A Research on population development of some cotton pests in relation to various cotton varieties and number of insecticide applications

A RESEARCH ON POPULATION DEVELOPMENT OF SOME COTTON PESTS IN RELATION TO VARIOUS COTTON VARIETIES AND NUMBER OF INSECTICIDE APPLICATIONS Kadri ye ÜLGEN (M. Se. Thesis) SUMMARY In this study, Çukurova 1518,Stonville 453, Çun 82 and Deltapine 20 cotton varieties which have different characters were tested in Antalya province. Their resistance against the important cotton pests, the population development of important cotton pest and the effects of the number of insecticide applications on pest populations and the yield were investigates. Three insect species, the tobacco whitefly (Bemisia tabaci Genn), the cotton aphid (Aphis gossypii Glov. ) and the leafhopper (Asymmetrasca decedens Paol ı ) were found to be major pest. While tobacco whitefly and cotton aphid populations were not important early in the season, leafhopper appeared tobe important pest. Tobacco whitefly and cotton aphid populations started to build up by the end of July, and peaked rapidly to high populations with the second irrigation. The population levels of other insects remained very low. Among the varieties tested Çukurova 1518 and Çun 82 were found to be resistant to the tobacco whitefly, but it is sensitive to cicadellids. Stonville 453 and Deltapine 20 varieties appeared to be sensitive to the tobacco whitefly. There was no any significant differences between control and number of insecticide applications in terms of population development of insects. Only one insecticide application did not affect the size of insect populations significantly, but two and three insecticide applications reduced the tobacco whitefly and the cotton aphid populations rapidly. There were significant differences in yield between varieties and between the number of insecticide applications. Stonville 453 and Deltapine 20 varieties gave higher yields than the rest. Despite the resistance they showed against the tobacco whitefly the yields of Çukurova 1518 and Çun 82 varieties were low. As to the effect of the number of insecticide applications on the yield, higher yields were obtained in plots with three insecticide applications than in control plots. Also, many beneficial insects which were dependent on cotton pests were found. The beneficial insects; especially predatory coccinellids and hemipterans were found densely. Among the coccinellid predators, Scymnus spp. were the most abundant. The predatory hemipteran population increased when tobacco whitefly, Thrips tabaci Lind. and leafhopper populations were high, but decreased when pests populations were low. There was no. any significant effects of varieties and the number of insecticide applications on the predator populations. DEPARTMENT : PLANT PROTECT I ON Year:1993 Page : COMMITEE: Assist. Prof. Dr. Hüseyin GÖÇMEN (Advisor) Prof. Dr. îr fan TUNÇ Prof. Dr. Oktay YEGEN