Acaricidal and biological activities of Titanium dioxide and Zinc oxide nanoparticles on the two-spotted spider mite, Tetranychus urticae Koch (Acari: Tetranychidae) and their side effects on the predatory mite, Neoseiulus californicus (Acari: Phytoseiidae)

[Display omitted] •TiO2 and ZnO nanoparticles are effective against T. urticae mites.•Considerable prolongation effect on mite biology.•T. urticae females produce lesser fecundities and decreased hatchability rates.•Assessed nanoparticles demonstrated less toxicity in N. californicus populations. The excessive application of pesticides raises environmental pollution levels, necessitating the need to identify alternative substances that do not cause ecological damage. In this context, the toxicity and residual efficacy of titanium dioxide (TiO2) and zinc oxide (ZnO) nanoparticles (NPs) compared to abamectin against adult females of T. urticae was evaluated under laboratory and greenhouse conditions. In addition, the effects of tested NPs on the biological parameters of T. urticae as well as their side effects on the predatory mite, Neoseiulus californicus were examined. In laboratory bioassays, LC50 values of TiO2 and ZnO NPs were 5.82 and 7.09 mg L–1, respectively, compared to 4.90 mg L–1 in abamectin 72 hr post-treatment. TiO2 and ZnO NPs had a prolongation effect on both the developmental and reproductive durations with mean life spans of 33.18 ± 0.72 days and 30.53 ± 0.82 days in the case of TiO2 and ZnO NPs, respectively, compared to 24.65 ± 0.53 days in the normal case. Treated T. urticae females produced lesser fecundities (10–22 eggs less than the normal mean) and decreased hatchability rates. The highest mortality percentages in T. urticae populations were 92.4 % and 90.0 % after 24 h of spraying with TiO2 and ZnO NPs, respectively, compared to 98.4 % in abamectin. In contrast, tested NPs demonstrated less toxicity in N. californicus populations with no phytotoxicity on treated leaves. This study is the first in Egypt to investigate the NPs control of T. urticae mites infesting cucumber plants and the effects on their biology and natural enemies.