الفهرس 
Corn borers as economic pests infesting corn plants (Zea mays)Only 14 pages are availabe for public view
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Abstract
Field experiments were carried out during two successive seasons of 2007 and 2008. In the growing season of 2007, the study was carried out in five field sites located in four Egyptian governorates: El-Shrouk-Noubaria (Behaira), Salhia (Esmailia), Bassyoun (Gharbia) (harvested for maize silage), 10-Bezour-Noubaria (Behaira) and Bdahel (Beni Swief) (harvested for maize grain). In the growing season of 2008, three planted locations were studied: 10-Bezour-Noubaria (Behaira), Bassyoun (Gharbia) and Bdahel (Beni-Swief) harvested for maize grain. In all locations, the Bt corn hybrid (MON 810 event: Ajeeb YG®) was compared with the non Bt-corn hybrid (Ajeeb®) as conventional plants. Tthe recommended agricultural practices were followed during both seasons according to the recommendations of the Egyptian Ministry of Agriculture. So, this study aimed to evaluate the Bt hybrid plants (MON 810 event:Ajeeb YG®) under the Egyptian filed conditions with the natural infestation by corn borers namely, Sesamia cretica Led., Ostrinia nubilalis (Hb.) and Chilo agamemnon (Bles.).
Therefore, experiments were established in the field at five locations in 2007 and three locations during 2008 planted with Bt and non -Bt varieties to
study the effect of the encoding Bt gene in corn plants (Ajeeb YG®) as a genetically modified hybrid) and conventional non Bt hybrid (Ajeeb®) on the incidence of three corn borers, namely, the pink corn borer, Sesamia cretica Led., the purple-lined corn borer, Chilo agamemnon Bles. and the European corn borer, Ostrinia nubilalis Hbn. under Egyption field conditions, Also, the study included the ecological effects of the Bt corn on a certain beneficial non-target organisms such as the predaceous bug Orius spp. (as a naturally biological control agent) and soil micro- organism (via soil enzymes activity as an indicator of that effect). Also, the yield of grain and silage in Bt and non-Bt maize hybrids were determined. Economics, profits with reference to yield losses in Bt corn were also calculated and predicted. The results can be summarized as follows:
5.1. Influence of the Bt-corn hybrid (MON 810 event:Ajeeb YG®) on the incidence of the three corn borers species in certain Egyptian governorates
5.1.1. During the growing season of 2007
5.1.1.1. The pink stem borer, Sesamia cretica Led.
Generally, data indicated that there were significant differences between the infestation of S. cretica in Bt and the non Bt maize hybrids during the whole season in all locations. The Bt-plants of Ajeeb YG® hybrid gave a complete avoidance of Sesamia cretica infestation (0.00 larvae or pupae/plant) throughout the three growing stages of the tested corn plants in all locations, while the infestation of the pink borer S. cretica throughout the stage of 8-leaves/plant in the non Bt hybrid was higher than the other two stages in all locations, except in El-Shrouk-Noubaria (Behaira).
During the pre-harvest stage, the mean number of larvae and/or pupae/plant in the non Bt hybrid was declined to 0.05, 0.68, 0.00, 0.00, 0.075 larvae/plant in 10-Bezour-Noubaria (Behaira), El-Shrouk-Noubaria (Behaira), Salhia (Esmailia), Bassyoun (Gharbia) and Bdahel (Beni Swief), in respect. Meanwhile, at the flowering stage, the mean number of living larvae and/or pupae/plant was 0.10, 1.05, 0.33, 0.15 and 1.15 in 10-Bezour-Noubaria (Behaira), El-Shrouk-Noubaria (Behaira), Salhia (Esmailia), Bassyoun (Gharbia) and Bdahel (Beni Swief), respectively. The relative high infestation of S. cretica at this stage of the non Bt hybrid was noticed at Beni Swif governorate (the only inspected location in the Upper Egypt).
5.1.1.2. The purple-lined corn borer, Chilo agamemnon Bles.
The living larvae or pupae/plant of C. agamemnon in the Bt hybrid throughout the whole season at the three inspected plant growing stages in all locations was 0.00. It was obvious that the infestation by this insect at the 8-leaves stage wasn’t observed in all locations cultivated by both hybrids, except Bassyoun (Gharbia) that showed 0.18 living larvae or pupae/plant in the non Bt hybrid. In relation to the pre-harvest stage, a relatively decreased infestation was observed. The corresponding mean values were 0.48, 0.25 and 0.05 larvae or pupae/plant for 10-Bezour, Bdahel and El-Shrouk, respectively. No infestation evidence of C. agamemnon was recorded in this stage for Ajeeb® hybrid in Salhia and Bassyoun. However, the infestation of C. agamemnon at the flowering stage was significantly increased in the non Bt hybrid in all locations, except Salhia (Esmailia) and Bassyoun (Gharbia), where the infestation was 0.00%. The infestation was 1.28, 0.35 and 0.20 living larvae or pupae/plant for the field sites of 10-Bezour-Noubaria (Behaira), Bdahel (Beni Swief) and El-Shrouk-Noubaria (Behaira), respectively.
5.1.1.3. The European corn borer, Ostrinia nubilalis Hbn.
The Bt-plants of Ajeeb YG® hybrid gave a complete avoidance of C. agamemnon infestation (0.00 larvae or pupae/plant) throughout the three growing stages of the tested corn plants in all locations. The infestation of O. nubilalis in the conventional hybrids was the highest compared with S. cretica and C. agamemnon. In the flowering stage, (early infestation) infestation rates were 3.7, 1.95 and 0.45 living larvae or pupae/plant in Salhia, Bassyoun and bdahel, respectively. However, the infestation rate was also detected in all locations throughout the pre-harvest stage. The mean numbers of living larvae or pupae were 4.25, 2.78, 1.13, 0.60 and 0.58/plant in Salhia, Bassyoun, El-Shrouk, Bdahel and 10-Bezour, respectively.
5.1.1.4. Summing up the infestation levels of each corn borer all over the whole season of 2007
The Bt corn plants showed a complete defense to the infestation by the three corn borers due its content of Bt toxin throughout the whole season (0.00 larvae or pupae/plant) in all locations. Vice versa, the non Bt corn plants were more susceptible to the infestation of the three corn borers for the three inspected stages. The calculated total mean number of S. cretica allover the whole season were 2.54, 2.18, 1.95, 1.69 and 0.72/plant in Bdahel, El-Shrouk, Bassyoun, Salhia and 10-Bezour, respectively. Moreover, Salhia (Esmailia) and Bassyoun (Gharbia) registered the highest infestation of 7.95 and 4.73 larvae or pupae of O. nubilalis /plant, respectively.
In respect to the infestation by C. agamemnon, 10 -Bezour-Noubaria (Behaira) showed the highest infestation (1.75 larvae or pupae/plant), while Salhia (Esmailia) was free from this insect pest.
The high infestation expressed as the mean number of the three corn borers together in the non Bt hybrid was 9.64 in Salhia, followed by 6.86, 4.24, 3.56 and 3.09 larvae or pupae/plant in Bassyoun , Bdahel , El-Shrouk-Noubaria and 10-Bezour-Noubaria ,respectively.
In general, the above mentioned data demonstrated that the non Bt corn was highly susceptible to the infestation with the three corn borers in all locations in different governorates especially Esmailia, Gharbia and Beni-Swief, while the Bt corn was totally free from the infestation with the three corn borers.
5.1.2. During the growing season of 2008.
5.1.2.1. The pink stem borer, Sesamia cretica Led.
The Bt corn plants clarified a complete resistance to the infestation of S. cretica throughout the 8-leaves stage (0.00 larvae or pupae/plant) in all locations. On the other hand, the high mean rates of S. cretica infestation were observed at the 8-leaves stage of the tested non Bt hybrid (Ajeeb®) recording 0.60, 1.60 and 1.50 larvae or pupae/plant in 10-Bezour-Noubaria, Bassyoun and Bdahel , respectively. Slight infestation rate was observed in the flowering and/or the pre-harvest stages. The mean number of larvae or pupae/plant in the non Bt corn (Ajeeb®) in Behaira, Gharbia and Beni Swief governorates were 0.20, 0.10 and 0.00, respectively. In the pre-harvest stage, the infestation was only detected in 10-Bezour-Noubaria (Behaira) giving 0.13 larvae or pupae/plant.
5.1.2.2. The purple-lined corn borer, Chilo agamemnon Bles.
There was no infestation of C. agamemnon at the 8-leaves stage observed in the Bt and non Bt hybrids among the three locations (0.0 larvae/plant). There weren’t any remarkable infestation symptoms in both Bt plants. The infestation of C. agamemnon has been started during the flowering stage and the mean numbers of larvae/plant in the non Bt corn (Ajeeb®) at Behaira, Gharbia and Beni- Swief were 0.93, 0.30 and 0.40, respectively. The mean number of C. agamemnon larvae/plant during the pre-harvest stage was 1.94 in Gharbia followed by 0.20 in Beni Swief.
5.1.2.3. The European corn borer, Ostrinia nubilalis Hbn.
The infestation rate of O. nubilalis in non Bt corn (Ajeeb®) was relatively higher in the pre-harvest stage than in the flowering one at all locations. The mean number of living larvae or pupae/plant in flowering stage was 0.13, 0.70 and 0.30 in 10-Bezour-Noubaria (Behaira), Bassyoun (Gharbia) and Bdahel (Beni Swief), respectively.