| The carmine spider mite, Tetranychus cinnabarinus (Boisduval), has a world-wide distribution and is one of the most important agriculture pests. The abuse of chemical acaricide has led to rapid development of resistance in this mite. In our study, strains of Beauveria bassiana were screened for pathogenicity against T.cinabarinus and protect Amblyseius cucμmeris (Acari:Phytoseiidae) in laboratory bioassays. Furthermore, we evaluated the effect of B.bassiana on T.cinabarinus’s mortality, developmental duration and fecundity. Also, we assessed the effect of B. bassiana on A. cucμmeris’s fecundity, developmental duration and functional response, aims to provide a theoretical basis about fungi and predator mite to control T.cinabarinus. The main results obtained are as follows:1. Fifteen strains of B. bassiana were screened for pathogenicity against the carmine spider mite, T.cinnabarinus, in laboratory bioassays. In the first screening, strains of B. bassiana were applied at a single concentration of1×107conidia/mL on female adult. A corrected mortality mite percentage between18.7～83.8%was observed, the median lethal times ranged between4.4～11.7days, with eight strains causing corrected mortality levels higher than50%. The eight most virulent strains were tested their pathogenicity on eggs with three concentrations (1×106;1×107and1×108conidia/mL). Mortality of eggs indicated that Strain Bb2170, Strain Bb0062and Strain Bb025were the most efficient, causing egg mortality of>50%,9days after inoculation, at the highest concentration. In the second screening, the eight most virulent strains were tested their pathogenicity to A.cucμmeris with a single concentration of1×107conidia/mL on female adult. Mortality of predator mites (2.4～22.0%) indicated that all of the eight strains were low insecticidal against A. cucμmeris. Therefore, the first and second screening bioassay indicated that strain Bb025has a highly pathogenicity to T. cinnaberinus, meanwhile, it was low insecticidal to A. cucμmeris. These findings show the potential use of A. cucμmeris in combination with B. bassiana for the biocontrol of T. cinnabarinus.2. A B.bassiana strain Bb025was assayed for its virulence against the larve, nymph and female adults of T.cinnabarinus by spray method at the concentration from1.0×104to1.0×108conidia/mL. The mortality of T.cinnabarinus had a positive correlation with concentration of spore suspension and inoculation time. With the same concentration and inoculation time, female adult’s mortality is the highest and larve mite’s mortality is the lowest. A time-dose-mortality model was used to analyze the bioassay data and the model fitted the data well, resulting in parameters for estimating the time and dose effects. After inoculated, the value of LC50and LC90were shortened with inoculation time, at the7th day the larve’s LCsovalue is1.06×107conidia/mL and the value of LC90is6.95×109conidia/mL, the nymph’s LC50value is9.76×105conidia/mL and the value of LC90is8.17×108conidia/mL, the female adult’s LC50value is2.43×105conidia/mL and the value of LC90is1.01×108conidia/mL. The median lethal time of B. bassiana to T.cinnabarinus differed at various concentrations. Values of LT50of test were shortened with concentration. In the range of1.0×106～1.0×108conidia/mL, the LT50value of nymph decreased from6.94to3.99d, the LT50value of female adult decreased from5.80to3.90d. Furthermore, B. bassiana-treated can decrease fecundity, oviposition period and longevity of female adult dramatically, without affect hatchability and developmental duration of T.cinnabarinus. These results suggested the potential of isolate Bb025for use in microbial control of T.cinnabarinus.3. In our study, we evaluated the effect of B. bassiana-treated on A. cucμmeris’s fecundity and developmental duration. The result showed there is no significant difference between experimental group and control group. We also assessed effect of B. bassiana-treated on A.cucμmeris’s functional responses. Results indicated that functional responses of A. cucμmeris on both untreated and B. bassiana treated adults of T.cinnabarinus are Holling Type Ⅱ. Data analysis showed that handling time of predator was increased on treated T.cinnabarinus with the increase of the time after spray in comparison with that of untreated adults of T.cinnabarinus, respectively. Differences among treatments for handling time were significant. Attack rates, daily predatory amounts and searching efficiency were decrease to each others and there was significant difference in differenttime interval treatments. |
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