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Species Diversity of Insect Pests and Weeds, Disease Incidences of Cotton Agroecosystem and Development of Tools for Cotton Pest Management
Dissertation Abstract:
Field experiments were conducted at Suwan Farm, Northeastern Thailand during dry and wet seasons of 2000 and 2001, to determine the species diversity of insect pests, natural enemies, weeds, and disease incidences of cotton. The randomized complete block design with four replicates was employed on four cotton varieties/ lines, namely: AP1, AP2, SR60 (Si Samrong 60) and SD1 (Sarid 1). Shannon-Weiner diversity index was used for data analysis. It was found that 13-14 insect pests and 12-13 natural enemies appeared in cotton field regularly. The cotton leafhopper, Amrasca biguttula was observed to be the dominant species, while the least abundant species was the spiny bollworm, Earias sp., in both seasons. Various species of spiders were the most abundant natural enemies in the dry season; whereas the antlike flower beetle, Anthicus ruficollis, was the most abundant in the wet season. Fusarium boll rot and leaf spot diseases were observed in dry season while damping-off and white rot were observed in the wet season. For weeds, approximately 14 species occured in large numbers. Spatial distribution pattern and optimum sample size for cotton key pests, A. biguttula, and the cotton bollworm, Helicoverpa armigera, were analyzed using the variance-to-mean ratio, Morisita’s index, and the negative binomial parameter (k). While the distribution of A. biguttula nymphs was found as clumped, H. armiega larvae exhibited mainly clumped but sometimes randomly dispersed. The optimum sample size of 10 and 30 plants, and 15 and 30 plants per 140 m2 were obtained at low and high aggregation levels of A. biguttula nymphs and H. armiega larvae, respectively. Economic threshold levels for key pests were performed on the variety, SR60 during the wet season of 2001-2002. One nymph/leaf per 20 plants was found to be the desired economic threshold for controlling A. biguttula, while it was 5, 3, and 5 H. armigera larvae/30 plants for 30-60, 60-90, and 90-120 days age of cotton, respectively.