兩種蟲生線蟲Steinernema abbasi及S. carpocapsae對小白紋毒蛾（鱗翅目：毒蛾科）致病力之比較

Abstract

Entomopathogenic nematodes (EPNs) have been regarded as potential biological control agents against insect pests. In this study, two EPNs, Steinernema abbasi and Steinernema carpocapsae, were assayed to determine their pathogenicity against the small tussock moth, Orgyia postica (Walker) in the laboratory. When inoculated with different concentrations of nematodes to 2nd-5th instar larvae of O. postica, the LT50 values treated with S. carpocapsae were shorter than those with S. abbasi in most instars tested except the 5th instar. The cumulative mortalities of 2nd instar larvae treated with S. abbasi were 50-74.1%, while those of others were 78.3-100%. The LT50 values of S. abbasi against 4th instar larvae inoculated with 20 IJs/0.5 ml/larva at 20, 25, 30 and 35°C were 61.2, 42.8, 29.9 and 21.6 h, respectively, while those of S. carpocapsae were 50.6, 25.1, 21.5 and 18.3 h, respectively. These results showed that the LT50 values declined as elevated the incubating temperatures inoculated with both nematodes. Inoculations of 4th instar larvae of O. postica with S. abbasi and S. carpocapsae at 20 and 30 IJs/0.5 ml/larva were conducted in artificial simulated seasons where summer was L : D = 13 h 20 min : 10 h 40 min ; 31 : 27°C and winter L : D = 13 : 11 h ; 21 : 16°C. The LT50 values infected with S. abbasi at 20 and 30 IJs/0.5 ml/larva under summer were 43.1 and 38.8 h, respectively, but the cumulative mortality under winter was only 20-26.7%. The LT50 values infected with S. carpocapsae at 20 and 30 IJs/0.5 ml/larva under summer were 37.9 and 36.2 h, respectively, whereas those under winter were 53.5 and 57.1 h, respectively. The pathogenicity of both nematodes in winter was lower than in summer. In opening space trials, when inoculated 3rd instar larvae with S. abbasi and S. carpocapsae at 300 and 500 IJs/ml, the cumulative mortalities resulted from applications in the morning and evening were not significantly different between two treatments. The LT50 values infected with S. abbasi at the same concentrations in the morning were 46.6 and 48.1 h, respectively, while those in the evening were 57.8 and 45.1 h, respectively. In S. carpocapsae, the LT50 values in the morning were 38.4 and 34.9 h, respectively, while those in the evening were 37.3 and 41.2 h, respectively. Therefore, it is suggested that both EPNs are potential to be applied as biocontrol agents against O. postica in field conditions.