Inheritance of Early-Stage Resistance to Formetanate and Cyhexatin in Tetranychus urticae Koch (Acarina: Tetranychidae)

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Abstract
Populations of Tetranychus urticae (Koch) from strawberry and pear in the western United States showed high to moderate levels of resistance to formetanate (117-fold) and cyhexatin (17-fold) at the 50% lethal concentration and 117-fold and 171-fold at the 95% lethal concentration, respectively. Inheritance of formetanate resistance appears to be dominant and monofactorially determined, whereas cyhexatin resistance in T. urticae may be intermediate to recessive in dominance. The mono- or polygenic nature of cyhexatin resistance could not be determined, because the levels of resistance are still too low for discriminatory analysis using standard backcrossing tests. The implications of these features of inheritance of acaricide resistance to management of field populations of T. urticae are discussed.