ANBAR JOURNAL OF AGRICULTURAL SCIENCES

Abstract

Afield experiment was conducted at the field of the College of Agriculture, Abu-Ghraib, Baghdad to evaluate the efficacy of two sampling methods, the direct method and the sweeping – net , to estimate the population density of some insects and mites associated with the foliage of three cotton varieties (Abu-Ghraib , Daes and Ashur). A sampling program on a regular basis has been developed during the season. Results showed clear differences in the types and numbers of insects collected in every method way. The main species collected by the two methods were: the whitefly, Bemesia tabaci, leaf hopper, Asymmetrasca decedents and cotton thrips, Thrips tabaci. There were no significant differences in the numbers of the whitefly for the three varieties by the direct method which amounted to (3.89, 4.39, 4.09) individual/ 5 leaves respectively, while there were significant differences when using the sweep– net, in which the highest numbers was recorded on Daes (6.05/ 5 leaves), which/ differed significantly from the numbers on the varieties Ashur and Abu-Ghraib (11.7 and 13.00)/ 5 leaves respectively. There were no significant differences in the numbers of leaf hopper, A. decedents and cotton thrips T. tabaci colleted in every way for the three varieties. The leaf hopper numbers ranged between 15.39 to 16.19/ 5 leaves by the direct method and 1.80 to 1.39/ 10 sweep-net, while thrips numbers ranged between 1.29 to 1.39/ 5 leaves and, 1.19 to 1.42/ 10 sweep– net. In addition to the main insects species collected above, other species collected by the sweep– net alone included: the cotton seed bug, Oxycarenus hyalipennis, bud and flower bug, Crenotides pallidus (Rambur). Among insect predators collected both methods on all varieties the ladybird, Coccinella septumpuntata L., the ladybird with 11– spots, C. undecimpuntata L., numbers of the last species have been higher on Abu– Ghraib variety (1.32/ 5 leaves), compared 0.89 and 0.99/ 5 leaves for the varieties Daes and Ashur respectively. The anthocorid bug, Orius albidipennis (Reuter) numbers were higher on the variety Ashur (1.06/ 5 leaves), compared with (0.79, 0.89)/ 5 leaves on the varieties Abu-Ghraib and Daes, respectively. Numbers of syrphid fly was relatively similar on all varieties and ranged between (2.18– 2.39)/ 5 leaves. The, aphid lion, Chrysoperla sp. and Scymnus sp. Were collected in low numbers from the varieties by the sweeping– net. The possibility of benefit from the use of the two sampling methods for detecting the presence of insect pests and their predators and to assess vital numerical density in cotton fields also discussed.