INDICATOR PLANTS FOR MONITORING PEST POPULATION-GROWTH

Some plants are more attractive to agricultural pests than the crop to which they are a pest. The use of these plants as indicator plants to monitor pest populations is examined. Bean plants were found to be ef fective indicators for forecasting the growth of carmine spider mite, Tetranychus cinnabarinus (Boisduval), on greenhouse tomatoes, Lycopers icum esculentum L. Spider mite population growth rates were the same o n both host plants, but because they became established up to 5 wk ear lier on beans, Phaseolus vulgaris L., monitoring carmine spider mite p opulation growth on beans provides enough time to order and distribute natural enemies for their control on tomatoes. The oviposition and de velopmental rates of mites did not differ on the 2 host plants. Howeve r, the temperature threshold for oviposition was 7 degrees C lower on beans than tomatoes, resulting in earlier establishment and onset of p opulation growth in the spring on the indicator plants. The potential for using indicator plants to establish biological control agents was investigated with the predatory mite Phytoseiulus persimilis Athias-He nriot. P. persimilis became established equally well when broadcast on the crop (with its much lower prey population density) as when releas ed only on infested indicator plants. Best control of carmine spider m ites by Phytoseiulus was obtained when the predators were released whe n spider mite density reached 12 per tomato leaf, which occurred when the mite density on beans was 100 per leaf, 5 wk after reaching 12 mit es per bean leaf. Acting on this threshold, a grower would have ample time to order, receive, and release predatory mites. Predation of spid er mites by Phytoseiulus was higher on the tomatoes than the beans. Ph ytoseiulus populations dipped after introduction on both host plants b ut recovered more rapidly on beans. The different predation and surviv al rates on the 2 host plants probably served to keep the 2 population cycles on the 2 hosts out of synchrony, thereby sustaining the popula tion interactions.