Thesis (MScAgric (Conservation Ecology and Entomology)--University of Stellenbosch, 2009. / ENGLISH ABSTRACT: The obscure mealybug, Pseudococcus viburni (Signoret) (Pseudococcidae), is one of the
common and serious pests of apples and pears in South Africa. The management of this pest in
South Africa is dominated by the use of insecticides, while research into using natural enemies for
biological control of mealybugs is still ongoing. Increasing concern over the environmental impact,
pesticide residues in fruits, resistance, and expense associated with frequent use of insecticides
make it necessary to investigate alternative biological control methods, such as the use of
entomopathogenic nematodes, for the control of mealybugs. Entomopathogenic nematodes have
proven comparable or even superior to chemicals in controlling certain insect pests, without
residue problems or a harmful effect on the environment.
An important aspect of using endemic nematodes includes the identification of species of
nematodes and their symbiotic bacterial cells. A study was carried out to describe a new species
of Steinernema, which was recovered during a previous survey in citrus orchards in three
provinces of South Africa. Morphometrics, morphology, crossbreeding, drawings, light microscopy
and 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 of
Steinernema khoisanae (SF87) and Heterorhabditis zealandica (J34). Different cryoprotectants
used 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. khoisanae
after a four-day incubation period in 15% glycerol. This technique has been used for the
cryopreservation of H. zealandica, with a 78% survival rate. The thawed nematodes of both
species were able to infect Galleria mellonella larvae after 42 days of cryopreservation (-196ºC)
and were able to complete their life cycles. / AFRIKAANSE OPSOMMING: Die ligrooswitluis, Pseudococcus viburni (Signoret) (Pseudococcidae), is een van die
algemene en ernstige peste van appels en pere in Suid-Afrika. Die bestuur van hierdie pes word
tans in Suid-Afrika deur die gebruik van insekdoders gedomineer terwyl navorsing oor die gebruik
van natuurlike vyande vir die beheer van P. viburni nog aan die gang is. Die verhoogde kommer
oor die omgewing, residue in vrugte, weerstand, en die koste verbonde aan die gereelde gebruik
van chemiese middels maak dit nodig om alternatiewe biologiese metodes van beheer, soos die
gebruik van entomopatogeniese nematodes vir die beheer van witluis, te ondersoek. In ander
lande is reeds aangetoon dat entomopatogeniese nematodes onder sekere omstandighede en vir
sekere insekte gelykwaardige of selfs beter beheer kan gee as chemiese middels.
ʼn Belangrike aspek van die gebruik van endemiese nematodes vir die beheer van insekte
sluit die korrekte identifikasie van die spesies met hul geassosieerde bakteriese simbionte in. ʼn
Nuwe spesie van Steinernema is uit ʼn vorige opname van entomopatogeniese nematodes in
sitrusboorde in drie provinsies van Suid-Afrika geïsoleer. Morfometrie, morfologie, kruisteling,
ligmikroskoop en SEM fotografie is gebruik om ʼn nuwe spesies te beskryf.
ʼn Kriopreserveringsmetode is ontwikkel en ge-optimaliseer vir die langtermyn bewaring van
Steinernema khoisanae (SF87) en Heterorhabditis zealandica (J34). Verskillende
kriobeskermingsmiddels insluitend 15% gliserol, 8% dimetiel sulfokied (DMSO) en 8% etileen
glikol, waarin S. khoisanae vir periodes van twee, drie, vier, en vyf dae geïnkubeer is, is teen
kamertemperatuur, getoets, gevolg deur ʼn metanolbad. Optimum oorlewing van 69% is verkry vir
S. khoisanae nadat die infektiewe larwes (IJ) vir vier dae in 15% gliserol gehou is. Hierdie tegniek
is ook toegepas op H. zealandica, met 78% oorlewing van die IJ. Die ontvriesde nematodes van
beide spesies was in staat om Galleria mellonella larwes suksesvol te infekteer en hulle
lewensiklus te voltooi nadat hulle vir 45 dae onder kriopreservering gehou is teen -196ºC.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/2463 |
| Date | 12 1900 |
| Creators | Stokwe, Nomakholwa Faith |
| Contributors | Malan, A. P., Addison, P., University of Stellenbosch. Faculty of Agrisciences. Dept. of Conservation Ecology and Entomology. |
| Publisher | Stellenbosch : University of Stellenbosch |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | Unknown |
| Type | Thesis |
| Rights | University of Stellenbosch |
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