Abstract: Beauveria bassiana HFW-05 strain is highly virulent against Bamisia tabaci． To broaden its insecticidal range and determine the joint toxicity of the mixtures of conidia spores and chemical pesticides， the bioassay ofHFW-05 strain to 2nd and 3 rd instar larvae of diamondback moth， Plutella xylostella( L． ) and the conidia germination and mycelia growth of HFW-05 were carried out． The results showed that HFW-05 strain was highly toxic to larvae of diamondback moth． The corrected motality of conidia spores of the concentration 5 107 /mL to 2nd and 3 rd instar larvae 6 d after infection were 86． 7% and 76． 7% separately， and the toxicity to the 2nd instar larvae wasmarkerdly higher than to 3 rd instar larvae at all tested concentration． The inhibitory action of chemical agents onspores was significantly reduced with decreasing concentration． There was no significant correlation between the impact of chemicals on spores and the toxicity of fungus mixed drug to P．xylostella． At conventional dosage， chlorfluazuron， cyhalothrin and phoxim strongly inhibited spores growth with 0， 0 and 7． 9% germination respectively． Thevirulence of 5-fold dilution of phoxim， methomyl and diflubenzuron Ⅲ mixed 1 × 106 /mL spores to the P．xylostellaexhibited antergic with corrected mortality 23 ． 4% ， 16． 2% and 20． 5% respectively． But the other agents showed additive effect for the toxicity to P．xylostella． Chlorfluazuron and fipronil showed significant synergistic activity withcorrected mortality 93． 3% and 98． 0% separately． This result may be used to improve biocontrol of the pest．

Key words: Beauveria bassiana, Plutella xylostella ( L． ) , Chemical pesticide, Joint toxicity, Synergistic activity

CLC Number: 

• S476.1