INFLUENCE OF TEMPERATURE AND VAPOR-PRESSURE DEFICIT ON THE RATE OF PREDATION BY THE PREDATORY MITE, AMBLYSEIUS-CUCUMERIS, ON FRANKLINIELLA-OCCIDENTALIS

The influence of temperature and vapor pressure deficit (VPD) on the r ate of predation by the predatory mite, Amblyseius cucumeris (Oudemans ) on Frankliniella occidentalis (Pergande) was determined under contro lled laboratory conditions. The survival of first instars of F. occide ntalis was initially determined by themselves. Then the number of firs t instars that were killed by a single female adult of A. cucumeris wa s determined for the same density of thrips. The differences in the mo rtality between the two experiments were used to calculate the rate of predation by A. cucumeris under a range of temperature and VPD regime s. Rate of predation was expressed as the number of thrips killed per h to account for the different time periods that the trials lasted. A quadratic model was fitted to the data. At a constant temperature, the rate of predation decreased with increasing VPD for VPDs less than or equal to 1.24 to 1.44 kPa. Above these VPDs, the rate of predation st arted to increase again. At a constant VPD, the rate of predation decr eased slightly at the lower temperatures and increased at the higher t emperatures. The rate of change was dependent upon the VPD. By using t he quadratic model, the rate of predation can be predicted for the ran ge of hygrothermal conditions that would be encountered in the greenho use. The optimal condition for maximum rate of predation by A. cucumer is on first instars of F. occidentalis in the greenhouse is a VPD less than or equal to 0.75 kPa at the recommended production temperatures and VPDs (17 to 25 degrees C and less than or equal to 1.5 kPa).