Abstract:

 【Aim】To investigate the effects of insulin on the growth and development of the entomopathogenic nematode Steinernema kraussei 0657Land its symbiotic bacteria. 【Methods】 The 3rd instar larvae of Galleria mellonella were infected with 1.5 mL of 3 000/mL S. kraussei 0657Lsuspension, the symbiotic bacteria  Xenorhabdus bovenii 0657Lwas isolated from S. kraussei 0657Lafter 24 h culture at25 ℃. S. kraussei 0657Lwas fed with X. bovenii 0657Ltreated with 1:500 and 1:5 000 insulin, respectively, the colony diameter and growth rate of X. bovenii 0657Lwere measured by stereomicroscope at1‒6 d after insulin treatment, the lifespan, survival rate, number of head swing per 30 s and number of swallows per 30 s of S. kraussei 0657Lwere calculated to evaluate its average lifespan, locomotion and swallowing ability. 【Results】 The colonial diameters of X. bovenii 0657Lin 1:5 000 insulin and 1:500 insulin treatment groups were increased by 77.2% and 54.0%, respectively, during the logarithmic growth period (at 2 d after treatment) as compared with that of the blank control group. The growth rates of X. bovenii 0657Lin 1:5 000 insulin and 1:500 insulin treatment groups were increased from 68.0 µm/d of the blank control group to 120.4 and 104.7 µm/d, respectively. The lifespans of S. kraussei 0657Lin 1:5 000 insulin and 1:500 insulin treatment groups were increased by 27.3% and 45.5%, respectively as compared with that of the blank control group. The numbers of head swing per 30 s of the 3rd instar larvae of S. kraussei 0657Lin 1:5 000 insulin and 1:500 insulin treatment groups were increased by 56.3% and 74.7%, respectively, compared with that of the blank control group. The numbers of swallows per 30 s of the 3rd and 4th instar larvae and adults of S. kraussei 0657Lin 1:5 000 insulin and 1:500 insulin treatment groups were increased by 50.9% and 65.5%, 26.8% and 35.2%, 23.7% and 21.1%, respectively, as compared with that of the blank control group.【Conclusion】Insulin can significantly promote the growth and increase the growth rate of single colony of the symbiotic bacteria X. bovenii 0657Lof S. kraussei 0657Lwhich can prolong the lifespan of S. kraussei 0657Land improve the locomotion and swallowing ability of entomopathogenic nematode indirectly. The results of this study can provide a scientific basis for extending the shelf life of entomopathogenic nematodes and provide a theoretical basis for efficient biological control of entomopathogenic nematodes.

Key words: Steinernema kraussei; Xenorhabdus bovenii; insulin, entomopathogenic nematodes, symbiotic bacteria, growth and development, lifespan, locomotion, swallow