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The effect of twos potted spider mites, Tetranychus urticae Koch, on the yield and fiber quality of cotton was studied at high-yield levels in Australia over four field seasons. Significant reductions in yield, fiber quality, and seed viability were observed and were found to be related to the time of infestation and rate of development of twos potted spider mite populations. Early infestations (at early flowering), which increased quickly, caused the greatest reductions whereas later infestations (at first boll opening), which increased more slowly, had little effect on yield. Early twospotted spider mite infestations reduced the number of bolls set and boll size, but later infestations affected boll size only. It is proposed that by reducing the photosynthetic capacity of leaves, severe infestations of twos potted spider mite may heighten competition for assimilates among sinks within the plant (e.g., fruit and leaves), potentially causing fruit shed and limiting the development of bolls. Regression analysis indicated that yield reductions can be predicted from the rate of increase of twospotted spider mite infestations, the date at which they begin to increase, and the length of the growing season. Using this information it is possible to identify populations that are increasing at rates capable of reducing yield, allowing control to be implemented if necessary. The rate of increase of twospotted spider mites was lower on the okra leaf cultivar Siokra, than on the normal leaf cultivar, Deltapine 90, indicating that Siokra is more resistant. Identification of the mode of resistance may reveal ways in which resistance to twos potted spider mites can be further enhanced.
Document Type: Research Article
Publication date: April 1, 1993
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Journal of Economic Entomology is published bimonthly in February, April, June, August, October, and December. The journal publishes articles on the economic significance of insects and is divided into the following sections: apiculture & social insects; arthropods in relation to plant disease; forum; insecticide resistance and resistance management; ecotoxicology; biological and microbial control; ecology and behavior; sampling and biostatistics; household and structural insects; medical entomology; molecular entomology; veterinary entomology; forest entomology; horticultural entomology; field and forage crops, and small grains; stored-product; commodity treatment and quarantine entomology; and plant resistance. In addition to research papers, Journal of Economic Entomology publishes Letters to the Editor, interpretive articles in a Forum section, Short Communications, Rapid Communications, and Book Reviews.