Predation efficiency of predatory mites from different climatic origin under variable climates in Belgian greenhouses

Abstract: In order to better adapt the use of predatory mites with the modern greenhouse climate regulation strategies, functional response models were constructed to demonstrate the impact of realistic climate variations on the predation efficiency on Tetranychus urticae eggs by Neoseiulus fallacis, Phytoseiulus persimilis and N. californicus predatory mites (Acari: Phytoseiidae).First, two T regimes were compared at 70% RH and 16 L:8 D photoperiod: DIF 0 (constant T) and DIF 15 (variable T with a day-night difference of 15 °C). At mean T of 25 °C, DIF 15 reduced the predation efficiency of P. persimilis and N. californicus compared to DIF 0. At the lower mean T of 15 °C, however, N. californicus had a higher predation efficiency at DIF 15. The predation efficiency of N. fallacis was similar at DIF 15 and DIF 0 irrespective of the mean temperature.Secondly, two RH regimes were compared, at constant T of 25 °C and constant photoperiod (16 L:8 D): RHCTE (constant 70% RH) and RHALT (alternating 40% L:70% D RH). P. persimilis and N. fallacis predated better at RHCTE than RHALT, but for N. californicus the opposite was true. The used strain of N. californicus is more adapted to periods of low RH as P. persimilis or N. californicus.Thirdly, a summer regime (mean T of 25 °C, RH alternating 40% L:70% D and photoperiod 16 L:8 D) and winter regime (mean T of 15 °C, RH 70%, photoperiod 8 L:16 D) were evaluated. Under summer regimes, DIF 15 influenced the predation efficiency of P. persimilis and N. californicus negatively as compared to DIF 0. Under winter regimes, DIF 15 influenced predation efficiency of N. californicus and P. persimilis positively as compared to DIF 0. DIF had no influence on N. fallacis under winter and summer regimes.We conclude that N. fallacis originating from temperate climate is less influenced by variable greenhouse climates compared to P. persimilis and N. californicus that originate from warmer and drier regions. For optimal control efficiency, predatory mites should be chosen by taking into account the actual greenhouse climate and the climate in the predatory mite’s region of origin. Research is ongoing to validate this hypothesis for other commercially used predatory mites.