advanced lines resistant to
cereal aphid species, to assess the damage caused by cereal aphids.
1-Aphid species infesting wheat plants and their natural
enemies:
1.1-Aphids:
Owing to field survey studies through 2010-2011 and 2011-
2012 wheat growing seasons, four cereal aphid species belonging to
order Homoptera Family Aphididae were found infesting wheat
plants in Assiut. These species were; the corn leaf aphid,
Rhopalosiphum maidis (Fitch); the oat bird-cherry aphid,
Rhopalosiphum padi (Linnaeus); the greenbug, Schizaphis
graminum (Rondani) and the English grain aphid, Sitobion
(Marcosiphum) avenae (Fabricius).
1.2-Natural enemies:
Predators:
The following predator species were found in association
with cereal aphids during the study period (2010-2012):
Chrysoperlla carnea Steph. (Chrysopidae: Neuroptera), Coccinella
undecimpunctata L. (Coccinellidae: Coleoptera), Nabis spp.
(Nabidae: Heteroptera), Orius spp. (Anthocoridae: Heteroptera),
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Paederus alfierii (Koch) (Staphilinidae: Coleoptera), Scymnus spp.
(Coccinellidae: Coleoptera), Syrphus corolla Fab. (Syrphidae:
Diptera) and some unidentified species of true spiders.
Parasitoids:
The following primary parasitoid species recorded emerged
from mummies of cereal aphid belonging to Fam. Aphidiidae from
wheat fields: Diaretella rapae (M’Intosh), Paraon necans
(Mackauer) and Aphidius gr. colemani (Viereck).
2-Dominance (%) and Abundance (%) of cereal aphids:
In general, data show that R. padi followed by S. graminum
seems to be the most important economic pests infesting wheat
plants at Assiut as indicated by the highest value of dominance and
abundance degrees.
3-Population studies of aphid species infesting wheat:
The population of S. graminum, R. padi and R. maidis on
wheat plants began to appear on wheat plants on 1st week of January
with few numbers when the plants were in the tillering stage (ZGS
30). Afterwards, the population of aphids increased gradually to
reach a peak of abundance during the end of February. Then the
number of aphids began to decline until the end of March, when the
aphid disappeared from the plants.
Natural enemies:
Predators and hymenopterous parasitoids peaked in the meddle
of March during the initial population decline of aphid populations.
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4- Population age structure of cereal aphids:
In general regardless of the aphid species and the wheat
growing seasons it could be concluded that:
Density 1 (d1): The initial population density of cereal aphids was
detected with an average 7±2.83 days.
Density 2 (d2): In this phase the population of aphids increased
slowly to reach 10% of the maximum level with 31±4.24 days.
Density 3 (d3): Aphid populations increased to a maximum level
within an average of 8-9 weeks.
Density 4 (d4): The fourth phase includes the population decline,
which usually starts shortly as the population peaked. The present
data show that the population declined to reach 10% of the
maximum level with an average of 78.5±4.95 days (11-12 weeks).
Density 5 (d5): disappearance of aphids from wheat fields that has
been observed within an average of 84±2.83 days, from the
beginning of January.
5- Susceptibility of wheat cultivars / advanced lines to cereal
aphids:
The data given show the different degrees of susceptibility of
the tested wheat cultivars / advanced lines to cereal aphids in Assiut.
S. graminum, R. padi and R. maidis were recorded as the dominated
aphids in wheat cultivars /advanced lines in this study.
In general, it was found that all tested wheat cultivars /
advanced lines were infested by those aphid species. However, the
population densities of R. padi are much higher followed by S.
graminum on all tested cultivars / advanced lines. R. maidis and S.
aveane were usually scarce.
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The analyses of variance (Anova) of data showed that
significant differences between the tested cultivars / advanced lines
to their susceptibility to infestation by cereal aphids.
2011 season:
Maximum aphid populations were found on Sakha 93 and
Assiut 303 (26.00 and 25.30 aphids per tiller, respectively).
The lowest aphid numbers (18.85, 18.75 and 18.60 aphids /
tiller) were recorded on Assiut 248, Assiut 216, and Sids 1,
respectively.
Wheat cultivar Assiut 706, Assiut 303, Sakha 93, and Sids
12 harboured the highest numbers of cereal aphid complex during
2011 with an average of 21.25±0.52, 25.30±0.38, 26.00±0.97 and
22.05±0.95 aphids / tiller, respectively. It appeared as the
susceptible (S) cultivars / advanced lines. However, the lowest
numbers were recorded on remain cultivars / advanced lines. These
cultivars appeared as moderately resistant (MR) to infestation by
cereal aphids (table 26).
2012 season:
The highest number of aphids per tiller (724.45±67.22
aphids / tiller) was recorded on Sakha 93, whereas the lowest
numbers (109.90±13.26 aphids / tiller) was recorded on Assiut 248.
The wheat cultivar Sakha 93 harboured the highest numbers
(724.45 aphids / tiller) during 2012. This cultivar appeared as high
susceptible (HS). However, the lowest numbers were recorded on
the cultivars Assiut 248, Assiut 216, Assiut 733, Sakha 94, Sids 1
and Giza 168 with an average of 109.90±13.26, 131.80±7.25,
144.75±8.11, 171.55±14.79, 128.00±8.40 and 167.25±3.96 aphids /
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tiller, respectively. This cultivars / advanced lines appeared as low
resistance (LR). The cultivars, Assiut 706, Assiut 303 and Sids 12
were appeared as susceptible (S) with an average of 315.45, 433.70
and 386.50 aphids / tiller, respectively.
6-Tolerance category:
Yield and other yield related parameters (No of days of 50%
heading, height of plants, number of spikes/plant, number of
spikelets / spike, length of spike/plant, weight grain (gm) of spike,
1000 grain weight (gm), grain yield / plant (gm) and grain yield /
plot (kg) were recorded at the end of the experiments in both treated
and untreated plots.
The analysis of variance of yield components of wheat
cultivars / advanced lines as affected by cereal aphid infestation
showed highly significant differences among the studied traits under
controlled (free from aphid infestation) and uncontrolled (with aphid
infestation) experiments during 2011 and 2012 seasons.
The above mentioned agronomical characteristics as well as
chemical analysis of water contents, soluble sugar and soluble
protein were correlated with aphid infestation to find relationship
between them. Overall cereal aphids had shown non significant
correlation with water content, soluble sugar, soluble protein, days
to 50% heading, spike length and weight 1000 kernels. Population
of aphids was significantly negatively correlated with plant height,
number spike / plant, kernels / spike, weight grain / spike, grain
yield / plant and grain yield / plot (r= -0.81, -0.63, -0.73, -0.55, -0.97
and -0.94, respectively).
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Grain yield / plant loss assessment:
2011 season:
Assiut 248, Assiut 216, Assiut 733 and Sids 1 produced
highest yield (21.09, 21.21, 20.98 and 21.91 gm / plant,
respectively) followed by Assiut 706, Sakha 94, Sids 12 and Giza
168 (19.09, 19.13, 18.65 and 19.43 grain yield gm / plant). Assiut
248, Assiut 216 and Sids 1 had better resistance to aphid than all
other cultivars / advanced lines. The lowest yielding cultivars /
advanced lines were Assiut 303 and Sakha 93 (15.96 and 15.51
grain yield (gm) / plant). The perusal of the data revealed that
cultivars / advanced lines having maximum attack of aphid had
lower yield and vice versa. Also there was a decline in grain yield /
plant in various cultivars / advanced lines ranging from 2.65 to
18.44% with increasing infestation of aphid.
2012 season:
Under controlled experiments (treated). Data in Table 44 and
illustrated in Figure 23 show that Assiut 248, Assiut 216, Assiut
303, Assiut 733, Sids 1 and Sids 12 produced highest grain yield /
plant (24.82, 23.56, 23.22, 23.52, 23.64, and 23.24 gm / plant,
respectively) followed by Assiut 706, Sakha 94, and Giza 168
(22.36, 21.93, and 21.98 grain yield gm / plant). Assiut 248 and Sids
1 had better resistance to aphid than all other cultivars / advanced
lines. In the second experiments (Untreated plants), the lowest
yielding cultivars / advanced lines were Assiut 303 and Sakha 93
followed by Sids 12 (15.87, 8.07 and 17 grain yield (gm) / plant).
The perusal of the data revealed that cultivars / advanced lines
having maximum attack of aphid had lower yield and vice versa.
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Also there was a decline in grain yield / plant in various cultivars /
advanced lines ranging from 7.74 to 35.39% with increasing
infestation of aphid.
Grain yield / plot loss assessment:
2011 season:
In the control plants (treated), average grain yield / plot (kg)
(table 45) ranged from 0.82 kg / plot for the cultivar Sakha 93 to
1.30 kg / plot for Sids 1. In the untreated, the maximum grain yield /
plot 1.23 kg / plot in cultivar Sids 1 followed by 1.16 and 1.13 kg /
plot for Assiut 216 and Assiut 733, respectively. The minimum
grain yield (kg) / plot were 0.61 kg / plot for Sakha 93. Minimum
decrease in grain yield / plot was recorded in Assiut 248, Assiut
216, Assiut 733 and Sids 1, 6.73%, 5.69, 7.38, and 5.38,
respectively. Maximum reduction in the grain yield was recorded in
cultivar Sakha 93.
2012 season:
Under controlled experiments (treated), average grain yield
(kg) / plot ranged from 0.61 kg / plot for the cultivar Sakha 93 to
1.25 kg / plot for Assiut 248. In the untreated, the maximum grain
yield / plot were recorded in line Assiut 248 (1.08 kg / plot) and the
minimum 0.39 was found in variety Sakha 93. However, the
reduction (%) in the grain yield / plot showed a highly significantly
difference due to aphid attack indicating 36.06% for Sakha 93
followed by Assiut 303 (32.94%). Minimum reduction in the grain
yield / plot was recorded in Assiut 248 with 13.60%, followed by
Sids 1 with 14.72% and Assiut 216 with 15.24%.