الفهرس 
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Abstract
The present study was carried out at the experimental farm of
Faculty of Agriculture, Moshtohor, Zagazig University using com
variety (Treble cross 310) which considered one of the major cereal
crops. Field experiments were carried out during two successive
maize seasons 1996 and 1997 to determine the effect of three
planting dates (April, May and June), three nitrogen fertilizer levels
(70, 100 and 130 N units/fed.) and two insecticides (Lannate 900/0
and Malathion 57%) on rate of infestation by the three corn borers
(Sesamia cretica Led., Chilo agamemnon Bles. and Ostrinia
nubilalis Hbn.), rate of infestation by the com leaf aphid
Rhopalosiphum maidis, number of aphid and its aphidivorous
insects, yield of com grains and number of hibernating com borers
larvae inside the plants before and after harvesting.
I. Effect of planting dates:
1. Data revealed that infestation of maize plants with corn borers
was higher in 1996 than 1997 in the three sowing dates. The
three planting dates may be arranged in descending order
according to their rates of infestation for the two seasons as
follows, April plantation received highest rates of infestation
(74.2 and 50.6%) followed by the third (11.4 and 12%) and
finally the May plantation which received the lowest infestation
with corn borers (4.8 and 3.1%) for the two seasons,
respectively. So to avoid the heavy infestation with com borers,
maize plant must be sown during May. The analysis of varience
showed highly significant differences between first and both and third plantations in 1997 season, while in 1996
season there was high significant differences between the three
plantations regarding corn borers infestation.
2. The rate of infestation with corn leaf aphid and number of its
main predators were studied under the effect of the three sowing
dates. The seven predators were Chrysoperla carnea, Paederus
aifierii, Scymnus spp, Coccinella septempunctata, C.
undecimpunctata, Cydonia vicina var. nilotica and Cydonia
vicina var isis.
Generally, the infestation with aphids was higher in 1996 than
1997 maize season. The plants of first plantation (sown in April)
were not infested with aphids until harvesting time while the plants
of the second sowing date (sown in May) received the highest
number of aphids than the third plantation in 1996. There were high
rates of infestation on the first half of August which reached 1000/0.
There was high significant differences between the three
sowing dates under study in the two seasons regarding the number
of aphids and subsequently the rate of infestation with aphids.
The highest number of predators recorded ten plants
throughout the two seasons 1996 and 1997, respectively were 15 &
18 individuals for the first sowing date, 115 and 9 individuals for
the second sowing date while the highest abundance were 27 and 15
individuals on the third sowing date. But generally, it may be
concluded that the overall means of predators were higher in 1996
(8.8, ~2.8 and 13.7 predators/plant) than 1997 (9.3,4.0 and 5.1) on
first, second and third plantation, respectively. This is may due to
the infestation of maize plant with com borers and com leaf aphid
was higher in 1996 than 1997.
As for the effect of planting dates on yield of com ears,
results obtained in the present experiment showed that the
difference in yield of ears per feddan between them was significant
in both seasons. In 1997 season, May and June plantation gave the
best yield (19.5 and n03 ardab/feddan, respectively), while the
lowest yield was obtained from April planting (14.0 ardab/feddan)
which harbourd more com borers than the other two plantations.
So, the differences in yield/feddan between early and late
plantations may be attributed to the levels of infestation by com
borers and also to the complex of the prevailing environmental
factors.
II. Effect of nitrogen fertilizer levels:
Ammonium nitrate was used at three levels (130, 100, 70 N
units of fertilizer/feddan). Results indicated that there was
significant relation between the degree of maize cultivars infestation
by com borers and nitrogen fertilizer application at 70 units level,
while insignificant at the two other levels and control in 1996
season, while in 1997 the three levels of nitrogen fertilization
showed insiginficant effects on maize plant infestation with com
borers.
As for infestation with com leaf aphids and their predators
data showed that infestation rates with aphids were markedly
affected by adding nitrogen fertilizers in 1996, where the overall
means were 92, 85, 87.5 and 60% for the levels 130, 100, 70 and
zero units of nitrogen/fed., respectively. There were significant
variation between the number of aphids and aphid infestation rates
at the three levels of nitrogen and control.
In 1997 the present study showed that rates of infestation with
aphids were higher on fertilized plants than control where the
overall means of percentage of infestation were 8.6, 8.3, 7.1 and
3.40/0 on maize plants applied with 130, 100, 70 and zero units
N.Ifed., respectively.
The relation between aphid infestation rates of maize plants
and levels of nitrogen fertilization were significant between zero
fertilization and other nitrogen levels while was insignificant
between the three position addition of nitrogen.
Number of aphids were higher on fertilized than unfertilized
plants, where the numbers were 8.2, 4.6, 3.6 and 0.5
individuals/plant as seasonal overall means at the levels 130, 100,
70 and zero units of nitrogen/fed., respectively in 1997.
Data showed that total numbers of predators were higher on
fertilized maize plants with three levels of nitrogen. The numbers of
predators were 805, 1074 and 548 individuals for 1996 and 351,
301 and 340 predators for 1997 at the levels 130, 100 and 70 units
of nitrogen/fed., respectively. These numbers were higher
comparing with those in the case of control showing 240 and 157
individuals in the two successive seasons, respectively.
The predators, can be arranged in a descending order
according to their abundance on maize plants to 3 groups. Highest
abundance (ladybird), relatively high abundance (Rove beetle) and
lowest abundance (Aphid lion).
The present study showed that the addition of any of the
different nitrogenous fertilization levels caused increase in
infestation rate of com borers, corn leaf aphid and ears yield/fed.
compared with untreated maize plants which showed reduction in
infestation rates with com borers and aphids and also reduction in
ears yield. The means of ears yield/fed. were 23.5, 19.8, 17.5 and
8.3 ardab/fed. for the two seasons with the following nitrogen levels
130, 100, 70 and zero units of nitrogen/fed. , respectively.
III. The effect of certain insecticides on rate of damage:
Hl.a, Effect of Lannate on corn borers:
Generally, infestation rate of maize plants by com borers did
not abviously increase after application of Lannate 90%. Lannate
used at two concentrations 300 g/400 L water/fed. (recommended
concentration) and 200 g/400 L water/fed. (lower than recommended).
The infestation rates by borers on control were higher than treated
plants, during the two seasons, where the overall means of
infestation were 1.20/0in 1996 and 3.8% in 1997 with recommended
concentratien, while on untreated plants were 7.0 and 5.7 during
1996 and, respectively.
Lower concentration of Lannate was less effective on the rate
of infestation by com borers showing 3.0 and 4.40/0during 1996 and
1997, respectively as overall mean of infestation.
III.b. Effect of Malathion on the infestation percentage and
abundance of R. maidis and its predators:
Generally, infestation to maize plants by com leaf aphid was
higher in 1996 than 1997. In the two seasons, rate of infestation by
aphid, number of aphids and their predators were higher on
untreated maize plants than plants treated with two concentrations
of Malathion. The used concentrations were 1.5 & 1 L/600 L
water/fed. The overall means of infestation rate by aphid were 95.5
and 14%) on untreated plants during 1996 and 1997, respectively.
While, those were 88 & 94 and 8.7 & 13.30/0on maize plants treated
with recommended and low concentrations of Malathion during
1996 and 1997, respectively. The overall mean of aphid number
with recommended and low concentrations of Malathion and
untreated plants were 391.7,512.2 and 1439.4 individuals/one plant
during 1996. Also, the overall mean number of aphidivorious
insects on treated plants with recommended and low concentration
of Malathion and on untreated maize plants were 13.2, 13.5 and
24.6 predators/l 0 plants throughout 1996, while during 1997, were
3.6, 4.4 and 4.6 individuals/lO plants, respectively. Higher effect on
number of aphids and their predators was obtained using
recommended concentration of Malathion than lower concentration.
I.V. Effect of different treatments on hibernating larvae after
harvesting:
Because of the hibernating larvae are the main source of
infestation to the plants of the next season, this point was carried
out to determine the effect of different treatments on number of
hibernating larvae inside dry stalks of treated com. The plants were
examined at the mid of winter (lOth of January).
Data showed that the dry stalks of the late sowing possessed
higher infestation with com borers and number of hibernating
larvae and pores than the stalks of early sowing. Also, infestation
with com borers and number of hibernating larvae increased by
increasing the level of nitrogen fertilization up to 100 units of
nitrogen/fed. and after which they decreased by increasing the level
of nitrogen fertilization. Also, the present work indicated that the
treatments with Malathion at 1.5 and 1 L/fed. and with Lannate at
300 and 200 glfed. gave a good protection to the treated green
plants from infestation with com borers but this protection decrease
by lapse of time.