| Summary: | 碩士 === 國立臺灣大學 === 昆蟲學研究所 === 89 === Perina nuda Fabricius is a major pest of banyan（Ficus spp.）, an important tree in gardens and forests throughout Taiwan. The epizootic diseases, nucleopolyhedrosis and flacherie, were found in the natural population of this insect. Our aim was to study these two caused agents, PenuNPV（P. nuda nucleopolyhedrovirus） and PnPV（P. nuda picorna-like virus）. This study included （1）establishment of a rearing method in the laboratory; （2）nature infectivity of PenuNPV in P. nuda population; （3）the PenuNPV susceptibility of P. nuda larvae（LD50）;（4）co-infection of PenuNPV and PnPV to P. nuda larvae; and（5）organ or tissue infectivity of PnPV. Perina nuda can grow and develop throughout the year in Taiwan. The fresh leaf of F. microcarpa L. f Golden Leaves. is highly suitable for rearing larvae in the laboratory. In nature, the PenuNPV-infection rate of the larvae is correlated positively with the density of the P. nuda population. The peak PenuNPV-infection rate（70.27%） and population density each occurred in May. The susceptibility of P. nuda larvae to PenuNPV declined with larval stage. LD50 of PenuNVP to the 2nd-instar larvae was 1000 times that of the 5th-instar larvae. A co-infection study of PnPV with PenuNPV showed that the synergistic effect occurs not only at the low-dose-PenuNPV infection, but also at the high-dose-PenuNPV infection. The organs or tissues derived from the 6th-instar larvae, infected previously with PnPV at their 2nd-instar stage, were determined with RT-PCR to have PnPV infection. Results showed that muscle, nerve, midgut, fat body（green in color）, reproductive gland and silk gland were all positive, with midgut and muscle showing especially strong reactions. In conclusion, we confirmed that the seasonal epizootics of P. nuda is nucleopolyhedrosis, while PnPV caused only a latent infection. The synergistic effect of PnPV with PenuNPV only occurred at low-dose-PenuNPV infections.
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