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|標題:||Host Infection, Persistence in Soil and Field Application of the Entomopathogenic Nematode, Steinernema abbasi|
field control efficacy
|摘要:||在實驗室內，探討蟲生線蟲(Steinernema abbasi)感染寄主之生物特性及土壤對其持效力之影響；在田間試驗中，評估該線蟲對斜紋夜蛾(Spodoptera litura)及亞洲玉米螟(Ostrinia furnacalis)的殺蟲效力。寄主對感染期線蟲(infective juveniles; IJs)具明顯的誘引效果，並可提昇其垂直分散能力。在砂壤土及砂土中，S. abbasi之理想殺蟲效力分別達10 cm及15 cm深；當寄主同時存在於不同土壤深度時，該線蟲的理想殺蟲效力縮小至10 cm。S. abbasi可經由大蠟蛾(Galleria mellonella)幼蟲體壁、節間膜、腹足等處直接侵入寄主體內。在26℃下，S. abbasi在大蠟蛾幼蟲體內完成生活史需時約4日，離開寄主的齡期為J3；J3經2-3日後，發育為IJs。在20℃下，該線蟲雖可感染寄主，但無法完成其生活史。利用大蠟蛾蟲體繁殖S. abbasi時，線蟲的適當接種量為500 2,000 IJs/larva，線蟲產量達1.8 105 IJs/larva。S. abbasi接種100 IJs對斜紋夜蛾、玉米穗夜蛾(Helicoverpa armigera)、小菜蛾(Plutella xylostella)、黑角舞蛾(Lymantria xylina)等十六種鱗翅目昆蟲具適當的殺蟲效力，幼蟲死亡率在86.7 100 %之間，但對蜚蠊目、直翅目、鞘翅目及雙翅目等昆蟲的感染力則較不理想。斜紋夜蛾幼蟲對線蟲的感受力程度為：五齡蟲>四齡蟲>末齡蟲>前蛹
期幼蟲>三齡蟲。S. abbasi在砂土或砂壤土中具理想的持效力，但在壤土及黏土中的持效力則隨時間延長而遞減。在20 35℃下，S. abbasi可維持適當的持效力至32日止。在2 16 %土壤含水量下，S. abbasi均可表現適當的持效力至16日或32日止。在土壤pH 4 8下，S. abbasi可維持適當的持效力。土壤含未腐熟有機肥時，S. abbasi的持效力會明顯降低；土壤含0.5 2.0 %之牛糞、豬糞及雞糞等腐熟有機肥時，該線蟲得以維持適當的持效力至32日止。土壤含1、5、39及43號 (台灣肥料公司)等四種化學肥時，S. abbasi之殺蟲效力會受到嚴重的負面影響。S. abbasi與歐滅松(omethoate)、芬化利(fenvalerate)、百滅寧(permethrin)、畢芬寧(bifenthrin)、歐殺松(acephate)及賽滅淨(cyromazine)等六種殺蟲劑具相容性，且該六種藥劑對線蟲在土壤之持效力影響不顯著。在蔬菜區土壤樣品中，線蟲得以有效殺死大蠟蛾幼蟲之樣品比率僅50 %。在模擬田間試驗中，將5.0 105 IJs/m2施於表土後，對斜紋夜蛾末齡蟲的防治率達76.8 86.3 %。當幼蟲密度 8 larvae/plot時，線蟲施用後，可有效保護葉面被害程度。晚春及夏季時，蕹菜採收前7 10日施用線蟲，可獲顯著的田間殺蟲效力。在田間試驗中，於溫度22.0 25.0℃，90 96 % RH時，葉面施用1.0 106 IJs/m2後，經12 hr，線蟲存活數仍達10 IJs/cm2以上，且對斜紋夜蛾三齡蟲的防治率高達82.7 %。土壤或葉面溫度低於20℃時，不利線蟲感染力之表現。玉米施用40,000 IJs/ear後，線蟲在玉米穗端部及玉米穗中、基部對亞洲玉米螟之殺蟲效力分別為81.1及16.8 %。施用4,000 IJs/ear (一次)、4,000 IJs/ear (兩次)及carbofuran後，玉米被害粒數皆低於對照組；且三處理組中符合可上市玉米穗率相當高。本試驗結果顯示S. abbasi對斜紋夜蛾及亞洲玉米螟幼蟲具理想的殺蟲效力，對玉米品質的保護效果相當顯著，推薦該線蟲為防治該二種害蟲之安全有效的蟲生病原。|
In the laboratory, studies were conducted on biological characterization of host infection with Steinernema abbasi, and persistence of the nematode in soil. In field trials, studies were conducted on field efficacy of the nematode against Spodoptera litura and Ostrinia furnacalis. The vertical distribution of infective juveniles (IJs) might be enhanced when their hosts emerged in soil. In sandy loam and sand, S. abbasi could reach 10 and 15 cm depth of soil with high infectivity, respectively; nevertheless, this nematode just could reach 10 cm depth of soil when the hosts were distributed evenly at different depths of soil. S. abbasi penetrated through the integument, intersegmental membrane, and abdominal legs, and then entered the body cavity of Galleria mellonella larvae. S. abbasi completed its life cycle in G. mellonella larva about 4 days at 26℃, and the developmental stage emerged from hosts was J3. Then J3 developed to IJs within 2 3 days. However, the nematodes could not complete their life cycle in hosts at 20℃. In vivo culture, the optimum inoculum size of S. abbasi was between 500 2,000 IJs/larva in G. mellonella larvae, and the yield of progeny nematode could reach 1.8 105 IJs/larva. S. abbasi at 100 IJs showed a high infectivity to 16 species of Lepidoptera, for example, S. litura, Helicoverpa armigera, Plutella xylostella, and Lymantria xylina, resulting in 86.7 100 % mortality. The level of larval susceptibility to the nematode was in order of 5th instar > 4th instar > 6th instar > prepuape > 3rd instar. However, the nematode was less infective to the species of Blattodea, Orthoptera, Coleoptera, and Diptera. Sand and sandy loam were more suitable for S. abbasi persistence; but in loam and clay, the persistence of the nematode was decreased as the time prolonged. S. abbasi could be persistent until 32 days at 20 35℃. S. abbasi could be persistent until 16 days or 32 days at 2 16 % soil moisture. the nematode showed optimum persistence under soil pH 4 6, but in alkali soil, persistence of the nematode was declined. In the soil containing undecomposed organic fertilizers, persistence of the nematode was low; in the soil containing 0.5 2.0 % decomposed organic fertilizer made of cattle feces, pig feces, or chicken feces, the nematode remained persistence until 32 days. However, in the soil containing no. 1, 5, 39, and 43 (Taimwan Fertilizer CO., Ltd.) chemical fertilizers, persistence of the nematode was severely hampered. S. abbasi was compatible with insecticides, e.g., omethoate, fenvalerate, permethrin, bifenthrin, acephate, and cyromazine, in terms of persistence in soil. In soil samples collected from various vegetable cultivars, only 50 % samples rendered the nematode to effectively infect the larvae of G. mellonella or to keep appropriate persistence. In simulated field trials, the control rate of nematode against the last instar larvae was 76.8 86.3 % when a nematode concentration of 5.0 105 IJs/m2 was applied onto the soil surface. The foliage injury level was effectively reduced after inoculated with less than 8 larvae/plot. In late spring and summer seasons, field efficacy was more remarkable when the nematode was applied during 7 10 days before harvesting in water celery. In field trials, when the leaves were sprayed with 1.0 106 IJs/m2 under 22.0 25.0℃ , 90 96 % RH, the nematode survival was found to be over 10 IJs/cm2 at 12 hr after spraying, and the control rate of nematode against the 3rd instar larvae was 82.7 %. Nevertheless, S. abbasi was less infective to the host under the soil or foliar temperature below 20℃. The larval mortality of Ostrinia furnacalis on the ear end and the middle or bottom of ear was 81.1 and 16.8 %, respectively, after applying 40,000 IJs/ear. The numbers of kernels injured after applying 4,000 IJs/ear (once), 4,000 IJs/ear (twice), and carbofuran were all less than the control, and the marketable corns among treatments were not significantly different. These experiments revealed effectiveness of applying S. abbasi against S. litura or O. furnacalis, and provide an effective and safe strategy of pest management in controlling these pests.
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