Plasma-activated water irrigation increases mortality of immature spider mites (Tetranychus urticae) on tomato plants.

Supplementary irrigation with plasma-activated water (PAW) has been shown to boost seed germination and seedling vigor, and it has the potential to induce host plant resistance against pest populations, such as, two-spotted spider mites (TSSM) (Tetranychus urticae Koch). However, there is limited knowledge about the relative susceptibility of TSSM life stages to supplementary PAW irrigation. Here, we used age two-sex life table analysis to examine demographic parameters on leaf discs from control tomato plants (no PAW irrigation) and from plants receiving supplementary PAW irrigation, PAW1 and PAW2 (treatment of water for 6.0 and 9.4 min with atmospheric plasma jet respectively). Immature TSSM mortality was significantly higher on PAW1 (52%) and PAW2 (26%) treatments compared to control (6%). Immature developmental duration, adult pre-oviposition period and total pre-oviposition periods, adult longevity, fecundity, and sex ratio were all significantly reduced in response to PAW irrigation. Life table analyses showed that intrinsic rate of increase (r), net reproductive rate (R), and finite rate of increase (λ) were significantly reduced on leaf discs from PAW-irrigated plants compared to control. Population modeling over a 60-day time showed a 10-11-fold reduction in TSSM populations on PAW-irrigated plants compared to control. These findings confirm the suppressive effects of supplementary PAW irrigation on TSSM population dynamics. Furthermore, results support the hypothesis that early-stage susceptibility, prolonged developmental times of individual life stages, and reduced fecundity are key factors driving PAW-based suppression of TSSM population dynamics. Thus, we conclude that supplementary PAW irrigation should be considered a potential component of long-term and sustainable pest management against TSSM and other major crop pests.