A dual-isotope porometer measured gas-exchange rates on almond leaves exposed to feeding damage byPanonychus citri, P. ulmi, Tetranychus pacificus, orT. urticae. The feeding injury of all four mite species caused significantly lower rates of stomatal conductance, mesophyll conductance, and photosynthesis compared with undamaged controls. No significant differences in gas-exchange rates occurred between species within either genus; however, significant differences between genera were detected.Tetranychusspp. caused lower rates of mesophyll conductance and photosynthesis when compared withPanonychusspp.