Acaricidal Activity of UV-C irradiation on Tetranychus urticae and eggs using pulsed krypton fluoride excimer laser

Abstract

Background While pulsed UV-C light sources such as excimer lasers are used in emerging non-thermal food decontamination method, they also have a high potential for a wide range of other microbial decontamination applications. The acaricidal effect of an experimental UV-C irradiation device was assessed using two-spotted spider mite female adults Tetranychus urticae and eggs as a model. Methods The UV-C light source was generated by a pulsed krypton fluoride (KrF) excimer laser operating at 248 nm emission wavelength. Pulse energy and pulse repetition rate were 5mJ, and up to 100Hz rate, respectively. Distance from light source to target was 150 mm with a target surface of 21.6 cm². The exposure time of the mite and fresh eggs varied from 1 to 4 minutes at a power of 300 mW. The post-irradiation acaricidal effects (mites’ mortality) were assessed immediately and measured 24 h post-irradiation. Effects on the hatchability of irradiated eggs were observed daily post-irradiation for up to 12 days. Results The mortality of mites observed with an energy amount of 5 and 40 mJ/mm² was 26% and 90%, respectively. The mortality at 80 mJ/mm² reached 99%. The effect of exposure duration on mortality was minimal. The effect of irradiation of eggs hatchability was even more important, with about 100% mortality with as little as 5 mJ/mm² for each exposure time. Conclusions A high mite mortality and lethal egg damage was already observed after less than 1 min exposure to UV-C pulsed irradiation. Pending further developments and feasibility studies, the current results and features of the UV-C generator (energy output modulation and applicability to varying spot sizes) open up a large field of germicidal applications requiring long-range radiation.