兩種蟲生線蟲Steinernema abbasi及Steinernema carpocapsae對黑角舞蛾(鱗翅目：毒蛾科)致病力之比較

Abstract

Pathogenicity of two entomopathogenic nematodes, Steinernema abbasi and S. carpocapsae, and their potential applications in the field against the casuarina tussock moth, Lymantria xylina, were conducted in this study. Inoculation with different concentrations of S. abbasi and S. carpocapsae to 3rd- 6th instar larvae of L. xylina, the LT50 values treated with S. carpocapsae were shorter than those with S. abbasi in all larval instars. The LT50 values of 6th instar larvae infected with S. abbasi and S. carpocapsae at 20 IJs/larva were 89.8 h and 67.4 h, while the LT50 values of 3th instar larvae infected with S. abbasi and S. carpocapsae at 15 IJs/larva were 40.5 h and 24.7 h, respectively. The effect of temperature on pathogenicity of S. abbasi and S. carpocapsae to L. xylina was tested by inoculating 4th instar larvae with 20 IJs/larva at 20℃, 25℃, and 30℃. The LT50 values infected with S. abbasi at 20℃, 25℃, and 30℃ were 64.3, 43.9, and 30.7 h, whereas those with S. carpocapsae were 32.3, 25.2, and 16.4 h, respectively. These results showed that the LT50 values were decreased while increasing the treating temperatures in both nematodes. Inoculation of 4th instar larvae of L. xylina with S. abbasi and S. carpocapsae at 20 IJs/larva in artificial simulated seasons, i.e., spring and fall (L：D = 12：12 h；26：22℃), summer (L：D = 13 h 20 min：10 h 40 min；31：27℃), and winter (L：D = 11：13 h；21：16℃). The LT50 values infected with S. abbasi at 20 IJs/larva under spring, fall and winter were 35.4, 35.2, and 56.3 h, respectively, while those with S. carpocapsae were 30.4, 26.6, and 36.2 h, respectively. Therefore, the pathogenicity of both nematodes in winter was lower than that in other seasons. While inoculating 4th instar larvae with S. abbasi and S. carpocapsae at 100 and 300 IJs/L in greenhouse, the LT50 values of 4th instar larvae incubated at night were shorter than those in daytime as treated with both nematodes at the same concentration. In small scale field experiments treating with 1x105, 3x105 IJs/L, the mortalities of L. xylina larvae was not significantly different between both nematodes, resulting in only 22.7% - 42.4%, while the larval mortality was reached 87.2% as treated with fenvalerate. Therefore, it is suggested that effective application techniques of these two entomopathogenic nematodes in the field have to be further developed.