Richou Han, Xuehong Qiu
Guangdong Entomological Institute, China

Entomopathogenic nematodes (EPNs)Heterorhabditis and Steinernema are safe, effective and commercial bioinsecticides for many economically important pests while also maintaining a mutualistic association with the Enterobacteriaceae bacteria Xenorhabdus and Photorhabdus, respectively. Due to the economic, human health and environmentalimportance of substituting traditional chemical control methodsby biological agents, EPNs have gained recognition because oftheir effectiveness, speed of action, innocuousness to mammalsand simplicity in mass production and application.Progress on identification and classification, bacteria-neamtode symbiosis,mass production and application technology of EPNs has been made and promoted its commercialization.
Identification and taxonomy:Surveys of EPN and their symbiotic bacteria throughout the country were conducted. A large amount of EPNs and their symbiotic bacteria were collected and isolated and introduced form abroad. In addition, EPNs were identified and classified by the morphology, biology and molecular biology techniques. More than 20 species of EPNs were described and published.
Bacteria-nematode symbiotic interaction: The following four aspects are involved in this mutualisticinteraction between the bacteria and nematodes: (1) food signals produced by the bacteria to induce development of the infective juveniles (IJs) of nematodes, (2) nutrients produced by the bacteria to facilitate growth and development of the nematodes, (3) colonization and growth of the bacteria within the IJ stage of the nematodes, (4) nematicidal toxin produced by the bacteria to kill non-symbiotic nematodes. Research on the four aspects was carried out to further illuminate the mechanism of the symbiosis and the specificity of nutritional dependence between entomopathogenic nematodes and their symbiotic bacteria.
Mass production: The factors influencing the production efficiency were explored, including medium development, optimization of the culture parameters (gas supply, inoculum size, bacterial status, temperature, etc.), recovery of the infective juvenile (IJ) inocula, and formation of the IJs, extraction and harvest of IJs. A company called Century Horse Development Ltd, under the guidance of Guangdong Entomological Institute, is running. Healthy and reasonable products in solid culture system are provided for field trials in China and for internal and international markets. Production cost is still a limiting factor for further commercial development in the world nematode-based market.
Application: Ideal pest targets for these nematodes were evaluated. Apart from the important insect pests (such as flee beetle Phyllotretastriolata, and chive midge Bradysiaodoriphaga) in vegetables, new invasive pests such as the oriental fruit fly Bactroceradorsalis(Hendel), asiatic palm weevil Rhabdosceluslineaticollis (Heller) and banana moth Opogonasaccchari (Bojer) were also controlled by EPNs. In addition, transgenic Enterobacter cloacae with the insecticidal tcdA1B1 from symbiotic bacteria of EPNs was constructed and used for termite control. The transgenic bacteria also showed high toxic potential against Spodopteraexigua, S. litura andP. striolata.