Field measurements of selection for twospotted spider mite (Acari: Tetranychidae) resistance to dicofol in apple orchards.
1991
Martinson T.E. | Dennehy T.J. | Nyrop J.P. | Reissig W.H.
Mortality of Tetranychus urticae Koch resistant or susceptible to dicofol was measured in apple trees to estimate the selective effect of dicofol applications on spider mite populations. Mortality of RR, RS, SS (female), R and S (male) genotypes was measured in six field experiments. An average of 3.9 RR and 3.7 RS mites survived after treatment for every SS female; 3.4 R males survived for each S male. Dicofol resistance was incompletely dominant under field conditions, in contrast with its recessive inheritance in laboratory bioassays. Concentration-response lines were constructed to compare responses of T. urticae to continuous and discontinuous dicofol residues. LC50's were twofold higher (SS) or threefold higher (RS) on discontinuous residues than on continuous residues. Selection resulting from single dicofol applications is discussed in the context of ongoing efforts to establish appropriate acaricide rotations for control of T. urticae.
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