Developmental Temperature Effects on Five Geographic Isolates of the Entomopathogenic Nematode Steinernema feltiae (Nematoda: Steinernematidae)

Abstract

The development of five geographic isolates of Steinernema feltiae at 5, 8, 10, 15, 20, 25, and 28°C in wax moth, Galleria mellonella, larvae was examined. The isolates were from Mediterranean (Sinop from Turkey, SN from France, and Monterey from California), subtropical (Rafaela from Argentina), and tropical (MG-14 from Hawaii) regions. All isolates caused 100% mortality of wax moth larvae and developed and produced progeny between 8 and 25°C. At 28°C, mortality was 100%, but no progeny was observed. The highest infective juvenile production was observed at 15°C for all isolates. In general, the tropical isolate, MG-14, had the lowest production of infective juveniles. The time of emergence of the infective juveniles from the host cadaver showed some differences among isolates, with the Sinop isolate having the earliest emergence time from cadavers at 15°C (10 days) and 20°C (8 days). At 25°C, the infective juveniles of the Sinop, SN, and Rafaela isolates emerged from the cadavers from 5 to 7 days. Time of host death by all isolates showed no differences at 8, 10, 15, 20, and 28°C. At 25°C for all isolates (except the MG-14), shorter times to host death were observed. Host death occurred at 12 days at 8°C, 9 to 11 days at 10°C, 4 to 5 days at 15°C, 3 days at 20°C, and 2 days at 25 and 28°C. For penetration efficiency, the Sinop, SN, and Rafaela isolates penetrated their hosts at 5, 8, and 10°C. Penetration of the infective juveniles was consistently high for all isolates at 15, 20, 25, and 28°C, but it was significantly lower for the MG-14 isolate at 15, 25, and 28°C. No progeny production occurred at 28°C, but nematode penetration did occur with the MG-14 isolate having significantly lower penetration than the other isolates. When nematodes were produced at 8, 15, and 23°C in wax moth larvae, all isolates had infective juveniles with longer body lengths at 8°C followed by 15 and 23°C. To further verify body length at the different temperatures, beet armyworm, Spodoptera exigua, larvae and dog-food agar medium were used, respectively, for in vivo and in vitro culture of the Sinop isolate. Infective juvenile body length showed the same trends, with the longest being at 8°C and decreasing in length from 15 to 23°C. The data suggest that quality of food for the nematode and temperature (that is, developmental time) influence the body length of the infective juvenile.