斜紋夜蛾(Spodoptera litura)在甘藍、芋頭及田菁上的族群介量與取食量

Abstract

斜紋夜蛾(Spodoptera litura (Fabricius))為廣食性害蟲，可危害多種作物，研究其在不同作物上之生活史特徵、兩性生命表及取食量可對於其族群生態及在不同作物上的族群成長潛能有更廣泛的了解。本試驗於定溫25 ± 1ºC及相對濕度60 ± 10%的環境下，研究斜紋夜蛾在甘藍、芋頭及田菁三種不同作物上之取食量及生長繁殖，並分析三種作物在水、蛋白質、氮及非結構性碳水化合物之含量。營養分析結果顯示，甘藍除了含水量最高外，其他營養成分皆為最低。然而，幼蟲期取食量以取食甘藍者為最高，淨取食率為439.1 cm2，為取食田菁207.8 cm2及芋頭的141.7 cm2的2~3倍之多。因此，推測斜紋夜蛾幼蟲藉由補償取食作用使各齡期頭殼寬及體重皆以取食甘藍者為最佳。兩性生命表分析結果顯示，在甘藍上之淨增殖率(R0)、內在增殖率(r)及終極增殖率(λ)均為最高，分別為1893.1 offspring、0.2374 d-1及1.2679 d-1；田菁次之，分別為1420.1 offspring、0.2331 d-1及1.2624 d-1；而在芋頭上為最低，分別為1361.0 offspring、0.2298 d-1及1.2584 d-1；平均世代時間(T)則以甘藍上31.8 d為最長，田菁上之31.2 d為最短，具有顯著差異。結果顯示，斜紋夜蛾具有適應不同作物中不同營養含量及營養比例的能力。甘藍、芋頭以及田菁皆適合斜紋夜蛾之生長繁殖，其中又以甘藍最為適合。田菁為台灣重要的夏季綠肥之一，本試驗證實斜紋夜蛾在田菁上的生長繁殖潛能相當好。因田菁被廣為種植作為綠肥作物，以及斜紋夜蛾成蟲具有很強的遷飛能力，故針對田菁田擬定斜紋夜蛾的害蟲管理計畫是必要的。否則可能使田菁成為斜紋夜蛾之替代作物，進而遷飛到鄰近經濟作物或雜草上危害，增加斜紋夜蛾害蟲管理的困難。

Spodoptera litura (Fabricius) is a polyphagous insect that can damage numerous hosts. Investigations of their life history traits, life table, and food consumption can offer a comprehensive understanding of the population growth potential of S. litura on different plant species. In this study, the performance of S. litura reared on cabbage, taro, and sesbania was investigated in a walk-in growth chamber at 25 � 1ºC, 60 � 10% RH, and a photoperiod of 12:12 (L:D). The water, protein, nitrogen, and non-structural carbohydrate contents of these three hosts were analyzed. The nutrient analysis revealed that the protein, nitrogen, and total non-structural carbohydrate contents were much lower on cabbage, though the water content was not. However, the net consumption rate on cabbage was 439.1 cm2 and was 2 to 3 times higher than that for those fed on sesbania (207.8 cm2) and taro (141.7 cm2). Therefore, it might be due to the compensation effect that the results showed the largest head capsule width and heaviest body weight of larvae when the insects were reared on cabbage. The results of the age-stage, two-sex life table showed that the population parameters of net reproductive rate, intrinsic rate of increase, and finite rate of increase were all significantly highest on cabbage (1893.1 offsprings, 0.2374 d-1, 1.2679 d-1), followed by sesbania (1420.1 offspring, 0.2331 d-1, 1.2624 d-1), and lowest on taro (1361.0 offsprings, 0.2298 d-1, 1.2584 d-1). The mean generation time was the shortest on sesbania (31.2 d) and the longest on cabbage (31.8 d). S. litura showed the ability to adapt to varied nutrient contents in different hosts. Cabbage, taro, and sesbania were all suitable hosts for S. litura, but they performed the best on cabbage. S. litura also showed a high population potential on sesbania, which is a major green manure crop in the summer in Taiwan. Because sesbania is widely planted and S. litura can migrate long distances, an efficient pest management program aimed at S. litura in sesbania fields is necessary; otherwise, S. litura can build their population on sesbania and then migrate to adjacent economic crops or weeds, and increase the difficulty in pest management.