الفهرس 
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Abstract
Field studies were carried out at the University of Mansoura, Egypt and the University of California. Riverside, USA, to study the economic decision levels of three insect pests in cotton fields under the narural conditions, namely the Cotton aphid, Aphis gossypii, the silverleaf whitefly, Bemisia argentifolii, and the pink bolworm. Pectinopbora gossypiella, ( rom 1990 to 1994. The populations of these insect pests as well as the predators were monitored, in cotton fields free of insecticides and fields treated with insecticides. by the two sampling methods, visual examination and the sweep net. Sticky yellow cards were used to monitor the whitefly population. The insecticide treated fields received normal regime of recommended by the technical staff of the Plant Protection Division of Agricultural Authorities of Dakahlia Governorate. A. Survey of Cotton Insects. Six insect orders were recorded during this study. These orders were Homoptera, Coelopte ra. Hemiptera , Lepidoptera. Neuroptera and Thysanoptera. order Homoptera was the most numerous in 1990 & 1991. while order Thysanoptera was the lowest abundant.
In Egypt, the cotton aphid Aphis gossypii has become a key pest or cotton, showing about 56.13% in 1990 and 41.99 % in 1991 of the total percent of harmful insects. It was followed by the sweetpOlatO whitefly Oemisia tabaci during 1990 which occupied the 1st position in Egyptian cotlon fields during1991, Forming about 49% of the total injurious insects, The cotton leafhopper Empoasca lybica had a low population density. The onion thrips Thrips wbaci, NezaTa lIiridula, Spodoptera ialoraiis, Agrotis ipsiloll and Lygus hespems represented a very little important pest complex. in the cotton fields in the both years. In U. S. A., the silverleaf whitefly Bemisia argentifolii was the most common im sect pest of cotton and constitated about 83% in 1993 and 94% in1994 of the total insects. On the contrary. the COtton aphid A. gossypii, the cotton leafhopper E. Iybiro, Amrasca bigutellil were occasional and potential pests in 1993 & 1994.