ABSTRACT
The chemical resistance to the cotton boll worms; P. gossypiella and E. insulana was investigated in nineteen cottons, which included three Egyptian varieties of Gbarbadense and 16 varieties and traits of the upland cotton, G hirsutum. The nineteen cultivar lines were grown in the field in a random plot experiment and their infestation by the two boll worms was determined over two agricultural seasons. Flower buds, squars and boils, of resistant and susceptible cultivar lines were extracted for their contents of prominent secondary plant products; condensed tannins, flavonoids, and terpenoid aldehydes. The antibiotic activity of the extracts against several growth and developmental parameters of the two insects was determined in a laboratory feeding tests mixed with artificial diet. Information from laboratory and field infestation experiments correlated these allelochemicals to actual field resistance. The results show that different lines, each with insect resistance, possess different ratios of antibiotic compounds, which provide means for generation of lines with multiple factors -for resistance