[Screening for virulence strains of Metarhizium against Dorysthenes hydropicus pascoes].

OBJECTIVE: The aim of the present study was to screen the Metarhizium strains with high virulence against the larvae of Dorysthenes hydropicus, a serious pest of Citrus grandis. METHOD: Thirty six strains of Metarhiziums were isolated from the soil of C. grandis GAP base and collected from other institutions, and the pathogenicity of these strains against 1st instar larvae of D. hydropicus was detected at concentration of 1 x 10(8) conidia/g. The high violence strains against D. hydropicus were cultivated in sabouraud dextrose yeast medium at first, then transfer to rice grain. And the sporulations of these violent strains against D. hydropicus were detected. RESULT: Twenty-eight strains showed virulence against D. hydropicus by preliminary study, and 7 strains of them were collected for further study, 6 of the 7 showed high virulence, the highest cadaver rate was higher than 74%. The conidia production of strain 1 and strain 4 were 2.35 +/- 0. 25 (1 x 10(9) conidia/g), 2.21 +/- 0.27 (1 x 10(9) conidia/g), respectively, showed significantly higher than other strains. CONCLUSION: Strain 1 and strain 4 of the 36 Metarhiziums strains showed high virulence against D. hydropicus, and the highest sporulation ability, so they have a best application prospect.

[Primary studies on biological characteristics of Dorysthenes hydropicus].

OBJECTIVE: To study the biological characteristics of Dorysthenes hydropicus in the farm of Cirtus grandis, and offer scientific evidence for prevention and controlling of D. hydropicus. METHOD: Indoor-rearing and light trap were applied to study the biological characteristics, development course and harmful effect of D. hydropicus. RESULT: D. hydropicus reproduces one generation in 1-2 year in Guangdong province, and overwinters in the form of larvae. Its imago comes out of the earth mainly in late May after mature. The body length has great individual diversity normally ranged from 25-60 cm, It also shows strong phototaxy. One lamp can trap more than 2 000 of them per night. Female imago has a large egg load with the maximum amount of 543. The eggs hatching is in depth of 1-3 cm soil. The dominant hatching period of egg is from late June to early July, and hatchability is over 85%. The living space of larva ranges from 15-60 cm in soil. D. hydropicus has caused serious harm and lead to thousands of Cirtus grandis trees death every year. CONCLUSION: Dorysthenes hydropicus showed serious threat to the growth of Cirtus grandis and should be prevented and controlled.