Predation by Neoseiulus cucumeris on western flower thrips, and its oviposition on greenhouse cucumber under winter vs. summer conditions in a temperate climate

In short-term controlled chamber experiments, the influence of light intensity, photoperiod, temperature, and light vs. dark conditions within the diel cycle were investigated on the predation and oviposition rates of Neoseiulus cucumeris (Oudemans) (Acari: Phytoseiidae), a biological control agent commonly used in greenhouse crops worldwide. In a 2 × 2 factorial experiment, neither light intensity nor photoperiod had an effect on the number of thrips killed by N. cucumeris at 24 °C. Light intensity, but not photoperiod, had an effect on the number of eggs laid, with more eggs laid at high (83.0 ± 1 Wm−2) than low (11.1 ± 0.5 Wm−2) light intensity at 24 °C. When simulated seasonal light regimes were compared (summer: high light intensity, long daylength vs. winter: low light intensity, short daylength) at the 2 constant temperatures 20 °C vs. 24 °C, only temperature had an effect. Significantly more thrips were killed at 24 °C than 20 °C irrespective of light regime, which is consistent with light having had no effect in the light intensity × photoperiod assay. There was no significant difference in the predation rate on first instar WFT by starved female N. cucumeris during scotophase vs. photophase when raised either under long L16:D8 h or short L8:D16 h diel cycle. However, N. cucumeris females only laid eggs during the photophase, regardless diel cycle in which they were reared. In the winter season, reduced predation by N. cucumeris appears to be influenced more by cooler temperature, than low light intensity and/or short days alone. However, our results also indicate that poor or delayed establishment and numerical response of N. cucumeris in the winter in northern temperate zones in greenhouses under natural light may result from reduced reproductive rate under low light intensity and short daylight conditions.