Life history traits of entomopathogenic nematodes of Steinernema spp. and Heterorhabditis bacteriophora
Entomopathogenic nematodes (EPNs) are lethal pathogens of insect pests. Steinernema feltiae and H. bacteriophora are the most widely spread EPN species in the world. On the other hand S. riobrave and S. yirgalemense are limited to tropical climates. Investigations of the life history traits (LHT) of S. feltiae, S. riobrave, S. yirgalemense and H. bacteriophora in hanging drops using semi-solid nematode growth gelrite with their respective symbionts were conducted. The hanging drop method allowed investigating the LHTs of the four EPN species based on individual females/hermaphrodites at different bacterial densities. Offspring production has increased with increased bacterial density. The increase in offspring production was found significantly associated with the body volume of females recorded at the beginning of endotokia matricida. Endotokia matricida is internal hatching of juveniles inside the uterus followed by complete consumption of the maternal nematode body content, which occurs in all fertile females/hermaphrodites of EPNs assessed. The presence of significant correlation between body size of female nematodes and offspring production in hanging drops indicated the possibility to estimate DJ yield in liquid culture. In liquid culture, food is the limiting factor since the culture method does not allow providing fresh food every day like in hanging drops. As a consequence of competition, the number of maternal nematodes has a significant negative correlation with offspring production per female. However, it was demonstrated that the total female body volume is a good parameter for DJ yield estimation in liquid culture with acceptable degree of error. This model could be improved further by including bacterial cell numbers at the beginning of endotokia matricdia, which is linked with second generation development of adults.