Dissertation (PhD)--University of Stellenbosch, 2003. / ENGLISH ABSTRACT: A survey was conducted in the Western Cape Province during the 1999/2000
and 2000/2001 seasons on mealybugs occurring in vineyards. P/anococcus
ficus (Signoret) was the dominant mealybug in vineyards during this time.
During this study P. ficus was recorded for the first time on roots of
grapevines, which has far reaching implications for the control of this
important vine leafroll virus vector as control actions were focused on above
ground control. Other mealybugs presently recorded in local vineyards
included Pseudococcus /ongispinus (Targioni) and Ferrisia ma/vastra
(McDaniel). Pseudococcus viburni (Maskell) and Ps. so/ani Ferris were found
on weeds in vineyards. Natural enemies of P. ficus recorded most frequently
were species of Nephus predatory beetles, and the parasitaids
Coccidoxenoides peregrinus (Timberlake), Anagyrus sp. and Leptomastix
dacty/opii (Howard).
Developmental studies on P. ficus and C. peregrinus indicated that the
intrinsic rate of increase (rm) was similar, peaking at 25°C (rm = 0.169 for P.
ficus; rm = 0.149 for C. peregrinus). The net replacement rate (Ra) was higher
for P. ficus than for C. peregrinus at all five temperatures tested. The Ra for
P. ficus reached a maximum at 21°C (308.87) and C. peregrinus at 25°C for
C. peregrinus (69.94). The lower and upper thresholds for development of P.
ficus were estimated at 16.59 and 35.61°C respectively. The lower threshold
for development of C. peregrinus was 8.85°C. These parameters indicated
that both insects were well adapted to temperatures in the Western Cape Province. The lower minimum threshold temperature of C. peregrinus in
relation to that of P. ficus suggests that C. peregrinus should be more active
during winter and early spring than P. ficus.
A central systematic presence-absence sampling system was developed for
P. ficus. Monitoring three different plant parts on the vine indicated that new
growth areas on vines adjacent to the main stem could serve as an early
warning system for pending P. ficus bunch infestations. Intervention should
be planned when 2 % of the stems are infested with P. ficus when using this
system.
Seasonal population studies of P. ficus and its natural enemies showed that
stem infestation by P. ficus reached peak levels during January in Robertson
and Stellenbosch and during February in the Hex River Valley. Vine
mealybugs colonised new growth early in the season, followed by the leaves
and eventually the bunches towards the end of the season. High stem
infestations early in the season resulted in high bunch infestation levels at
harvest. A density dependent relationship was evident between P. ficus
populations and parasitoid populations, suggesting that the parasitoids played
a mayor role in the biological control of P. ficus populations. Biological control
was however only achieved towards the end of the season when damage to
the crop had already occurred.
Mass releases of C. peregrinus on P. ficus populations were done in order to
augment biological control as an alternative to chemical control. Between five and six releases of 20 000 C. peregrinus per release were done at monthly
intervals in three grapegrowing areas. Mass released C. peregrinus
controlled P. ficus adequately in the Hex River Valley. Control of P. ficus
using this approach was no worse than using chemical control in Robertson
and Stellenbosch. C. peregrinus is commercially available and can therefore
be used as an alternative to chemical control by producers.
Degree day estimation was used to predict development of P. ficus
populations. This information was used as an input in a P. ficus pest
management model. Data acquired from P. ficus and ant monitoring were
used as components to construct a decision chart. This chart can be used by
producers to optimise the control of P. ficus populations using either chemical
control or mass releases of C. peregrinus. / AFRIKAANSE OPSOMMING: "n Studie is gedurende die 1999/2000 en 2000/2001 seisoene gedoen met die
doelom die witluisspesies wat in wingerde voorkom, te identifiseer.
Planococcus ficus (Signoret) is tans die dominante witluisspesie in wingerde
in die Wes Kaap Provinsie. P. ficus kolonies is op wingerdwortels gevind.
Dié bevinding kan verreikende gevolge hê vir die beheer van dié plaag as "n
belangrike rolbladvirus vektor aangesien beheer tot dusver gefokus het op
bogrondse gedeeltes. Ander witluisspesies wat in wingerde gevind is, sluit in
Pseudococcus /ongispinus (Targioni) en Ferrisia malvastra (McDaniel).
Pseudococcus vibumi (Maskell) en Ps. so/ani Ferris is op onkruide in
wingerde gevind. Dominante natuurlike vyande van P. ficus sluit predatoriese
kewertjies van verskeie Nephus spp. en die parasitoïede Coccidoxenoides
peregrinus (Timberlake), Anagyrus sp. en Leptomastix dacty/opii (Howard) in.
Ontwikkelingstudies op P. ficus en C. peregrinus het aangetoon dat die
inhirente voortplantingstempo (rm) soortgelyk was vir beide insekte met "n
maksimum by 25°C (0.169 vir P. ficus, 0.149 vir C. peregrinus). Die netto
vervangingstempo (Ra) was in vergelyking met C. peregrinus hoër vir P. ficus
by al vyf temperature getoets. Die Ra van P. ficus het "n maksimum bereik
teen 21°C (308.87) en die van e. peregrinus by 25°C (69.94). Die teoretiese
hoër en laer drempels vir ontwikkeling van P. ficus was onderskeidelik 16.59
en 35.61 oe. Die teoretiese laer drempelwaarde van ontwikkeling vir e.
peregrinus was 8.85°e. Hierdie parameters dui aan dat beide insekte goed
aangepas is by temperature in die Wes Kaap Provinsie. Die laer minimum drempel vir ontwikkeling van C. peregrinus in verhouding tot P. ficus impliseer
dat C. peregrinus in die winter en vroeë lente meer aktief sal wees as P. ficus.
'n Sentrale sistematiese aan-afwesig moniteringsisteem met bekende vlakke
van steekproefnemingsfout is ontwikkel in kommersiële wingerde vir P. ficus.
Monitering van drie verskillende dele op die wingerdstok het aangedui dat die
nuwe groei areas kan dien as 'n vroeë waarskuwing vir latere P. ficus
trosinfestasies. Dié sisteem sal produsente in staat stelom te bepaal
wanneer optrede noodsaaklik is. Daar word voorgestel dat optrede
noodsaaklik is by 'n P. ficus besmettingsvlak van 2 % op die nuwe groei areas
op stokke.
Stambesmetting deur P. ficus het in Januarie piekvlakke bereik in
Stellenbosch en Robertson, en in Februarie in die Hex Rivier Vallei. P. ficus
koloniseer nuwe groei vroeg in die seisoen waarna blare en trosse aan die
einde van die seisoen gekoloniseer word. Dié data dui aan dat P. ficus
besmetting op nuwe groei vroeg in die seisoen 'n aanduiding kan gee van hoë
trosbesmetting aan die einde van die seisoen. 'n Digtheidsafhanklike
verwantskap was waarneembaar tussen P. ficus plaagpopulasies en
parasitoïed populasies. Dié verwantskap dui aan dat parasitoïede die
belangrikste rol speel in biologiese beheer van P. ficus populasies.
Biologiese beheer van witluis is egter eers aan die einde van die seisoen
bereik toe die oes reeds beskadig was.
Massavrylatings van C. peregrinus is in P. ficus besmette blokke gedoen om
biologiese beheer aan te help en sodoende as alternatief tot chemiese beheer te dien. Tussen vyf en ses vrylatings met 20 000 C. peregrinus is een keer
per maand gedurende die seisoen gedoen. Die vrygelate C. peregrinus het
P. ficus populasies voldoende beheer in die Hex Rivier Vallei. Beheer van P.
ficus deur massavrylatings van C. peregrinus was soortgelyk as chemiese
beheer in Robertson en Stellenbosch. C. peregrinus is kommersieel
beskikbaar en kan om hierdie rede as alternatief tot chemiese beheer gebruik
word.
Graaddag bepaling is gebruik om die ontwikkeling van P. ficus populasies te
voorspel. Hierdie inligting is gebruik as 'n verdere hulpmiddel in die P. ficus
plaagbeheermodel. Inligting verkry vanuit P. ficus en mier monitering is
gebruik as komponente in die opstel van 'n besluitnemingstabel. Hierdie tabel
kan gebruik word deur produsente om beheer van P. ficus plaagpopulasies te
optimaliseer deur chemiese beheer of massavrylatings van C. peregrinus.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/53361 |
| Date | 03 1900 |
| Creators | Walton, Vaughn M. (Vaughn Martin) |
| Contributors | Pringle, K. L., Barnes, B. N., 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 | English |
| Type | Thesis |
| Format | 141 p. : ill. |
| Rights | Stellenbosch University |
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