Joint action of quercetin with four insecticides on the cotton leaf-worm larvae, Spodoptera littoralis Boisd. (Lep. : Noctuidae) in Egypt.

The naturally occurring phytoncidal chemical component of some plant- species are responsible for controlling and/or repelling insects from host plants. The use of natural products, readily available in the environment, to control the cotton leafworm, could be of help in reducing the need for applying the synthetic conventional insecticides . Moreover, crude vegetable oils application is quite safer to the non targets and the environment. The use of sex attractant pheromones as predicative tools to forecast pest population and their potential damage levels in specific crops, has significantly been limited because sex attractants are usually directed to one sex only. Thus, identification of plant constituents that attract S. littoralis Boisd. adults, especially females, and that directly affect their feeding or reproductive behaviour, would greatly expand opportunities for manipulation of the biological and environmental events that prevent the establishment, development, and dispersal of the insect-pest under study. Extracted Volatiles from certain parts of cotton plants, attracted both sexes of the cotton leafworm moths instead of attracting one sex only as the pheromones do. Plant flavonoids have been shown by many investigators to have an effect on insect behaviour, growth, and development. Quercetin is one of many bioflavonoids that exists in several fruits and vegetables. The Aim of the present work is to study in vivo the biochemical mode of action of quercetin as a synergist in combination with insecticides. The present results proved the synergistic effect of quercetin when combined with four insecticides, namely, profenofos (organophosphates), deltamethrin (pyrethroid), and tebufenozide et hexaflumuron as insect growth regulators against the studied insect-pest. Quercetin role as a synergist might be attributed to its ability to inhibit certain active oxidases, which may be responsible for in vivo detoxification of the intact insecticides when applied to insect larvae, through glutathione-S-transferase.

Biological performance of quercetin on the cotton leaf-worm larvae, Spodoptera littoralis Boisd. (Lep., Noctuidae) and prevailing natural enemies in the Egyptian cotton fields.

The Egyptian cotton (Gossypium barbadense L.) accounts for 65 % of the world production of long stable cultivars. Taking into consideration the competition of other cotton producing countries, it should be of great importance to control pests, which attack the cotton plants to improve the yield and its quality. The main objective of this study is to develop new approaches for the management of the cotton leafworm Spodoptera littoralis Boisd. within an IPM program, that include synthetic insecticides rationalization, and maximiziation the role of the biological control agents. Sunflower plants Helianthus annuus (Asterales: Asteraceae) raised in rows surrounding plots of cotton were used as trap plants to attract some biological agents, which subsequently lead to check the build-up of the cotton leafworm population. This scientific phenomenon was attributed to the main chemical constituent of sunflower plants, which has been proved to be the polyhydroxy flavone "quercetin". Field data of the two successive seasons 2004 and 2005 revealed that: (a) the total number of insect predators, Coccinella undecimpunctata, Paederus alfierli, Chrysopa vulgaris, Orius laevigatus, Scymnus synacus, and true spiders in the cotton plots surrounded by either one or two rows of sunflower plants significantly exceeded the corresponding numbers in the cotton plots without sunflower plants., (b) the least number of cotton leafworm Spodoptera littorolis larvae infestation was recorded simultaneously in the cotton plots surrounded by sunflower plants. Moreover, laboratory studies assured the antifeeding properties of quercetin against the 4th instar larvae of Spodoptera littoralis. Quercetin at a concentration rate of 4000 ppm, showed abnormal behaviour represented in feeding stop, growth inhibition and development retardation. Deformation of pupae, moths, and reduction up to 50% in egg laying was also noticed after quercetin application to the larvae.