蟲生線蟲感染斜紋夜蛾之研究

本試驗研究蟲生線蟲，Steinernema carpocapsae All strain ，在室內 感染斜紋蛾，Spodoptera litura，探討以活體培養之蟲生線蟲與體外培 養者間感染斜紋夜蛾之效力及其對農藥之忍受性。 以S. carpocapsae感 染斜紋夜蛾末齡幼蟲，使其成功化蛹後，形成自然的包囊體，可將之施用 於土壤表層，感染斜紋夜蛾幼蟲。為利於人工飼料培養線蟲，將共生細菌 用Nutrient broth 培養液培養，再採MacConkey''s agar 與 NBTA 二種培 養基，分別作平板劃菌培養，未經體外培養與分別培養於體外經７２小時 之共生細菌間，其呈色反應皆無明顯差異，應為第一型共生細菌。選取六 種培養基質，作為蟲生線蟲培養之用，其中未先行培養共生細菌之處理者 ，幾乎都未有線蟲離開其培養基，但可持續存活且活動良好。而先接種共 生細菌培養４８小時後，再接種蟲生線蟲作培養者，可產生IJ的數量，以 黃豆粉添加定量膽固醇培養基之產量最高，在１５天收成期內，平均每克 培養基可生產8.14＊10^4IJs，且豬腦培養基與黃豆粉添加定量膽固醇之 培養基於接種線蟲培養後第17天皆達其產量高峰。以豬腦及黃豆粉結合動 物性和植物性成份配製之培養基，以不同比例混合供生產IJ，其中以1:1 之混合比所配製的培養基，待接種共生菌培養48小時後，再接種線蟲， 於15天收成期內，平均每克培養基可產6.83*10^4IJs為最佳。活體與人工 飼料培養之IJ對於三及五齡幼蟲之半數致死濃度(LC50)相近，而對於各齡 幼蟲之半數致死時間(LT50)，則以人工飼料培養之IJ較活體培養者為長。 活體與人工飼料培養之IJ對於殺蟲劑和殺草劑之忍受性均較殺線蟲劑為小 ，而且以上二種方式所生產之IJ經各類藥劑處理後，皆有蜷曲的現象。以 IJ感染斜紋夜蛾臨化蛹前24小時內之末齡幼蟲，經72小時，以20IJs/0.1 ml處理者平均每克蛹體可產3.97*10^4IJs為最佳。自蛹體產生的可經蛹體 之氣孔及節間膜釋出；將受感染之蛹體置於25℃下8天後，移至含水 量9.09％，厚2cm之土層上方，於72小時後，自該蛹體釋出之IJ感染斜紋 夜蛾五齡幼蟲所造成之死亡率高達95％。但受感染之蛹體經冷藏於1℃下 經過3?及7天後，其感染幼蟲所造成之死亡率，隨冷藏時間增加而降低； 在斜紋夜蛾五齡幼蟲體內培養IJ於培養後第9天可達產量高峰，平均每克 蟲體可產生1.96*10^5IJs與其它培養方式之產量有極顯著的差異。Infection of the common cutworm, Spodoptera litura, with the entomopathogenic nematode,Steinernema carpocapsae All strain, was studies under laboratory conditions. Theinfectivity of S. carpocapsae cultured in vivo and in vitro to S. litura and itstolerance to pesticides were investigated in thes study. The last instar larvae of S. litura infected with infective juvenile (IJ) could pupate successfully and formed the nematode- containing natural capsules. The capsule is ready to apply to soik surface for infecting S.litura alrvae. Symbiotic bacteria of S. carpocapsae were isolated and cultured in nutrient broth and were found to be beneficial to the nematode culture in vitro.Identification of phase variants of the symiotic bacteria by MacConkey''s agar plate and NBTA plate revealed that all of them were primary form during 72hr culture.The artificial media for nematode culture were prepared with six selected basic substances.There were almost no IJs liberating from the media without inoculating symbioticbacteria before adding nematode suspension, but most of the nematodes were viable in media. The IJ production was best in the media mixed soy flour with cholestrol and inoculated symbiotic baceria before adding nematode suspension, 8.14*10^4 IJs/g being harvested during culturing for 15 days. The IJ production by both pig brainmedium and soy flour medium with cholestrol had a peak at day 17 after culture. The media mixed soy flour with pig brain by different ratios were also prepared for nematode culture. The best IJ production was found by the medium with the ratio of 1to 1, 6.83*10^4 IJs/g being harvested during culturing for 15 days.The LC50 values of of IJ cultured in vivo and in vitro for 3rd and 5th instar larvae were similar, butthe LT50 caused by IJ Cultured in vitro was longer. Tolerance of IJ cultured in vivo and in vitroto insecticides and herbicides were both lower than to nematicides. The IJs treated with various pesticides became pretzeltwist shape. The prepupae within 24 hr were infceted with 20IJs/0.1ml suspension, resulting in 84.6% pupation. The best production of IJs cultured in pupae was 3.97*10^4IJs/g, being able to leave host through spiracles or cuticular membrane. The nematode-containing pupae were stored at 25℃, 8 days, and then were placed onto the soil surface containing 9.09% water (W/W) for testing infectivity to 5th instar larvae of S. litura. The larval mrotality in soil was 95% after incubating for 72 hr. However the mortality declined after preserving at 1℃ for 3、5 and 7 days.The IJ production by culturing in 5th instar larvae had a peak at day 9 after culture, about 1.96*10^5 IJs/g being harvested. This is significantly different from that produced in other cultures