Resistance of Cotton, Gossypium hirsutum L., to Natural Field Populations of Twospotted Spider Mites (Acari: Tetranychidae)1

Abstract

Natural populations of twospotted spider mites, Tetranychus urticae Koch., infested cotton, Gossypium hirsutum L., in genetic studies in 1980 at three locations near Stoneville, Miss. There were significant differences in spider mite numbers between genotypes. The phenotyphic ranges in spider mite counts per 6.5 cm² of leaf surface were: test I, 3.9 to 1.4; test II, 12.3 to 6.4; and test III, 4.9 to 3.7. Genotypes developed in the Mississippi delta had the lowest populations of spider mites. Cottons which tended to have high population numbers were Camd-E, Coker 76-118, MO 311, MO 73-1203, UGA 220, TH 149, Delcot, and Coker 201. Okra-leaf cotton had significantly fewer spider mites than frego bract, smoothleaf (Sm₂), nectariless, glandless, and normal isolines. Correlation analyses of interest in test I were: spider mites with yield, percent first harvest, and yield first harvest, r = −0.55*,0.58*, and 0.25, respectively. In test II, correlations were: r = −0.47*, 0.66** and −0.07, respectively, for yield, percent first harvest, and yield first harvest. Yield data were not obtained from test III.