Sublethal effects of cyetpyrafen and cyenopyrafen on Panonychus citri (Acari: Tereanychidae)

Abstract: 【Objective】Phytophagous mites of the genus Tetranychus and Panonychus are serious pests on plants worldwide. Among these, the citrus red mite, Panonychus citri (McGregor), is one of most no-torious and devastating citrus pest causing a huge fruit yield loss every year. Biological control of P. citri with native predators has been successfully implemented in many orchards, but is still only used on a rather limited scale. Today, caricides are still of utmost importance in the control of P. citri and this is unlikely to change in the near future. In this study, the effects of sublethal concentrations of cyetpyra-fen and cyenopyrafen on P. citri were assessed. The aim of the present study was to evaluate the effect of cyetpyrafen and cyenopyrafen on life parameters based on the concentration-response bioassay of P. citri, and provide a theoretical basis for proper application of two acaricides.【Methods】All of the ex-periments were conducted under laboratory conditions [(26±1) ℃, 14 h∶10 h (L∶D) and (75%±5%)RH]. The fresh and clean citrus leaves were cut into round discs with a diameter of 25 mm and a circle of absorbent cotton strips around the edge to keep moisture, which were used to feed P. citri. Leaf disc bioassay was employed to test the toxicity of cyetpyrafen and cyenopyrafen to P. citri. The sublethal doses of cyetpyrafen and cyenopyrafen (LC10 and LC30) were selected to treat the eggs and female adults of P. citri. After eggs and female adults were exposed to LC10 and LC30 concentration, the development  and fecundity of F0 and F1 generations were evaluated scientifically.【Results】The results of toxicity test showed that the LC50 of cyetpyrafen and cyenopyrafen to P. citri eggs were 11.77 mg·L^-1 and 12.59 mg·L^-1,the LC50 against female adults of P. citri were 1.17 mg · L^{- 1} and 2.01 mg · L^{- 1}, respectively. It indicated that the toxicity of cyetpyrafen and cyenopyrafen to P. citri was strong and the toxicity to female adults was stronger than that to eggs. The nymphal stage of P. citri after F0 generation was significantly short-ened after treatment with sublethal doses of cyetpyrafen LC10 and LC30. The egg stage, larval stage and immature stage of LC10 were significantly shortened after treatment with sublethal doses of cyeno-pyrafen LC10. But the egg stage was significantly prolonged, and the larval and postnymph stages were significantly shortened after treatment with sublethal doses of cyenopyrafen LC30. The results of the four treatments showed that the oviposition period of female adult mites was shortened and the amount of oviposition decreased. In general, the fecundities of the F0 generation of P. citri slightly decreased af-ter eggs and female adults were exposed to LC10 and LC30 concentrations of cyetpyrafen and cyeno-pyrafen for 12 h. When the female adults of P. citri were treated with cyetpyrafen and cyenopyrafen at the doses of LC10 and LC30, the oviposition period, fecundity and longevity of female adults decreased, but not significantly. In F1 generation, the larval stage and prenymph stage were significantly shortened after treatment with sublethal doses of cyetpyrafen LC10 and LC30. There was no significant difference between two treatments of cyenopyrafen and the control except the nymphal stage significantly de-creased before treatment with sublethal doses of cyenopyrafen LC10. The results also showed that the fe-cundity of F1 generation increased significantly and the longevity of adult mites decreased after treat-ment with cyetpyrafen LC10 and LC30. Values of the intrinsic rate of increase (rm) (0.193 1 and 0.190 4)of F1 generation of P. citri treated with sublethal concentrations (LC10 and LC30) of cyetpyrafen were higher as compared with the control (0.156 7). Net proliferation rates (R0) (22.90 and 21.89) of F1 gener-ation of P. citri treated with sublethal concentrations (LC10 and LC30) of cyetpyrafen were higher as com-pared with the control (15.37). Population doubling times (Dt) (3.59 and 3.64) of F1 generation of P. citri treated with sublethal concentrations (LC10 and LC30) of cyetpyrafen were lower as compared with the control (4.43). There was no significant difference in fecundity per female compared with the con-trol between LC10 and LC30 treatments with cyenopyrafen, but the longevity of female adults decreased significantly. F1 generation of P. citri exposed to sublethal concentrations (LC30) of cyenopyrafen for 12 h had almost the same rm (0.162 7) value as the control, but F1 generation of P. citri had increased rm(0.179 8) value as compared with the control after exposed to sublethal concentrations (LC10) of cyeno-pyrafen for 12 h. The Dt (4.28) of F1 generation of P. citri treated with sublethal concentrations (LC30) of cyenopyrafen was similar to the control, but the Dt (3.86) of F1 generation of P. citri treated with sub-lethal concentrations (LC10) of cyenopyrafen was lower as compared with the control.【Conclusion】Cy-etpyrafen and cyenopyrafen had a low-dose-stimulating effect on P. citri, and both played a certain role in facilitating the development of future populations, which was of significance in developing integrat-ed pest management (IPM) strategies. But the proliferation of P. citri was reduced without effect at high concentration of cyenopyrafen.