LOW-TEMPERATURE ACTIVITY IN HETERORHABDITIS SP (NEMATODA, HETERORHABDITIDAE)

Four isolates of Heterorhabditis sp. (H181, Hf85 and Hnh1 86 from the Netherlands and K122 from Ireland) were compared in laboratory bioassays. Galleria mellonella larvae were exposed to infective juveniles in sand for 2-5 days. There were significant differences between isolates in the number of infective juveniles that found and entered the larvae at 9-degrees and 12-degrees-C. At 9-degrees-C, Hf85 was significantly better than all the other isolates. Success of Hf85 was considerably reduced at 7-degrees-C, and there was no parasitisation at 5-degrees-C. The infectivity for late instar Tenebrio molitor larvae was tested on filter paper at 5-degrees, 7-degrees, 9-degrees, 12-degrees, and 20-degrees-C. There was no mortality at 5-degrees-C. At 7-degrees-C, the LD50 of Hf85 was 23 IJs/insect; this was significantly lower than for the other three isolates. The LD50s of isolates differed significantly at 9-degrees and 12-degrees but not at 20-degrees-C. Differences between LT50s were significant at 20-degrees-C. The rank order of efficacy of the three Dutch isolates in the bioassays was the same as that established by other authors in pot trials at low temperature.