Abstract
Survival of Heterorhabditis spp. was highest at temperatures from 15-30 degrees C; with an optimal survival at 25 degrees C followed by 30, 20 and 15 degrees C. In contrast, Steinernema spp. survival was better at the lower temperatures than at the higher ones for 15 days. In all cases, temperatures above 30 degrees C were less favored for tested nematode survival. In general, heterorhabditid nematodes pathogenicities were greater at temperatures form 20-30 degrees C than at the lowest and highest temperatures (15 and 35 degrees C). Optimal pathogenicities were obtained at 25 degrees C by HP88 and at 30 degrees C by SAA2 and SI. It was also noticed that H. indices SAA2 could not induce larval mortality at temperature 15 degrees C. Analysis of data revealed significant differences at 5% level of probability in pathogenicity among the tested nematodes at all tested temperatures as well as between the tested temperatures b each nematode species; except S. carpocapsae All and S. carpocapsae S2 which showed no significant difference between each other in the pathogenicity at tested temperatures. Also, it could be concluded that the optimum temperature for steinernematids and heterorhabditids propagation (i.e. temperature at which maximum number of infective juveniles (IJs) were produced per host) was 30 degrees C; except H. bacteriophora HP88 in 4(th) larval instar of Spodoptera littoralis and S. carpocapsae All in 3(rd) larval instar of Plutella xylostella, it was at 25 degrees C.