Entomopathogenic nematodes (Steinernema spp.) are used in integrated pest management to control insect pests in cryptic environments. The nematodes are mass produced in monoxenic liquid culture with their symbiotic bacteria Xenorhabdus spp. For a better understanding of nematode population dynamics, the life history traits (LHTs) of the entomopathogenic nematode Steinernema feltiae were assessed at 25 °C by observing single pairs of male and female nematodes using a hanging drop technique. To investigate the influence of different food supplies on nematode reproduction, the LHTs were assessed with a daily supply of 5 ×, 10 × and 20 × 10(9) cells ml(-1) of the nematode's bacterial symbiont Xenorhabdus bovienii in semi-solid nematode growth gelrite (NGG) medium. Increasing bacterial density had a significant positive influence on the average number of offspring produced, which ranged from 359 to 813 per female. The intrinsic rate of natural increase r m, which ranges from 1.10 to 1.19 day(-1), was neither influenced by the bacterial density, nor was the mean generation time T (5.12-5.25 days) and population doubling time (PDT) (0.64-0.59 days). The average lifespan of reproductive females, which ranged from 6.7 to 7.3 days, was positively correlated with bacterial density. A positive correlation between female body volume and bacterial density was recorded (R = 0.67) as well as a significant positive correlation between female body size and offspring production (R = 0.89) in hanging drops. Whether these data can be used to predict nematode yields in liquid culture was tested. The total female body volume calculated as the average female body volume × total number of parental females per millilitre 3 days after nematode inoculation was positively correlated (R = 0.72) with nematode yields. The total female body volume on process day 3 is thus a good indicator for the estimation of nematode yield at the end of the process (12-15 days post dauer juvenile (DJ) inoculation) in both Erlenmeyer flasks and bioreactors. With a mean deviation of 9467 DJs ml(-1), the error resembles approximately 5 % of the final DJ yields.
Life history traits (LHT) of Steinernema riobrave strain Sr 7-12 and Sr HYB19 were assessed at 25°C in monoxenic culture using a hanging drop technique. The LHT were studied with 5 x 109, 10 x 109 and 20 x 109 cells m l-' of Xenorhabdus cabanillasii in semi-solid Nematode Growth Gelrite. Increased X. cabanillasii densities had a significant positive influence on offspring production on both Sr 7-12 and the hybrid Sr HYB19. At the higher bacterial food density, the total fertility rate (TFR) per female of Sr 7-12 was 2022 offspring and the net reproductive rate (R0) reached 1904 offspring. Similarly, for Sr HYB19, the TFR per female was 2434 and Ro was 1903. The percentage offspring produced via intra-uterine development (endotokia matricida) was relatively higher at 5 x 109 bacterial cells ml-1 than at higher bacterial density, with 64% and 66% of the total offspring produced by Sr 7-12 and Sr HYB19, respectively. A positive correlation (R = 0.648) was recorded for offspring production and bacterial food density and for female body volume with bacterial density (R = 0.610). Female nematodes survived longer at higher bacterial food density; however, females of both strains could not survive longer than 7.8 days, beginning from hatching and always ending 1 day after initiation of endotokia matricida. Based on LHT results, there is a potential to maximise yield of dauer juveniles in liquid culture through increasing bacterial food density.
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