Abstract A nuclear polyhedrosis virus (SeNPV) was isolated from a single larva of the beet armyworm, Spodoptera exigua (Hubner), in Taiwan. Electron micrographs showed that the polydedra were irregular measuring ca. 1.05±0.21μm in diameter, and that the virion contained one to six nucleocapsids within the envelope. The virion is rodshaped, with parallel sides and round ends. The nucleocapsid is enlongated with parallel sides and straight end, measuring 48×285 nm. This SeNPV isolate is highly pathogenic to S. exigua larvae, its LC50 values are 1.6×105, 6.9×104, 4.1×104, 3.7×105, and 5.2×106 PIBs/ml for first to fifth instar, respectively, as assayed according to an inoculum-imbibing method. The LD50 values were estimated to be 4; 23; 57; 1,219; and 47,025 PIBs/larva for the respective instars, demonstrating that beet armyworm larvae become less susceptible to SeNOV wuth age. Histological sections showed that the nuclei of midgut, fat body, and epidermal cells were swollen after inoculation, followed by cell lysis and tissue disintegration.
摘要 自台灣埔里滿天星上甜菜夜蛾 (Spodoptera exigua) 病蟲體內分離之核多角體病毒，經穿透式電子顯微鏡觀察該病毒外形為不規則且大小不均一的多角體，平均直徑為1.05±0.21μm，在每一病毒粒子中含有一至六個長桿狀之核蛋白鞘，其中以包含2-4個為最常見。每個核蛋白鞘之大小平均約為285×48nm，兩端為平緩的圓弧形。由電子顯微鏡及組織病理切片之觀察可證實此病毒為甜菜夜蛾核多角體病毒 (SeNPV)。核多角體病毒對本省甜菜夜蛾幼蟲具有高度之致病力，以接種源飲入法測得一至五齡幼蟲之半致死濃度 (LC50) 依序為1.6×105，6.9×104，4.1×104，3.7×105及5.2×106 PIBs/ml，並推算其半致死劑量 (LD50) 分別為4、23、57、1,219及47,025 PIBs/la-rva，顯示隨著幼蟲齡期之增長，其對病毒之感受性亦明顯下降。而罹病幼蟲經以組織切片觀察，發現中腸細胞、脂肪體細胞及表皮細胞等細胞核均有明顯的腫大病變現象，病毒大量複製後導致細胞及組織崩解。
| Key words: Spodoptera exigua, nuclear polyhedrosis virus, SeNPV, pathogenicity, histopathology. | | 關鍵詞: 甜菜夜蛾、核多角體病毒、致病力、組織病理學。 |
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