Multiple natural enemies do not improve two spotted spider mite and flower western thrips control in strawberry tunnels

Resumen

Biological control techniques are commonly used in many horticultural crops in Spain, however the application of these techniques to Spanish strawberries are relatively recent. In this study the effectiveness of augmentative biological control techniques to control the two main strawberry (Fragaria ×ananassa Duchesne) pest: the two-spotted spider mite (TSSM), Tetranychus urticae Koch (Acari: Tetranychidae), and the western flower thrips (WFT), Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae), through releases of the predatory mites Phytoseiulus persimilis Athias-Henriot, Neoseiulus californicus (McGregor), Amblyseius swirskii Athias-Henriot (Acari: Phytoseiidae), and Orius laevigatus (Fieber) (Heteroptera: Anthocoridae) were tested. Two-year results on the performance of treatments using combinations of these biocontrol agents are presented. In both years, all treatments resulted in the reduction of TSSM numbers; but no treatment was better than the release of P. persimilis alone (P < 0.05). TSSM suppression varied among crop phases being greater early in the season. None of the treatments reduced significantly WFT numbers (P < 0.05), and the established economic injury level (EIL) was surpassed from March to late April in both years. However, EIL was surpassed less times when treatment included O. laevigatus (2009: 20.7%; 2010: 22.7% of samples). No effect of A. swirskii was observed when this mite was released. Results corroborate that biological control techniques for TSSM and WFT are feasible for high-plastic tunnel strawberries. Under the conditions in our study no additive effects were observed, and there was not advantage in the release of multiple natural enemies.