الفهرس 
MATERIALS AND METHODSOnly 14 pages are availabe for public view
 |  | from | 119 |  |  |
| | | from | 119 | | |
Abstract
The present study was carried out in the Agricultural College Fann in Assiut during the three
successive growing seasons 1996, 1997 and 1998. Fifteen cultivars of sorghum were planted on 25
June in complete randomized
blocks with four replicates for each cultivar. The obtained results summarized as follows
I - Mon itoring abundance of the sorghum key insect pests and thei r associated natu ral
predators.
The population fluctuat ion of the sorghum key insect pests and their associated predators
differed from year to year and regardless of the seasons it found the following:
The populat ion of the pests appeared on 22nd J uly for Rhopa/osiphum maidis, 26th August for ,
’c/11zaphis graminum, 1 5th Ju ly for J,emothirps cerealium, Sesamia cretica and . jmdoptera exigua
and then t heir populations increased to reach peaks of I 059, 1 17, 26 .26 in divid ual s,
2.34 and 0.67 infested pl ants/30 plants on 26th August, 1 6th September, 22nd J uly, 19t h August
and 22nd J uly for the previous pests respecti vely. The populations then declined .
The populations of the associated predators appeared from J uly 1 5!.b. to September 30th with
peaks of abunda nce on September 2nd (for Coccinella spp. with an average of 6.06 ind ividual s/30
plan ts), J uly 29!.b. (for Scymnus spp., Orius spp. and the true spider with averages of 5.58,
1.14 and 3.32 individuals/30 plants, respectively) and on September 9th (for Peadrus sp. with an
average of 1 .05 individuals/30 pl ants).
2. Susceptibility of sorghum cultivars to certain sorghum insect pests:
Data indicated that the high susceptible cultivars were SC 338 (IS 6984C) and ATX 623 (S23)
to Sesamia cretica; SC 905 (IS 7399C), SC
229 (IS 530C) and SC 964 (IS 2765C) to Spodoptera exii>ua; SC 905 (IS 7399C) and SC 229 (IS 530C)
to R. maidis; SC 338 (JS 6984C), SC 905 (IS 7399C) and BTX 630 to Schizaphis graminum and SC 338
(IS 6984C), SC 964 (IS 2765C) and SC 804 (IS 6968C) to Limothrips cerealiwn.
The moderate resistance cultivars were SC 195 (IS l 1 16C) and SC 964 (IS 2765C) to Sesamia
cretica; ATX 623, SC 146 (IS I 2637C), SC 423
(IS 2579C), BTX 630 and SC 804 (JS 6968C) to Spodoptera exigua;
SC 964 (JS 2765C) and RQL 36 to R. maidis: SC 964 (J S 2765C) and
SC 229 (IS 350C) to S. graminum and SC 48 (J S I 2564C) to L.
crealium .
The cult ivars that have not been mentioned were between these extremes.
3- Biologica l studies on Rhopalosiphum maidis:
The durat ion period of the nymphal stage was 1 1 .76, 7.2 and 5.72 days and the pre-vi viparity
period was 1 . 1 8, 0.85 and 0.86 days at constant temperat ures of 15, 20 and 25°C, respecti vely.
Temperature threshold for the development of the nymphal stage was 7 .10°C and the thennal
units necessary for the nymphal development was
102.13 day-degrees (DD).
Life table parameters was as following:
a - The reproduction rate (Ro) were 1 .56, 3.92 and 3.42 at the constant temperatures of 15,
20 and 25°C, respecti vely.
b - Mean generation time (GT) was 16.03, 9.76 and 7. 17 days at 1 5, 20 and 25°C, respecti
vely.
c - Population doubling time (DT) of the aphid was 24. 75, 4.98 and 4.05 at 15, 20 and 25°C,
respectivel y.
d - Intrinsic rate of increase (nn) was 0.028, 0. 139 and 0.1 7 1 and the
finite rates of increase (A.) was 1 .028, 1 . 149 and 1 . 186 at 1 5, 20 and 25°C, respecti vely.
e - Number of generat ions of R. maidis which could develop 111 one season on sorghum
under Assi ut cond itions was about II.
4- Effect of some Bacillus thuringiensis form u lations, Neem extract and .J uven i le horm on e
m im ic on sorgh u m in festa tion by la rge suga r-ca n e worm, Sesamia cretica Led. a n d t h ei
r associated pred ators:
The effect of the Bacillus thuri11gie11si.1· fonnulation s (SA N 4 I5 I, Thuricide HP, Delfen,
Protecto), the Neem extract (Nemazal ) and the .luveni l honnone mimic (Admeral ) on sorghum
infestat ion by large sugar-cane worm, Sesamia cretica Led., and the associated predators were
evalua ted. Data revealed that the B.t-fomrnlat ion SAN 4 I5 I, Nemazal and Admera l were the most
toxic compounds against the pest, since they exhibited infestat ion reduction of 67 .60, 62.30
and 61 .68%, respecti vely. On the other hand. the
least effective compounds was Thuricide HP with infestation red uction of 37.07%.
Data also indicated t hat the plants in conh·ol plots harbored significantly more number of the
pest and their associated predators than the treated plots.
The tested Bt-fonnulations were less hannful to the associated predators whereas the Neem
extract (Nemazal) and the Juvenil honnone mimic (Admeral) were the most hannful tested compounds.
5 - Determ ine the resista nce level of the green bug field strain to the recommended aph
idcids:
Toxicity of mal athion, pi rimiphos-met hyl , profenofos, carbosulfan and pirimicarb were
laboratory evaluated against the fiel d and laboratory strains of the greenbug, Schizaphis
graminum (Rondan i ). Profenofos and malath ion were the most potent compounds against the fiel d
population, whereas pirimicarb was l ess toxic one. The field strain showed hi ghly resistant l
evel to pi rimicarb ( 1 83.23-fold) and moderately resista n t to carbosulfan (23.94- fold) and
profenofos (26-fold ) as compared with the laboratory strain .