Date Published: November 5, 2018
Publisher: Public Library of Science
Author(s): Jingqi Ouyang, Yajing Tian, Chunxian Jiang, Qunfang Yang, Haijian Wang, Qing Li, Yulin Gao.
Tetranychus cinnabarinus (Boisduval) is an agricultural mite pest threatens crops throughout the world, causing serious economic loses. Exploring the effects of acaricides on predatory mites is crucial for the combination of biological and chemical control of T. cinnabarinus. Neoseiulus californicus (McGregor) is one of the principal natural enemies of T. cinnabarinus, which can be applied in protected agriculture. In this study, the effects of sublethal concentrations of a new acaricide, SYP-9625 on two mite species, and the effects of the application concentration on predatory mite, N. californicus were assessed. The aim of the present study was to evaluate the effect of SYP-9625 on life parameters and predation capacity of N. californicus based on the concentration-response bioassay of T. cinnabarinus to explor the application of the new acaricide with natural enemy N. californicus.
All of the experiments were conducted under laboratory conditions [25 ± 1°C, 16: 8 h (L: D) and 75 ± 5% RH]. The sublethal concentrations LC10 (0.375μg/mL) and the LC30 (0.841μg/mL) against T. cinnabarinus and the application concentration (100μg/mL) against N. californicus were used to evaluate the effects of SYP-9625 on population parameters of N. californicus based on an age-stage, two-sex life table and its predation capacity by functional response.
cinnabarinus females treated with LC30 exhibited significantly reduced net reproductive rates (R0 = 11.02) in their offspring compared with females treated with LC10 (R0 = 14.96) and untreated females (R0 = 32.74). However, the intrinsic rate of increase (rm) and the finite rate of increase (λ) of N. californicus indicated that the application concentration of SYP-9625 had no significant negative effect on N. californicus eggs (rm = 0.277, λ = 1.319) compared to the control (rm = 0.292, λ = 1.338). Additionally, most population parameters of N. californicus showed a dose-dependent manner with the increase of the concentration of SYP-9625 against T. cinnabarinus. SYP-9625 also stimulated the control efficiency of N. californicus against immobile stages including eggs and larvae.
This study demonstrated that sublethal concentrations of SYP-9625 can inhibit the population growth of T. cinnabarinus. In addition, the sublethal concentrations and the application concentration showed no effect on the population growth of N. californicus. These two advantages described above showed great commercial potential of this new acaricide based on population parameters of the two mite species and predation capacity of the predatory mite under laboratory conditions.
Nowadays, agricultural spider mite pests are becoming one of the major threats to some important crops such as vegetables, fruits and ornamentals throughout the world. Most spider mite pests, such as Tetranychus cinnabarinus (Boisduval), have gained rapid resistance resulting from frequent applications of acaricides [1, 2]. Therefore, new acaricides with excellent insecticidal activity and low toxicity to natural enemies are becoming necessary .
In previous studies, many species of natural enemies and pesticides have been tested so far to corroborate the combination of chemical and biological control agents under laboratory conditions [38–42]. Moreover, numerous studies have focused on the importance of sublethal effects of pesticides on predatory mites [3, 9, 33]. On one hand, this is the first report on both pest mites and the predatory mites of the new pesticide SYP-9625. On the other hand, N. californicus provides good efficacy against pest mites as showed by most studies [15, 43]. Therefore, this study was designed to examine the appropriate concentration of SYP-9625 that can be used to control the increasing population of T. cinnabarinus effectively and simultaneously protect N. californicus.
The sublethal effects of SYP-9625 on T. cinnabarinus, the effects of application concentration of SYP-9625 on the predatory mite N. californicus and the functional response of N. californicus were successfully assessed. This study concludes that SYP-9625, particularly at a lower concentration (LC10 = 0.375 μg/mL) can effectively control the increasing population of T. cinnabarinus and stimulate the predation capability of N. californicus. We confirmed that the new acaricide SYP-9625 can be used in concert with the release of the predator N. californicus in IPM.