| Tetranychus cinnabarinus (Boisduval) is a kind of important agricultural spider mites. It has become so difficult to control due to the strong reproductive ability, short generation time, very strong ability to adapt, insecticide resistance is on the rise for frequent use of chemical pesticide that more and more concentration has been draw to find new methods of biological control. The entomopathogenic fungus, Beauveria bassiana, is a fungal control agent which has been researched and applied for such a long time. It could be used to control plenty kinds of insect pests and has very good application potential and development prospects. Based on the previous study of our laboratory, the infection process of strain Bb025conidia on cuticle were observed using scanning electron microscope (SEM). The effects of temperature and humidity of Beauveria bassiana were tested. Six kinds of common acaricides used in fields were screened to evaluate compatibility between the fungus and the pesticides and fungal chemical interaction against spider mite Tetranychus cinnabarinus. The main results obtained are as follows:1. The infection process of Beauveria bassiana conidia on cuticle was observed using scanning electron microscope. The results showed that most of conidia deposited on the dorsal part of mite, ventri-anal plate, legs, trichodea, hair pores. The germinated conidia mainly invaded from depression part of mite surface and hair pores with sprout and hypha. We could observe penetrates atl2h after inoculation, hypha covered the whole mite12h after inoculation.2. In order to know the effect of temperature and humidity on the virulence of Beauveria bassiana strains Bb025against Tetranychus cinnabarinus. Five different temperature(19℃,22℃,25℃,28℃,31℃) and three levels of different humidity [(55±5)%RH,(75±5)%RH,(95±5)%RH] were set up in the test, and the female adults and eggs of Tetranychus cinnabarinus were infection with Bb025(1×108,2×107,4×106,8×105,1.6×105conidia/mL), then we recorded the mortality and hatching rate day by day. The results showed that the lethallty rates of treatments in25℃and28℃were significant higher than the treatments in the other temperatures.19℃is the most unfavorable temperature for Beauveria bassiana infection of Tetranychus cinnabarinus. The germination speed and rates of spores increased with the RH increasing, and high humidity could be in favour of the infection of Beauveria bassiana on Tetranychus cinnabarinus.3. The effects of6common acaricides, including pyridaben, fenpropathrin, hexythiazox, propargite, abamectin, dicofol on vegetative growth, conidia production, conidial germination of Beauveria bassiana strain BbO25were tested to explore the compatibility of chemical acaricides with Beauveria bassiana strain BbO25, and provide experimental evidence for combined chemical control and biological control application in fields. The results showed that there remained to be significant difference between vegetative growth, conidia production, and conidial germination under different acaricides with different concentration. The compatibility of abamectin and Beauveria bassiana was worst among all tested acaricides; the inhibition rates of vegetative growth, conidia production, and conidial germination at low concentration of abamectin were higher than60%. Fenpropathrin, dicofol, pyridaben played lightly auxo-action to vegetative growth at low concentration, and the inhibition rates of conidia production were significantly than other acaricides. The inhibition rates of conidial germination of these three acaricides were18.76%,14.50%, and8.31%, remained to be much lower than other three acaricides. Fenpropathrin, dicofol, pyridaben played lightly showed comparatively higher compatibility with Beauveria bassiana, providing good candidates of acaricides for mixed use with fungal insecticides.4. The lethal effect of interaction between Beauveria bassiana and low concentrations of pyridaben against Tetranychus cinnabarinus showed that the mortality rate increased with the increasing of conidia and concentration, and the time needed for death also significantly reduced, the interactions showed good synergistic effect. The eggs hatch had been obvious inhibition while treated with this combination. The lethallty rate was82.22%while the conidia concentration was1×10’ conidia/mL and the pyridaben concentration was2.5μg/mL which was significantly higher than simply treated with Beauveria bassiana conidia. The results indicated that there were also good synergistic effects of combination against with Tetranychus cinnabarinus eggs. |
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