| It is important for selecting safer and more efficient agents and rational use of pesticides to evaluate the sublethal effects of pesticides on insects or mites. Tetranychus cinnabarinus (Boisduval) is a main worldwide pest mite, which can develop resistance to many acaricides quickly. So resistance risk assessment of acaricides becomes a research focus in recent years, and sublethal effects are very important contents, which play a key role in quantitative control of mite population. Scopoletin, a plant secondary metabolite, which has broad prospect on development and application of botanical acaricides. However, reports about acaricidal activity of scopoletin were limited to a certain degree of contact and systemic activities. To our best knowledge, there are no reports about sublethal effects on mite population. In this paper, LCio, LC20, LC30, LC40and LC50were selected as sublehal dosages. The sublethal effects of scopoletin against T. cinnabarinus population were carried out by the life table technique and the population parameters were caculated according to the specific formula. This paper aimed to evaluate system influence of scopoletin on population of T. cinnabarinus at sublethal dosages, and provide the theoretical basis for the further development and application of scopoletin used as a plant-derived acaricide. Main results are as follows:1Sublethal dosages of scopoletin on the experimental population of T. cinnabarinusThe contact activity of scopoletin against female adults of T. cinnabarinus was evaluated in this paper. The LC-P equation at48h after treatment was y=-2.8572+1.1551x, r=0.9523. The LC50values was0.2975mg-mL-1,95%confidence intervals was0.1550～0.6730mg-mL-1. The LC40、 LC30、LC20and LC10values at48h after treatment were0.1795、0.1046、0.0556and0.023mg-mL- respectively.2Repellent and oviposition deterrent activities of scopoletin against T. cinnabarinus at sublethal dosagesT. cinnabarinus were treated with sublethal dosages, there was not only a lethal effect on population, but also effects on distribution of population and oviposition. The method of choice and no choice were used to measure repellent and oviposition deterrent activities against female adults of T. cinnabarinus, respectively. At LC50、LC30and LC10, the rates of mite in the treatment and control areas were about50%; at LC50and LC10, scopoletin showed oviposition deterrent effect, and the average oviposition inhibition rates were23.02%and13.23%, while LC30was-8.25%, suggested stimulation effect on oviposition of female adults, it may be caused by acaricide hormesis.3The sublethal effects on development and reproduction of scopoletin against T. cinnabarinusThe effect of scopoletin on population of T. cinnabarinus was used leaf disk feeding method. Scopoletin can stimulate oviposition of female adults of T. cinnabarinus, prolong longevity and oviposition duration and increase sex ratios. The fecundity of female adults treated with scopoletin at three sublethal dosages (LC40, LC30and LC20) was increased by73.82%,186.97%and70.18%, respectively. The longevity and oviposition duration of female adults treated with scopoletin at higher concentrations (LC40and LC30) were obviously longer than those of control, oviposition duration was prolonged by8.30%and11.90%, and longevity was prolonged by14.91%and31.03%. Sex ratios increased a little, but all were between4and5, with no great fluctuations.4The sublethal effects on population parameters of scopoletin against T. cinnabarinus in the F1generationThe effects on development period and reproduction of scopoletin against T. cinnabarinus in the F1generation were determined. The duration of oviposition, larval and nymphal stages were not significantly different from the control (P>0.05), but the adult period and female longevity were shorter than those of the control. The F1generation had shortened oviposition duration, reduced fecundity and decreased sex ratios when compared with the control.The life tables of experimental population of T. cinnabarinus F1generation treated with scopoletin at sublethal dosages were established and analyzed. Parameters such as the intrinsic rate of increase, net production rate, finite rate of increase, mean generation time change with concentrations of scopoletin. The net reproductive rate (Ro) dropped from50.5976to33.9910, the mean generation time (T) and population doubling time (Dt) were all shorter than those of the control, and fitness defects appeared in three treatment populations. The results indicate that scopoletin can reduce the development and reproduction rates of T. cinnabarinus populations treated at sublethal dosages, which provide positive evidence for application of scopoletin in pest management. |
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