LONG-TERM STABILITY IN THE INTERACTION BETWEEN TETRANYCHUS-URTICAE AND PHYTOSEIULUS-PERSIMILIS PRODUCING SUCCESSFUL INTEGRATED CONTROL ON ROSES IN SOUTHEAST QUEENSLAND

Phytoseiulus persimilis Athias-Henriot successfully controlled Tetranychus urticae Koch on rose hedges in an integrated mite control programme in two unheated plastic-covered tunnels at Cleveland in southern Queensland. Mite populations were monitored fortnightly for nearly three years in one tunnel and for two years in a second. Once established, P. persimilis quickly suppressed T. urticae and then persisted. A relatively stable, long-term, low-level interaction developed between the two species under normal commercial conditions. In one tunnel, the production (upper) level of the four rose hedges contained fewer mites of both species per compound leaf (1.71 of all stages of T. urticae, 0.38 motiles; 0.25 of all stages of P. persimilis, 0.12 motiles) than the maintenance (lower) layer (2.02 of all stages of T. urticae, 0.75 motiles; 0.35 of all stages of P. persimilis, 0.21 motiles). On 68% of sampling occasions, 10% or less of compound leaves in the production layer were infested with T. urticae (all stages including eggs) and control was excellent throughout the 30-month period after P. persimilis was established, there being no economic losses. In the second tunnel, there was no significant difference between mite numbers in the production and maintenance layers of the two hedges examined. The overall mean number of all stages of T. urticae per compound leaf was 3.2 (1.45 motiles), and of P. persimilis 0.46 (0.25 motiles). Control here was slightly less effective than in the first tunnel, but was still satisfactory, with 10% or less of leaves being infested on 45.5% of sampling occasions (20% or less on 66% of sampling occasions) with T. urticae (all stages including eggs). Phytoseiulus persimilis was not reintroduced or redistributed during the course of the observations. An auxiliary miticide (clofentezine) was applied on only one occasion to selected areas in the second tunnel. The influence of high temperatures on control by P. persimilis is discussed.