Crosses between femaleTetranychus urticaeKoch and males of 7 other tetranychid species showed that the cross withT. cinnabarinus(Boisduval) was the only one that resulted in sterile hybrids. Moreover, any production of progeny from subsequent matings was blocked by the initial interspecific mating. WhenT. urticaeandT. cinnabarinusmales were placed withT. urticaefemales in a 1:1 ratio, theT. urticaemales mated first 70.6% of the time. All interspecific mating resulted in a reduction in egg deposition. Four inundative releases ofT. cinnabarinusmales at 4-day intervals into an established population ofT. urticaeproduced marked suppressive results.