There is, however, an enigma in all of this:

> [There has been] a decline in tracheal mite prevalence since introduction into the US.  This may indicate that current control and resistance techniques are effective in reducing the pest population or that the pest population is declining for some other reason.  

> However high winter loss rates in the last decade and limited infection data leaves conclusions of the current damage caused by tracheal mites to be unknown. Current systematic honey bee pest surveys by USDA-APHIS do not measure tracheal mite prevalence.

Authors: Philip A. Moore, Michael E. Wilson, John A. Skinner, Department of Entomology and Plant Pathology, the University of Tennessee, Knoxville TN

As they say, there may be "some other reason."
PLB

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