Thesis (MScConsEcol (Conservation Ecology and Entomology))--University of Stellenbosch, 2009. / ENGLISH ABSTRACT: Pseudococcus viburni (Signoret) (Hemiptera: Pseudococcidae) (obscure mealybug),
is a common and serious pest of apples and pears in South Africa. Consumer and
regulatory pressure to produce commodities under sustainable and ecologically
compatible conditions has rendered chemical control options increasingly limited.
Information on the seasonal occurrence of pests is but one of the vital components of
an effective and sustainable integrated pest management system needed for
planning the initiation of monitoring and determining when damage can be expected.
It is also important to identify which orchards are at risk of developing mealybug
infestations while development of effective and early monitoring tools for mealybug
populations will help growers in making decisions with regards to pest management
and crop suitability for various markets. It is also essential to determine the presence
and efficacy of naturally occurring biological control agents in orchards so as to
ascertain the potential of biological control as a viable alternative in orchards.
However, under the current integrated pest management protocol, it has been
difficult to determine this, due to the sporadic and relatively low incidence of
mealybug infestations in some orchards, or by simply relying on naturally occurring
field populations of biocontrol agents. Knowledge of the environmental conditions
under which P. viburni population levels may become destructive is also essential for
timing the release of insectary reared natural enemies as well as understanding the
population ecology of this pest and its natural enemies. Information was gathered
regarding the seasonal phenology of P. viburni and its natural enemies in pome fruit
orchards in the Western Cape Province during the 2007/08 and 2008/09 growing
seasons. Seasonal population studies showed that P. viburni has multiple
overlapping generations with all life stages present throughout the year. The highest
orchard infestations occurred during the summer period until early winter (January to early June). This was followed by a decrease in population from late June to
November, before another increase in December. Presence-absence sampling of
mealybugs on the host plant revealed that woody parts of the tree, such as the trunk
and old stems were the most preferred sites for mealybug habitation, due to the
availability of protected refuge sites. Migration of mealybug populations to newer
growth and the upper sections of the tree crown, such as the new stems, leaves and
eventually the fruit, was observed from December throughout the summer period
until the early winter in June. Fruit colonization in both apples and pears commenced
in January, when the fruit had developed a size sufficient for P. viburni to penetrate
and occupy spaces such as the fruit core, calyx and stem end. There was no
evidence of P. viburni occurring beneath the soil surface or on the roots of host trees.
Two natural enemies of mealybugs, namely Pseudaphycus maculipennis (Mercet)
and Coccidoxenoides perminutus (Girault), were found to be active in apple and pear
orchards in the Western Cape. However, the status of C. perminutus as a parasite of
P. viburni still needs to be verified despite evidence of emergence from P. viburni
mummies, which was not sufficient enough to suggest that it is a useful biological
control agent. Seasonal abundance trends of the two natural enemies revealed that
their lifecycle is synchronized with that of the host. However, there was no evidence
of P. maculipennis activity in Ceres. No predators were found during the course of
this study. The rate of P. viburni parasitism at harvest was 46.52%, with P.
maculipennis and C. perminutus constituting 98.966% and 1.034% of the parasitoids
recovered from mealybug mummies, respectively. Studies on the use of pheromone
traps as early monitoring tools for P. viburni showed that there was a positive and
significant relationship between the fruit infestation and number of P. viburni adult
males caught in pheromone-baited traps (r2 = 0.454). The action threshold level was
estimated to be 2.5 male P. viburni caught per trap per fortnight at an economic
threshold of 2% fruit infestation. / AFRIKAANSE OPSOMMING: Pseudococcus viburni (Signoret) (Hemiptera: Pseudococcidae) (ligrooswitluis), is ‘n
algemene en ernstige plaag van appels en pere in Suid-Afrika. Druk deur verbruikers
en regulasies om kommoditeite onder volhoubare en ekologies verenigbare
toestande te produseer het chemiese beheeropsies toenemend beperk. Inligting oor
die seisoenale voorkoms van plae is een van die essensiële komponente van ‘n
effektiewe en volhoubare geïntegreerde plaagbestuurprogram. Dit is in die
aanvanklike beplanning van monitering en om te bepaal wanneer skade verwag kan
word. Dit is ook belangrik om boorde vroegtydig te identifiseer wat die risiko het om
witluisbesmettings te ontwikkel. Die ontwikkeling van effektiewe en vroeë
moniteringstegnieke vir witluisbevolkings sal produsente help met besluitneming
rakende plaagbestuur en die geskiktheid van gewasse vir verskeie markte. Dit is ook
noodsaaklik om die teenwoordigheid en effektiwiteit van biologiese beheer agente
wat natuurlik in boorde voorkom te bepaal ten einde die potensiaal van biologiese
beheer as ‘n lewensvatbare alternatief vas te stel. Onder die huidige geïntegreerde
plaagbestuurprotokol was dit egter moeilik om laasgenoemde te bepaal weens die
sporadiese en relatiewe lae voorkoms van witluisbesmettings in sommige boorde of
deur bloot staat te maak op die veldpopulasies van biologiese beheer agente wat
natuurlik voorkom. Kennis van die omgewingstoestande waaronder P. viburni
bevolkingsvlakke skadelik raak is ook noodsaaklik vir die beplanning van vrylating
van biologiese beheer agente, asook om die bevolkingsekologie van hierdie plaag en
sy natuurlike vyande te verstaan. Inligting oor die seisoenale fenologie van P. viburni
en sy natuurlike vyande in sagtevrugte boorde in die Westelike Kaapprovinsie is
gedurende die 2007/08 en 2008/09 groeiseisoene versamel. Seisoenale
bevolkingstudies het getoon dat P. viburni verskeie oorvleuelende generasies het
met alle stadia teenwoordig regdeur die jaar.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/2620 |
| Date | 12 1900 |
| Creators | Mudavanhu, Pride |
| Contributors | 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 | English |
| Detected Language | English |
| Type | Thesis |
| Rights | University of Stellenbosch |
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