Temperature and humidity effects on mortality and pre-adult development of two Phytoseiulus persimilis strains (Acari: Phytoseiidae)

Abstract

Laboratory studies showed no differences between a California (CAL) strain and an Israeli (ISR) strain of Phytoseiulus persimilis Athias-Henriot in the age-specific, pre-adult developmental times at 26.7 C, regardless of humidity. Total pre-adult developmental time was significantly less for the ISR strain at 26.7 C and 10 mb VPD, but development of the two strains were the same at 26.7 C and 5 mb VPD. At 32.2 C there were no differences in the pre-adult developmental times. Further studies in-dicated that the lower humidity threshold for this predator is between 10 and 15 mb VPD. At 15 mb VPD, all individuals died in the egg stage, regardless of temperature tested. Data suggested that the ISR strain tested was not high temperature resistant, but was more tolerant of low humidity than the CAL strain.