Effect of temperature and humidity on the development ofPhytoseiulus Persimilis and its ability to regulate populations ofTetranychus urticae [Acarina: Phytoseiidae. Tetranychidae]

The development ofPhytoseiulus persimilis Athias-Henriot and the effectiveness of it as a predator ofTetranychus 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 ofT. 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 ofT. urticae at 27° and 40% R.H. At 21° control ofT. 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.