Entomopathogenic nematodes : characterization of a new species, long–term storage and control of obscure mealybug, Pseudococcus viburni (Hemiptera: Pseudococcidae) under laboratory conditions

[摘要] ENGLISH ABSTRACT: The obscure mealybug, Pseudococcus viburni (Signoret) (Pseudococcidae), is one of thecommon and serious pests of apples and pears in South Africa. The management of this pest inSouth Africa is dominated by the use of insecticides, while research into using natural enemies forbiological control of mealybugs is still ongoing. Increasing concern over the environmental impact,pesticide residues in fruits, resistance, and expense associated with frequent use of insecticidesmake it necessary to investigate alternative biological control methods, such as the use ofentomopathogenic nematodes, for the control of mealybugs. Entomopathogenic nematodes haveproven comparable or even superior to chemicals in controlling certain insect pests, withoutresidue problems or a harmful effect on the environment.An important aspect of using endemic nematodes includes the identification of species ofnematodes and their symbiotic bacterial cells. A study was carried out to describe a new speciesof Steinernema, which was recovered during a previous survey in citrus orchards in threeprovinces of South Africa. Morphometrics, morphology, crossbreeding, drawings, light microscopyand Scanning Electron Microscopy (SEM) photographs were used to describe the new species.A cryopreservation method has been simplified and optimised for the long-term storage ofSteinernema khoisanae (SF87) and Heterorhabditis zealandica (J34). Different cryoprotectantsused included 15% glycerol, 8% ethylene glycol and 8% dimethyl sulfoxide (DMSO), in which S.khoisanae was incubated at room temperature for periods of two, three, four and five days,followed by a methanol wash. An optimum survival rate of 69% was obtained for S. khoisanaeafter a four-day incubation period in 15% glycerol. This technique has been used for thecryopreservation of H. zealandica, with a 78% survival rate. The thawed nematodes of bothspecies were able to infect Galleria mellonella larvae after 42 days of cryopreservation (-196ºC)and were able to complete their life cycles.

[发布机构] Stellenbosch University