1991 Volume 35 Issue 2 Pages 153-159
The seasonal occurrence of Tetranychus kanzawai KISHIDA and two of its predators were studied in an open eggplant field which had been sprayed periodically with each of three synthetic pyrethroids (SP; fenvalerate, permethrin, and fenpropathrin) over about 5 months. The occurrence was compared with the occurrence in fields sprayed with an organophosphorus insecticide (fenitrothion) and or an acaricide (fenbutatin oxide), and in fields that were not sprayed. The mite populations exhibited 3-4 distinct peaks in plots sprayed with fenvalerate or permethrin, and 2-3 peaks in plots sprayed with fenpropathrin about 20 days after spraying. The peak densities in August in the SP plots reached 1, 000-3, 000 adult females per plant, which were much higher than in fields that were not sprayed and in those sprayed with other pesticide(s). The dominant predators in this eggplant field were the phytoseiid mite, Amblyseius longispznosus (EVANS), and the anthocorid bug, Orius sp. In the SP plots, the densities of these predators remained much lower throughout the study period and increased much less in response to increases in mite density than in the other plots, although the density of Orius sp. was relatively high in plots sprayed with fenpropathrin. These results clearly show that the mite outbreaks occurred because of the adverse effects of the SP sprays on the mite predators.
