EFFECT OF TEMPERATURE AND HUMIDITY ON THE DEVELOPMENT OF PHYTOSEIULUS-PERSIMILIS AND ITS ABILITY TO REGULATE POPULATIONS OF TETRANYCHUS-URTICAE [ACARINA, PHYTOSEIIDAE, TETRANYCHIDAE]

The development of Phytoseiulus persimilisAthias-Henriot and the effectiveness of it as a predator of Tetranychus urticae (Koch) were studied at constant temperatures of 15°, 18°, 21°, 24° and 27°C (humidity fluctuations from 60% to 90% R.H.) and at constant humidities of 40% and 80% R.H. at the temperatures 21° and 27°. Optimal temperature for time of development was 27° (at 60%-85% R.H.). A high reduction in egg vitality was recorded at 40% R. H. and 27% At 21° the egg vitality was only slightly lower at 40% R.H. than at 80% R.H. The predator gave control of T. urticae at temperatures from 15° to 27° (humidity fluctuation from 60%-90% R.H.), and the most rapid and efficient control was obtained at 27° (60%-85% R.H.). The predator did not give sufficient control of T. urticae at 27° and 40% R.H. At 21° control of T. urticae was obtained at both 40% and 80% R.H., but the prey population was reduced faster at 80% R.H. than at 40% R.H. © 1979 Le François.