Pathogenic evaluation of two entomopathogenic nematodes, Steinernema abbasi and Steinernema carpocapsae, against Blattella germanica

Abstract

Pathogenicity of the entomopathogenic nematodes, Steinernema abbasi and S. carpocapsae, against the German cockroach, Blattella germanica, was conducted in this study. Adult males, females, and last nymphs of B. germanica were inoculated with 2,654 IJs/cm2 S. abbasi and S. carpocapsae, respectively, at 25 ± 2°C. The LT50 values against these three stages treated with S. abbasi were 77.7, 44.4, and 116.2 h, respectively, whereas those treated with S. scarpocapsae were 29.4, 22.2, and 43.2 h, respectively. These results showed that the LT50 values of S. carpocapsae were significantly shorter than those of S. abbasi to B. germanica, and that the LT50 values of two entomopathogenic nematodes to adult females were shorter than males and last stage nymphs, suggesting that adult females was more sensitive to nematodes than others. After storing for 0, 1, and 2 months, the mortalities of adult males caused by S. abbasi were 63, 16.7, and 5%, respectively, whereas those caused by S. carpocapsae were 100, 80, and 66.7%, respectively, at 4th day post-inoculation. The pathogenicity and persistance of S. carpocapsae were better than S. abbasi at 25 ± 2°C. Dog foods and cockroach feces extracts were placed in nematode traps for evaluating the killing activity of these two nematodes. The cumulative mortality of B. germanica treated with S. abbasi traps for 4 days was 0.8 - 4.2%, while that treated with S. carpocapsae was 55.6 - 76.7%. In contact tests, S. carpocapsae caused higher mortality (23.8 - 46.3%) than S. abbasi (1.25 - 15%) after incubation for 4 days, revealing that S. carpocapsae could infect B. germanica in 10 seconds and caused 23.8% mortality, suggesting that entomopathogenic nematodes can effectively infect B. germanica in few seconds. These results showed that the nematode traps were useful for killing B. germanica, especially using S. carpocapsae.

以蟲生線蟲Steinernema abbasi及S. carpocapsae對德國蜚蠊(Blattella germanica)進行致病力測試，用線蟲濃度2,654 IJs/cm2 接種德國蜚蠊，得到S. abbasi對雄成蟲、雌成蟲、末齡若蟲的LT50分別為77.68、44.36、及116.23 h，而S. carpocapsae所需之LT50則分別為29.4、22.19、及43.21 h。由此可知S. carpocapsae對德國蜚蠊的LT50明顯短於S. abbasi，而兩種線蟲對德國蜚蠊之LT50皆為末齡若蟲 > 雄成蟲 > 雌成蟲，故末齡若蟲感性最低，雌成蟲感性高。而在S. abbasi及S. carpocapsae的持續力試驗中，在保存0、1、或2個月後，對德國蜚蠊雄成蟲在接種後第4天造成的累積死亡率，分別為63、16.7、5%及100、80、66.7%，S. carpocapsae所引起的累積死亡率明顯高於S. abbasi，此顯示S. carpocapsae有較好持續力。在陷阱中，放置乾狗糧、乾狗糧加德國蜚蠊糞便浸出物、浸出物及無添加組共4種處理，S. abbasi對德國蜚蠊在4天後，所得之死亡率分別為4.2、1.7、0.8、及3.3%，明顯低於S. carpocapsae之68.9、63.3、55.6、及76.7%，由此可見S. carpocapsae在實際防治德國蜚蠊的試驗中效果較好。在德國蜚蠊雄成蟲與線蟲的接觸時間測試，在第4天雄成蟲的死亡率，S. abbasi在接觸90 sec以下者，所造成的死亡率皆不超過5%，而120及150 sec分別有15及12.5%；而S. carpocapsae則為23.8~46.3%，最值得注意者為10 sec之處理組，在第4天造成23.8%的死亡率。因此可確定在極短的接觸時間，S. carpocapsae已經能對德國蜚蠊侵染致死。本試驗結果顯示蟲生線蟲對德國蜚蠊具有良好之殺蟲效力。