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Abstract
SUMMARY
The main objective of the research work in this dissertation is to develop new approaches for the control of the cotton leafworm within an IPM program which include rationalization of the use of synthetic insecticides, and maximizing the role of the biological control agents. The new approach was to benefit from the sunflower plants as surrounding rows to the field plots of the cotton plants. Sunflower plants were found to attract beneficial biological control agents, and to reduce the field build-up up of the cotton leafworm Spdoptera littoralis population. This initial field observation and its field application was followed by investigating the main chemical constituent in the sunflowers which is responsible for its beneficial field characteristics. The responsible chemical constituent was proved to be the polyhydroxy flavone quercetin. This finding lead to further testing of quercetin when used in joint action with various insecticides under lab. and then field conditions in combating the cotton leafworm. Finally the biochemical mode of action of quercetin was verified as a successful plant antioxidant. The results of the present study can be summarized as follows:
A. The benefit of sunflower plant as traps surrounding the field plots of cotton:
The field results proved the role of the sunflower plants in attracting beneficial insects and thus resulting in reducing the level of field infestation of the cotton plants with Spodoptera littoralis larvae. Field data during the two successive seasons 2004, 2005 revealed that:
a. The number of the following predators per plot were recorded in cotton plant field plots surrounded by either one or two rows of sunflower in comparison with the plots without: surrounding rows Cocclinella unoleeimpunctata, Paederus alfierii, Chrysopa vulgaris, Orius laevigauo, Scymnus syriacus.
The total number of predators of insects and mites in the cotton plots surrounded by either one or two rows of sunflower plants significantly exceeded that number in the cotton plots without. The recording period of time was from June 5 up till August 28 in both 2004 and 2005 seasons.
b. Simultaneously, the least number of cotton leafworm Spodoptera littoralis larvae infestation was in the cotton plots surrounded by either one or two rows of sunflower infestation during the two successive seasons of 2004 and 2005.
B. Lab. study of the antifeeding properties of quercetin to Spodoptera littoralis larvae.
When the 4th instar larvae of Spodoptera littoralis were treated with 400 ppm of quercetin, the larvae showed abnormal behaviour by stop feeding followed by retardation in growth and development leading to reduction in larval weight, and growth and thus slower pupal formation. Deformation of pupae and moths and reducing up to 50% in egg laying at the level of 400 ppm was also recorded as a result of quercetin application to the insect larvae.