| Abstract: | Abstract The entomophthoralean fungus, Pandwa delphacis (Hori) Humber, is a pathogen frequently causing epizootics of the brown planthopper, Nilaparvata lugens Stal, in rice growing areas of China. Two isolates (F95127 and F95129) of the fungus obtained from mycosis-killed planthoppers collected in Zhejiang Province were bioassayed for their virulence to N. lugens. For inoculation, botches of 4– or 5-in-star-old nymphs from a laboratory population were exposed to time-varying spore shower from sporulating plates of fungal mass produced in Sabouraud liquid medium, resulting in 8 and 6 dosages for F95129 and F95127, respectively. The nymphs treated at each dosage were maintained on rice plants at 25°C and a photophase of 12L: 12D in growth chamber (nearly 100% RH) and were examined daily for mortality. The resulting data were well fitted to time-dose-mortality model, generating parameters of time and dose effects for estimation of virulence indices. The LD50 values 6–8 d after exposure were 327, 122 and 46 conidia/mm2 for F95129 and 409, 133 and 74 conidia/mm2 for F95127, respectively. The LT50 estimated for F95127 was 7. 6 d at 95 conidia/mm2 whereas that for F95129 decreased from 6. 6 d at 172 conidia/mm2 to 5. 6 d at 525 conidia/mm2. Based on these virulence indices and comparison of the slopes for dose effects from the model, the two isolates of P. delphacis had moderate virulence to N. lugens with insignificant difference to each other. |
