الفهرس 
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Abstract
The present studies were conducted on cereal aphids infesting wheat plants in Assiut and aimed to:
1- Survey aphid species infesting wheat plants and study their population 2- Figure out the relationship between some factors (biotic and abiotic) and
cereal aphid populations
3- Survey of mycopathogens infecting cereal aphids under field conditions
and studying their relation to aphid population
4- Isolation of some entomopathogenic fungi from collected cereal aphid
cadavers and testing their vierulence and pathogenicity.
The following are summarizes the results:
Cereal aphid species
Three species of cereal aphids were found infesting wheat plants at Assiut, Egypt during 2013 and 2014 growing seasons, namely; the oat bird-cherry aphid, Rhopalosiphum padi L.; the corn leaf aphid, Rhopalosiphum maidis (Fitch) and the greenbug, Schizaphis graminum (Rondani). The most common cereal aphid species, R. padi and S. graminum, in wheat at Assiut.
Cereal aphid population
The aphid started to appear on wheat plants in extremely low numbers during the first week of January when the plants were in the tillering stage. Its population reached a peak around the middle of February when the plants were in the booting stage. The population continued in relatively high numbers in the next weeks and declined from the field during the end of March when the plants were in the ripening stage.
Relationship between population of cereal aphid and some abiotic and biotic factors
The population of cereal aphids appeared with a few numbers during the first week of January. In this time the plants were in the tillering stage coincided with a plant age of 51 days, temperature ranged from 7.43 to 21.57°C and relative humidity ranged from 14.86 to 72.71%. The initial infestation with aphids was correlated with few numbers of cadavers. The data revealed also that the population of aphids increased markedly by the progress of wheat plant growth toward maturity and the maximum population densities of aphids occurred when the plants were in the booting stage. In this point plant age was in an average of 93 days. This period (mid-February) coincided with a maximum temperature ranged from 25.71 to 26.71°C and maximum RH ranged from 72.43 to 73.57%. These conditions seem to be the favorable range for the reproduction and multiplication of the cereal aphids on wheat plants. However, the rapid increase in the population of aphid in this period might be related to suitability of the host plant. The number of cadavers progressively increased to exhibit a peak nearly after the aphid population reached a peak. The data showed a decline in the aphid population during the end of March. This period coincided with the end of ripening growth stage of wheat plants. The prevailing maximum temperature ranged from 27.71 to 29.00°C and maximum RH ranged from 65.43 to 74.00%. This decline of aphid population results from rapid DROP in the suitability of the crop, accompanied by much alate emigration and the action of the natural enemies of aphids.
Mycopathogens as natural enemies of cereal aphids
Mycopathogens identified attacking cereal aphids
Nine species including six entomophthorales and three hyphomycetes were surveyed and identified infecting the above cereal aphid species. Entomophthorales was represented by six species belonging to three families. Ancylistaceae was represented by one species, Conidiobolus coronatus. Entomophthoraceae was represented by four species, Entomophthora planchoniana, Pandora (=Erynia) neoaphidis, Zoophthora radicans and Zoophthora occidentalis. Neozygitaceae was represented by one species Neozygites fresenii. The identified species of Hyphomycetes fungi belonging to order Moniliales were represented by three species (Family: Moniliaceae) namely: Beauveria bassiana, Verticillium lecanii and Paecilomyces lilacinus.
Incidence of recorded mycopathogens
During 2013 there were 503 individuals were recorded infected from 3508 alive individuals from the cereal aphid species representing 14.34% mortality rate due to mycoses. Nine species were identified and their abundance could be arranged decsendingly as follows: C. coronatus was the dominant species with a rate of occurrence reaching 26.64%, followed by E. planchoniana (23.46%). Pandora neoaphidis, P. lilacinus, V. lecanii, N. fresenii, Z. radicans and B. bassiana inflecting 11.13, 9.54, 9.34, 6.76, 6.56 and 6.16 % of the total fungi recorded respectively. Z. occidentalis showed the least occurrence (0.41 %).
During 2014, 1331 individuals were recorded infected from 4674 alive individuals from the cereal aphid species representing 28.48% mortality rate during the whole season due to mycoses. Eight species were identified and their abundance could be arranged descending as follows: C. coronatus and E. planchoniana were the predominant species with 35.83 and 29.53 % of the total fungi recorded. P. neoaphidis, V. lecanii, N. fresenii, P. lilacinus and B. bassiana had 8.79, 8.26, 6.19, 4.28 and 3.98 % of the total fungi. Z. radicans had the least percentage (3.23).
Effect of some abiotic factors on incidence of entomopathogenic fungi
Multiple regression analysis was used to declare the relationship between four selected abiotic factors: temperature (maximum (x1) and minimum (x2), relative humidity (maximum (x3) and minimum (x4) in relation to incidence of entomopathogenic fungi.
During 2013 season, simple correlation analysis revealed a highly significant positive effect of the maximum R.H. (x3) minimum R.H. (x4), maximum temperature (x1) and minimum temperature (x2) (r= 0.93, 0.91, 0.87 and 0.86, respectively). However, coefficient of determination (R2) was 0.85 indicating that the mentioned tested variables were responsible together for 80% of the changes of aphid population.
Concerning, 2014 growing season, the simple correlation coefficients of the studied variables were significant. The multi-regression analysis revealed that the studied variables were responsible for 0.77% of the changes in the incidence of entomopathogenic fungi. Most of the changes in the aphid population (88.73%) out of total of 67.39, 58.64, 56.27 and 52.88 were related to the maximum temperature, minimum relative humidity, maximum relative humidity and minimum temperature respectively.
Physiological studies on isolated entomopathogenic fungi
1-Enzymatic activity of B. bassiana and P. lilacinus isolates
The enzymatic activity of two isolates of B. bassiana and one isolate of P. lilacinus isolated from cereal aphid cadavers directly collected from wheat plants Assiut have been studied.
Lipase
All tested isolates were able to produce lipolytic enzymes, but isolate of P. lilacinus was the most active.
Protease
Proteolytic activity (caseinolysis) was positive in all cultures and the best activity was detected in culture of P. lilacinus.
Chitinase
The tested isolates gave positive activity (growth and clear zone). However the best isolates of chitinase activity was P. lilacinus.
2- Pathogenicity of B. bassiana and P. lilacinus against the corn leaf aphid R. maidis
P. lilacinus
Apterous forms of R. maidis were inoculated with different concentrations of P. lilacinus conidia (2x107, 2x106, 2x105 and 2x104). All the experimented concentrations resulted in mortality percentages of 100, 80, 65 and 45% respectively.
B. bassiana 1
Concentrations of 1.8x107, 1.8x106, 1.8x105 and 1.8x104 conidia / ml were able to kill 85, 65, 60 and 55% respectively.
B. bassiana 2
All concentration of B. bassiana (2) spore suspensions are able to kill the corn leaf aphid in various mortality percentages ranging from 65 to 95%
Generally, the rise of the conidial concentration induced regular increase in mortality percentage. By contrast, mortality in the control treatment recorded 2.50%.
3- Virulence of P. lilacinus and B. bassiana against R. maidis
The LC50 were calculated as 1.35x105, 4.45x103 and 5.52x102 (slope= 0.63±0.03, 0.28±1.92x102x and 0.37±2.38x102x) for isolates of P. lilacinus, B. bassiana (1) and B. bassiana (2) respectively.
B. bassiana (2) isolate was more aggressive than other isolates as indicated by low value of LC50 compared with other isolates.