The dynamics of two species of predatory mites (Acarina

ABSTRACT The objectives of this study were to investigate how predatory mites of two phytoseiid species (Acarina: Phytoseiidae) could be directly affected by the presence of conspecifics or heterospecifics sharing the same habitat in the laboratory. The biological characteristics of the adult females of Phytoseiulus persimilis Athias-Henriot and Amblyseius degenerans (Berlese) feeding on tetranychid mites (Tetranychus pacificus McGregor) were examined in single and two-predator systems. The two predatory competitor species were characterized by their body weight, time budgets, capacity for predating the immatures of their own and the rival species, behavioural response to prey cues and population growths. Two types of interference competition which might occur in the acarine system were demonstrated experimentally. These included : 1) interference in food consumption and 2) intra- or interspecific predation between competitors. The effects of the two types of direct competition on the growth of competing populations and on the prey resource were examined theoretically with the general population model proposed in this study. The properties of the interactive system for two specialist predators as well as a specialist and a generalist predator to coexist on a common resource were explored. It was shown that interference competition between consumer species had a profound impact on their coexistence and also on the prey resource. The present investigation contributes to a broader understanding of the biological characteristics of two phytoseiid predators in interactive systems. It also provides a theoretical basis towards the clarification of the controversial issue concerning the releasing of single vs. multiple species of predators as control agents in the biological control of pests.