Potential of predation byMetaseiulus occidentalis in compensating for increased,nutritionally induced,power of increase ofTetranychus urticae

This study was conducted to ascertain if the predatory phytoseiidMetaseiulus occidentalis (Nesbitt) could contain and regulate a prey population of the two-spotted mite,Tetranychus urticae Koch, on strawberries at both high and low levels of reproductive increase of the prey species, by use of high and low levels of nitrogen fertilization of the strawberry plants which were grown in 2 hydroponic tanks, 1 with full nutrients, 1 with 1/40 full nutrients. A 14-h day length was provided. Temperatures averaged 21°C with R.H. averaging about 75. After inoculation prey and predator counts were made weekly. Fecundity tests were conducted throughout the experiment as were leaf analyses to determine the levels of available nutrients. The phytoseiid gave good control of the spider mite population in spite of (compensating for) an increase in fecundity due to the high nutritional qualities of the host plant over a relatively long period of time. The results showed the numerical response of the predator to be sufficient to respond to and control the prey population under both high and low fertilization, althougheconomic control was less reliable under high nitrogen.