| Beauveria bassiana (Balsamo) Vuillemin is one of the entomopathogenic fungi which applied the most twidely presently at home and abroad, to pest control effeetively.I tcould infect more than 700 Species insects of 149 Families in 15 Orders, and caused the epidemicdis of pest, lasted control. A more virulent strain, HFW-05, to nymph of B. tabaci and P. xylostella was obtained by Laboratory of Microbial insecticide Institute of Plant Protection, Hebei Agricultural and Forestry Science. In this paper, the expansion of insecticidal spectrum of the HFW-05 strain, and infection of Bemisia tabaci and Plutella xylostella would be studied. The thermotolerance of the strain could be improved by high temperature stress, and got a new more stable strain.The HFW-05 strain has virulence against B. tabaci, P. xylostella, Helicoverpa armigera, Locusta migratoria manilensis, Holotrichia oblira, Holotrichia parallela and Anomala corpulenta was showed by the bioassay. All of those pest could be infected through the skin, except Helicoverpa armigera. The formulation brought on high mortality of two tested Pest in the lab and field. HFW-05 strain was toxic to the 3rd larvae of Bemisia tabaci with an LC50 of 4.20×105conidia/mL, to the 2rd of Plutella xylostella with an LC50 of 1.59×106 conidia/mL, and the mortality could be 80% in the field. The action time to the other pests would be longer .The mortality of HFW-05 with 107 conidia/mL to locusta migratoria manilensis after 9 days and to Holotrichia oblira, Holotrichia parallela and Anomala corpulenta after 12 days could be 62.67%, 60%, 46% and 40.74%. Stomach infection had be found on Helicoverpa armigera, Weight and food consumption bad be inhibited obviously.The paraffin slice of and Helicoverpa armigera infected by HFW-05 showed that the conidia infected Bemisia tabaci through the skin, hypha first penetrated the abdomen,and firstly pierced surface from the abdomen . Skin infection was not found on Helicoverpa armigera, conidias were found in digestive tract,germination and growth was showed ,and tissues was full of hypha when the pest was dead. Skin infection on Helicoverpa armigera by B. bassiana had been reported mostly. Further explanation of the phenomenon is the infection to the host by Beauveria bassiana is different for differernt insect species, instars and environmental conditions.HFW-05 strain was domesticated directionaly with high temperature stress for improving the thermotolerance. Conidia suspension were exposed to a thermal stress of water bath under 48°C for 30, 40, 50, 60, 70, 80, 90, 100, 110, 120min, then mensurated the residue viabilities of conidia, rate of growth, sporulation, hydrophobicity virulence, extracellular protease and chitinase. The treatment which have high heat resistance after thermal stress were teratde with the same approach to the 8th generation.The results showed that thermotolerance of the strain which were exposed to a thermal stress of under 48°C water bath for 60 and 110 min to the 8th generation have been obviously improved.The heat-resistant and control strains were subcultured at the same time at 30℃. After 5 generation, the germination rate of the control strain was 15%,but the heat-resistant strains, were 50%, the Virulence against Plutella xylostella by the control was too little ,but the heat-resistant strains, were more than 50% at 30℃and more than 30% at 32℃. This study shows that the appropriate heat treatment can greatly improve the heat resistance of Beauveria bassiana,it provided a scientific basis for solving the problem that the high-temperature environment limitations Beauveria bassiana faced when applicated in the field.
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