Total effects of selected plant protection products applied to different natural substrates on the predatory mite Typhlodromus pyri Sch.

Abstract: Extended laboratory studies were conducted to evaluate lethal and sublethal effects of selected plant protection products (PPPs) on Typhlodromus pyri Sch. (Acari: Phytoseiidae). The endpoints of the studies were mortality after 7 days of exposure and the reduction in total egg production after 14 days. Three fungicides (thiophanate-methyl, chlorothalonil, and pyrimethanil), one insecticide/acaricide (paraffin oil), one plant growth regulator (ethephon), and three herbicides (MCPA, clopyralid + picloram, and amidosulfuron) were tested using commercial products at their maximum recommended rates. The studies were performed according to the ‘island method’ (Joisten, 2000). T. pyri protonymphs were exposed on the following natural substrates: bean (Phaseolus vulgaris), rose (Rosa L.), and blackberry (Rubus L.) treated with the PPPs with the help of the Potter laboratory spray tower on the basis of the application of 200 l of water/ha. Due to phytotoxic effects of MCPA and clopyralid + picloram, they were applied to rose and blackberry leaf discs, whereas bean leaf discs were sprayed with the remaining PPPs. A control (distilled water) and a reference item treatment were also included. Total effects (E) of the tested PPPs on T. pyri were determined by combining lethal (mortality) and sublethal effects (reproduction) using the IOBC classification. Thiophanate-methyl, chlorothalonil, paraffin oil, and MCPA appeared to be slightly harmful, whereas the remaining PPPs were found to be harmless to T. pyri. Among all the PPPs evaluated, ethephon was the most selective to the predators. None of the PPPs adversely affected the reproductive capacity of the mites. The poorest reproductive performance was caused by thiophanate-methyl (the reduction of 39.5%).