Population growth and predation interference between two species of predatory phytoseiid mites (Acarina:...

Populations of two species of phytoseiid mite predators, Phytoseiulus persimilis Athias-Henriot and Amblyseius degenerans (Berlese), feeding on a tetranychid prey, Tetranychus pacificus McGregor, were allowed to grow separately as well as together on bush lima bean (Phaseolus lunatus Var.) arenas in the laboratory. The population plateau attained by P. persimilis was nearly 5 times higher than that for A. degenerans when each species was on separate leaf arenas. When they were on the same arena, P. persimilis was outcompeted by A. degenerans after about 70 days of population growth. When dispersal to other arenas was necessary for the predators to find prey in another experiment, P. persimilis survived well but not A. degenerans. The mechanisms underlying species displacement were explored further. The differential mortality of immature predators at different developmental stages due to interspecific predation was concluded to be responsible for the population decline of P. persimilis, and the decline of A. degenerans in another experiment was attributed to its sedentary tendency regardless of prey distribution and to the lack of alternative food sources in the system. The implications to biological control of mutual predation between predator species is discussed briefly.