The effects of temperature and humidity on the development of Oligonychus coffeae (Nietner) were studied by exposing the various stages of the mite to air in equilibrium with saturated solutions of appropriate salts in containers within thermostatically controlled cabinets. Adults and early stages were maintained on fresh tea shoots.

The pre-oviposition, oviposition and post-oviposition periods of adult females at 75–80% relative varied inversely with temperature, and averaged, respectively, 0.8, 5.9 and 1.4 days at 32° and 2.3, 30.6 and 2.0 days at 20°C. The mean number of eggs laid per female likewise varied inversely with temperature, from 12.0 at 32°C at 32° to 107.3 at 20°C.

No eggs hatched when incubated at 34°C., irrespective of humidity, or at 17% R.H., irrespective of temperature. Optimum conditions for incubation (those affording over 90% hatch) were provied by a combination of temperatures and relative humidities within the ranges 20–30°C. and 49–94%. When eggs were exposed daily for five days to temperatures of 37 or 40° for six hours at 72–94% R.H. and then transferred to room conditions (24–32°C., 64–88% R.H.), the percentage of eggs hatching was reduced from 94.7 (room conditions) to about 75 or 5–12, respectively.

The mean incubation period of eggs varied from 3.9 days at 32° to 10.8 at 20°C., and the mean duratio of the combined larval and nymphal stages from 4.9 days at 30° to 8.7 at 20°C. At 32°C., larval mortality was very high.