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为了阐明斜纹夜蛾Spodoptera litura Fabricius幼虫密度对其抗病能力的影响,在室内条件下(温度23℃±1℃,相对湿度75%)对不同幼虫密度(1、2、5、10、15头/皿(直径为12cm))饲养的斜纹夜蛾幼虫抵抗斜纹夜蛾核型多角体病毒侵染的能力及其免疫指标进行了研究。结果表明:幼虫密度对斜纹夜蛾幼虫接种核型多角体病毒后的存活率、存活时间及血淋巴酚氧化酶活性影响显著。随着幼虫密度的增加,接种核型多角体病毒后幼虫的存活率降低,存活时间缩短。当幼虫密度达到15头/皿时,幼虫存活率显著低于其它幼虫密度。不同幼虫密度幼虫的存活时间以1头/皿的最高,15头/皿的最低,且二者之间差异显著。幼虫血淋巴中酚氧化酶活性随幼虫密度的增加而明显降低,当幼虫密度达到5头/皿时,幼虫酚氧化酶活性显著低于1头/皿的。另外,幼虫溶菌酶活性和血细胞总数受幼虫密度影响不显著。不同密度幼虫抗病性的变化与其血淋巴中酚氧化酶活性的变化趋势较为一致。所以斜纹夜蛾幼虫抗病能力的降低可能与幼虫酚氧化酶活性的下降有关。因此,幼虫密度是影响斜纹夜蛾幼虫抗病性变化的重要因子。
In order to elucidate the effects of density of Spodoptera litura Fabricius on the disease resistance of Spodoptera litura, the density of larvae (1, 2, 5, 10, 15 heads) (Diameter of 12cm)) were fed on the infecting ability of Spodoptera litura nucleopolyhedrovirus and its immune parameters were studied. The results showed that the larval density significantly affected the survival rate, survival time and hemolymph phenoloxidase activity of Spodoptera litura larvae after inoculation of nuclear polyhedrosis virus. With the increase of larval density, larvae survival rate decreased and survival time shortened after inoculation of nuclear polyhedrosis virus. When the larvae density reached 15 heads / dish, larvae survival was significantly lower than other larval density. The larval density of different larvae survival time of 1 head / dish the highest, 15 heads / dish of the lowest, and the difference between the two significant. The larvae hemolymph phenoloxidase activity decreased significantly with the increase of larval density, larvae density reached 5 head / dish, larval phenoloxidase activity was significantly lower than 1 / plate. In addition, larval lysozyme activity and total number of blood cells affected by larval density was not significant. The change of disease resistance of larvae with different density and the change tendency of the activity of phenoloxidase in hemolymph were consistent. Therefore, the reduced resistance of S. litura larvae may be related to the decline of larval phenoloxidase activity. Therefore, larval density is an important factor that affects the variation of resistance of S. litura larvae.