Thesis (PhD)--University of Stellenbosch, 2000. / ENGLISH ABSTRACT: The population density of the white wax scale, Ceroplastes destructor Newstead, has
increased since 1994 in certain areas of Western and parts of Eastern Cape Provinces of
South Africa where citrus is grown, particularly on Citrus reticulata (Blanco). A study
was conducted to investigate its morphology, biology and ecology as contributions to the
development of a sound integrated management programme.
Characteristics of the immature stages and adult females were described and
illustrated from field-collected and slide-mounted specimens. A key to the different
stages and morphometeric characteristics useful for separating them are provided. No
significant differences in female fecundity were found between orchards (P > 0.05).
However, fecundity varied significantly between female size classes from the same
orchard (P < 0.001). Female body-size also differed significantly between orchards (P <
0.05) and was significantly positively correlated with fecundity (P < 0.01). C. destructor
has one discrete generation per year in South Africa. Oviposition commenced in
November and continued through to the end of December with a few females ovipositing
until mid January. Population density of the second instar peaked in February while the
third instar extended from March to the end of July, followed by a peak population of
adults in August. Seven primary and three secondary parasitoids, as well as four predator
species attacking C. destructor were identified. Aprostocetus (= Tetrastichus)
ceroplastae (Girault) was the dominant species, accounting for 78.87% of the total
primary parasitoids reared. Peak numbers of parasitoids and predators were synchronized
with peak emergence of susceptible scale stages, indicating that the host-parasitoid/predator system contained a density-dependent regulatory mechanism. Key
mortality factors varied slightly between two of the orchards. Key stage mortality
determined from a cohort life table was generally in the third instar (LIlI) and preovipositional
female (POF) stage. Significant density-dependent mortality factors were
demonstrated for the first instar (LI) and PDF stage.
Dispersal of C. destructor is by first instar nymphs and the numbers caught on a
series of yellow sticky traps varied significantly between crawler densities at the source,
trap distances and trap directions from the source (P < 0.001). The numbers caught were
positively correlated to the initial crawler density at the source (P < 0.01), suggesting that
dispersal was density dependent. Trap distance and the numbers caught were inversely
correlated (P < 0.01). Evaluation of effects of different densities of C. destructor on
growth, survivorship and reproduction of scales as well as on leaf bearing ability of trees
and area of leaf surface covered with sooty mould fungus was carried out on naturally
infested Syzygium (= Eugenia) malaccensis (L.) plants. Scale body size and fecundity
were inversely related to scale density (P < 0.01), suggesting density-dependent
intraspecific competition. Scale survivorship generally declined with increasing density
whereas scale parasitism and predation were positively correlated with density (P < 0.05).
At high scale densities production of new leaves was significantly reduced (P < 0.01),
reducing the resource base for subsequent generations of scale. Scale density and leaf
area covered with sooty mould fungus were significantly positively correlated (P < 0.05).
The toxicity of four synthetic insecticides against the three immature stages of C.
destructor and of eight insecticides against the parasitoid A. ceroplastae was evaluated.
Development of the first and second instars of C. destructor was completely arrested by the chemicals. Female fecundity, fertility and body sizes of survivors of treatments
applied at the LIII stage were not significantly affected by any of the chemicals (P >
0.05). All the chemicals exhibited high toxicity to A. ceroplastae and hence are not
recommended for integrated management of C. destructor in citrus orchards where A.
ceroplastae plays an important role. / AFRIKAANSE OPSOMMING: Die populasiedigtheid van die witwasdopluis, Ceroplastes destructor Newstead, het
sedert 1994 toegeneem in sekere gebiede van die Weskaap en Ooskaap provinsies van
Suid-Afrika waar sitrus verbou word, veralop Citrus reticulata (Blanco). 'n Studie van
hierdie insek se morfologie, biologie en ekologie is onderneem as bydrae tot die
ontwikkeling van 'n geïntegreerde bestuursprogram.
Die karaktertrekke van die onvolwasse stadia en die volwasse wyfies is beskryf
en geïllustreer vanaf eksemplare wat in die veld versamel is en op g1asplaatjies
gemonteer is. 'n Sleutel vir die verskillende stadia en morfometriese kenmerke wat nuttig
is om hulle te onderskei, word voorsien. Geen beduidende verskille in die vrugbaarheid
van wyfies van verskillende boorde is gevind nie (P < 0.05). Vrugbaarheid het egter
betekenisvol verskil by die verskillende grootteklasse van wyfies uit dieselfde boord (P <
0.001). Die liggaamsgrootte van wyfies uit verskillende boorde het betekenisvol verskil
(P < 0.05) en was betekenisvol positief gekorreleer met vrugbaarheid (P < 0.01). C.
destructor het een generasie per jaar in Suid-Afrika. Eierlegging het in November begin
en aangehou tot aan die einde van Desember, met enkele wyfies wat nog tot in middel
Januarie eiers gelê het. Die populasiedigtheid van die tweede instar het 'n hoogtepunt in
Februarie bereik, terwyl die derde instar van Maart tot aan die einde van Julie geduur het,
gevolg deur 'n piekbevolking van volwassenes in Augustus. Sewe primêre en drie
sekondêre parasitoïde asook vier predator spesies wat C destructor aanval, is
geïdentifiseer. Aprostocetus (=Tetrastichus) ceroplastae (Girault) was die dominante
spesies wat 78.87% van die totale aantal primêre parasitoïde wat uitgeteel is, uitgemaak het. Die pieke in die getalle van parasitoïde en predatore was gesinchroniseer met pieke
in die verskyning van die gevoelige stadia, wat dui op die aanwesigheid van 'n
digtheidsafhanklike regulatoriese meganisme. Die sleutel mortaliteitsfaktore het effens
gevarieer tussen twee van die boorde. Die sleutelstadium van mortaliteit, soos bepaal
m.b.v. 'n kohort lewenstabel, was gewoonlik die derde instar (LIlI) en die preoviposisionele
wyfie (POW). Betekenisvolle digtheidsafhanklike mortaliteitsfaktore IS
aangetoon vir die eerste instar (LI) en die POW.
Die verspreiding van C.destructor vind plaas deur die eerste instar nimfe en die
getalle wat op 'n reeks van taai geel valle gevang is, het betekenisvol gewissel volgens
kruiperdigthede by die bron, asook die afstand en rigting van die valle vanaf die bron (P
< 0.001). Die getalle wat gevang is, was positief gekorreleer met die aanvanklike
kruiperdigtheid by die bron (P < 0.01), wat daarop dui dat verspreiding
digtheidsafhanklik was. Die afstand van die valle en die aantal wat gevang is, was
omgekeerd gekorreleer (P < 0.01). 'n Evaluering van die invloed van verskillende
digthede van C. destructor op die groei, oorlewing en reproduksie van dopluise, asook
die vermoë van bome om blare te dra en die area van die blaaroppervlak wat met
roetskimmel besmet is, is uitgevoer op plante van Syzygium (= Eugenia) malaccensis (L.)
met 'n natuurlike besmetting. Die liggaamsgrootte en vrugbaarheid van die dopluise was
omgekeerd gekorreleer met hulle digtheid (P < 0.01), wat dui op digtheidsafhanklike
intraspesifieke kompetisie. Die oorlewing van die dopluise het oor die algemeen
afgeneem met toenemende digtheid, terwyl parasitisme en predasie positief gekorreleer
was met digtheid (P < 0.05). By hoë dopluisdigthede het die produksie van nuwe blare
betekenisvol afgeneem (P < 0.01), wat die hulpbronbasis vir daaropvolgende generasies van dopluise verswak. Die dopluisdigtheid en blaaroppervlak wat met roetskimmel bedek
was, was positief gekorreleer (P < 0.05).
Die toksisiteit van vier sintetiese insektemiddels teenoor die drie onvolwasse
stadia van C. destructor en van agt insektemiddels teenoor die parasitoïd A. ceroplastae
is geëvalueer. Die ontwikkeling van die eerste en tweede instars van C. destructor is
heeltemal stopgesit deur die middels. Die fekunditeit, fertiliteit en liggaamsgrootte van
wyfies wat toedienings op die LIIl stadium oorleef het, is nie betekenisvol ge-affekteer
deur enige van die middels nie (P < 0.05). Al die middels was baie toksies teenoor A.
ceroplastae en word dus nie aanbeveel vir die geïntegreerde bestuur van C. destructor
waar A. ceroplastae 'n belangrike rol speel nie.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/51637 |
| Date | 12 1900 |
| Creators | Wakgari, Waktola (Waktola Muleta) |
| Contributors | Giliomee, J. H., Stellenbosch University. Faculty of AgriSciences. Dept. of Conservation Ecology and Entomology. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | Unknown |
| Type | Thesis |
| Format | 210 p. : ill. |
| Rights | Stellenbosch University |
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