Abstract Third-instar Spodoptera litura larvae were infected with various combinations of polyhedral inclusion bodies (PIBs) of S. litura nucleopolyhedrovirus (SpltNPV) and spores of a microsporidium, Nosema spodopterae, by the diet surface contamination method. LD50 values of SpltNPV and N. spodopterae to third-instar larvae of S. litura 21 days post-infection (incubated at 26 ± 2°C, 75–80% RH, and L:D = 12:12) were 8.51 × 103 PIBs/larva and 1.13 × 104 spores/larva, respectively. The numbers of dead larvae after coinfections with the two pathogens were counted, and two lethal peaks were found at 8 and 18 days post-infection. The dead larvae first contained PIBs only and later contained spores only. These two lethal times coincided with those of infection with SpltNPV only or N. spodopterae only, respectively. Only 0.5% of dead larvae contained both PIBs and spores. The results of binomial tests of accumulated mortalities reveal that antagonism between the two pathogens occurred at combinations of 5 × 103 spores with PIBs, and independence occurred especially at high spore dosages. The factor of interference existing with coinfection of SpltNPV and N. spodopterae needs to be elucidated in future studies.
摘要 以斜紋夜蛾 (Spodoptera litura) 之兩種重要病原體──斜紋夜蛾核多角體病毒 (S. litura nucleopolyhedrovirus, SpltNPV) 與斜紋夜蛾微孢子蟲 (Nosema spodopterae)──混合感染斜紋夜蛾三齡幼蟲。於26 °C下，接種後21日之兩種病原體單獨感染之LD50值各為SpltNPV: 8.51×103 PIBs/larva、N. spodopterae: 1.13 × 104 spores/larva。混合感染試驗結果顯示因核多角體病死亡之高峰期在接種後第8日，而因微孢子蟲病死亡之高峰期則於第18日。在鏡檢下，死亡幼蟲中只有0.5%可檢測到病毒包涵體與微孢子蟲孢子，其餘則只檢測出單一病原體 (SpltNPV或N. spodopterae)。利用累積死亡率進行二項分佈檢定 (binomial test)，發現只有在N. spodopterae 劑量為5×103 spores/larva時對不同核多角體病毒劑量呈拮抗作用 (antagonism)，高劑量的微孢子蟲則與核多角體病毒之感染呈不相關 (independence) 的現象，Tammes圖形分析結果亦相似。但高劑量的微孢子蟲感染會抑制核多角體病的發生，因此，此二種病原體間在同一寄主內確實的干擾因子有待進一步釐清。
| Key words: antagonism, coinfection, Nosema spodopterae, Spodoptera litura nucleopolyhedrovirus (SpltNPV). | | 關鍵詞: 斜紋夜蛾核多角體病毒、斜紋夜蛾微孢子蟲、共感染、拮抗作用 |
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