Biological control of Tetranychus urticae (Koch) (Acari: Tetranychidae) in southern New South Wales peach orchards : the role of Amblyseius victoriensis (Acarina: Phytoseiidae)

Populations of mite predators and Tetranychus urticae (Tetranychidae) occurring in peach orchards on two farms at Leeton, New South Wales, were monitored during 1987/88. In both orchards the key pest Cydia molesta (Busck) (Tortricidae) was controlled by a pheromonal mating disruption strategy which avoided the use of broad-spectrum insecticides. During both years substantial populations of a native predatory mite, Amblyseius victoriensis were associated with an absence or very low populations of T. urticae from mid-summer until leaf fall. During spring 1987 some control of T. urticae was provided by a suite of predatory insects. Late spring applications of fungicide delayed development of A. victoriensis populations and a mid-summer miticide spray delayed establishment of the predator. Typhlodromus occidentalis occurred only when A. victoriensis populations were low or eradicated by sprays. During autumn, 1987 A. victoriensis occurred on orchard weeds but populations declined to a low level during winter. Substantial overwintering populations of reproductive T. urticae occurred on weeds and invaded the trees at bud burst. The generalist feeding behaviour of A. victoriensis is considered to be the key to the success of this predator. Dependence on biological control for T. urticae management is considered to be a practical option for southern New South Wales peach orchardists.