Environmental factors affecting sexual differentiation in the entomopathogenic nematodeHeterorhabditis bacteriophora

Abstract

The present study was aimed at determining the influence of various environmental factors on sex differentiation (SD) in the entomopathogenic nematode Heterorhabditis bacteriophora HP88 strain, under in vivo and in vitro culture conditions. Injection of individual nematodes into last instars of Galleria mellonella resulted in development of a similar number of females and hermaphrodites (35-40%) and 20-25% males. Increasing the number of nematodes injected into the insect did not change these proportions. In smaller insects (0.7-1.5 cm long), an increase in the proportion of hermaphrodites was recorded as compared with larger size cadavers (2.4-2.7 cm long). When individual hermaphrodites were placed on NGM, the proportion of hermaphrodites, females and male progeny was 63%, 31%, and 6%, respectively. Rearing on richer medium ("Dog-food" agar) resulted in reduction in the proportion of hermaphrodites. Nematodes introduced to the symbiotic bacterium obtained from other nematode strains (IS-5 and IS-33) developed similarly to the culture reared on the HP88 bacteria. Rearing the nematodes at a temperature range between 21 degrees C to 30 degrees C also did not have a significant effect on the sexual differentiation among nematodes cultured on NGM. The proportion of hermaphrodites increased as the starvation period of hatching nematode juveniles lengthened (>6 hr). The data obtained in the present study strongly suggest that the main factor affecting sex differentiation in H. bacteriophora is the nutrition source. The practical and biological implications of the results are discussed.