兩種蟲生線蟲Steinernema abbasi及S. carpocapsae對埃及斑蚊（雙翅目：蚊科）致病力之比較

Abstract

The present study focused on comparing virulence of two entomopathogenic nematodes, Steinernema abbasi and S. carpocapsae, to the mosquito, Aedes aegypti. The results showed that the first instar larvae and pupae of Ae. aegypti were not susceptible to both nematodes. The cumulative mortalities inoculated with 300 infective juveniles (IJs) per larva of S. abbasi against second to fourth instar larvae of Ae. aegypti were 21.1, 30.0, and 97.8%, respectively, whereas those inoculated with S. carpocapsae were 45.6, 94.4, and 97.8%, respectively. The LT50 values of older instar larvae inoculated with both nematodes were shorter than those of younger instars. The LD50 values of fourth instar larvae inoculated with S. abbasi and S. carpocapsae were 122.6 and 44.5 IJs/larva at 48 h after inoculation. Encapsulated nematodes were calculated from dead third or fourth instar larvae of Ae. aepypti inoculated with 200 IJs/larva of S. abbasi or S. carpocapsae. Numbers of encapsulated S. abbasi in third and fourth instar larvae were 1-4, and 0-10, respectively, whereas those of S. carpocapsae in third and furth instar larvae were 0-9, and 0-8, respectively. However, the larvae with one nematode encapsulated were mostly observed. The cumulative mortalities of fourth instar larvae inoculated with S. abbasi and S. carpocapsae at 25°C were 93.3 and 95.6%, respectively, while those incubated at 20°C were lowest at only 20.0 and 76.7%, respectively. The mortalities of fourth instar larvae when inoculated with both nematodes immersed previously in four different depths of water were not significantly different. The cumulative mortalities of fourth instar larvae inoculated with both S. abbasi and S. carpocapsae which had been placed in water in a longer diameter of round plate were lower than those in a shorter diameter. The LT50 value of fourth instar larvae inoculated with S. carpocapsae in a longer diameter of round plate was longer than that in a shorter one. The mortalities of fourth larvae inoculated with both S. abbasi and S. carpocapsae, which had been kept in water for 10 or 20 days, were 33.3-48.9 and 80.0-85.6%, respectively, being not significantly different between treatments within the same species. However, the mortalities resulted from inoculations with those nematodes kept in water for 30 days were significantly lower than those for 10 and 20 days. In addition, the LT50 value of fourth instar larvae inoculated with S. carpocapsae kept for 20 days was longer than that for 10 days. Therefore, our experimental data provide information for further studies on potential application of the entomopathogenic nematodes as biological control agents against mosquitoes.