ABSTRACTPapaya (Carica papaya L.) is an important crop in all tropical countries including Mexico. Tetranychus merganser Boudreaux was recently detected in Mexico, and represents a potential threat to papaya production. There is little available information on this mite; therefore, research on this species is urgently required. We undertook a series of experiments to assess the effect of different initial densities of T. merganser on the level of leaf damage and photosynthetic activity of papaya; evaluations were made 21, 42 and 63 days after the experiments were initiated. We found that the greatest damage caused by T. merganser occurred after the final sampling time (63 days), regardless of the initial density of T. merganser; there were no differences among treatments in photosynthetic activity or chlorophyll content. We also evaluated how introduction of the generalist mite predators, Amblyseius swirskii Athias-Henriot (Gamasida: Phytoseiidae) or Neoseiulus californicus McGregor (Gamasida: Phytoseiidae), affected the relationship between the level of leaf damage and final densities of T. merganser at the end of the experiment. The introduction of predators resulted in a significant decrease in T. merganser densities. The need for early detection of this pest to reduce damage, and achieve the greatest impact of biological control is discussed.