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A study on the application technology of the sterile insect technique, with focus on false codling moth, Thaumatotibia leucotreta (Meyrick) (Lepidoptera: Tortricidae), a pest of citrus in South AfricaNepgen, Eugene Stephan January 2014 (has links)
False codling moth (FCM), Thaumatotibia leucotreta (Meyrick) (Lepidoptera: Tortricidae) is considered the most important indigenous pest of citrus in southern Africa. Major concerns such as progressive insecticidal resistance, the negative impact of insecticides on the environment, as well as the influence of consumers opposed to chemical residues on fruit, created opportunities for biological control methods such as Sterile Insect Technology (SIT). This technology is now established in the Western and Eastern Cape provinces of South Africa as an effective, sustainable alternative to conventional FCM control methods. Due to the prevalence of the pest in all citrus producing areas of South Africa, potential for SIT to expand is enormous. Success of an SIT programme is highly dependent on efficient application of the technology to achieve its objectives in a timeous manner. The aim of this study was to advance the application of SIT for control of FCM on citrus in South Africa, by investigating the effect of certain critical stages in the process. The effect of long-distance transportation on fitness of irradiated FCM was determined, showing reduced performance with cold-immobilized transport. A significant decrease in flight ability and longevity of irradiated FCM was found, although critically, realized fecundity was not affected. The effect of two different insecticides in the pyrethroid and organophosphate chemical groups were investigated for their residual effect on mortality of released irradiated FCM, to determine if these pest control programmes could be integrated. Both chlorpyrifos and tau-fluvalinate were effective in killing irradiated FCM for a number of days after application, after which degradation of the active ingredient rendered it harmless. This effect was found to be similar for irradiated and non-irradiated males, consequently ratios of sterile : wild male FCM should be retained regardless of whether sprays are applied or not. The modes for release of sterile FCM in an SIT programme were investigated. Efficacy of ground and aerial release platforms were tested by evaluating the recovery of released irradiated male FCM in these orchards. More irradiated FCM were recovered in orchards released from the ground compared to air. However, an economic analysis of both methods shows application of irradiated insects over a large geographical area is more cost-effective by air. Depending on the terrain and size of the target area, a combination of both methods is ideal for application of SIT for control of FCM in citrus. Development of application technology for advance of the programme is discussed and recommendations for future research and development are offered.
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Dispersal of sterile false codling moth, Thaumatotibia leucotreta (Meyrick) (Lepidoptera: Tortricidae), for a sterile insect technique programme on citrusWagenaar, Gideon Daniel January 2015 (has links)
The false codling moth (FCM), Thaumatotibia leucotreta (Meyrick) (Lepidoptera: Tortricidae), is an important pest of citrus in South Africa and challenging to manage due to its inconspicuous nature. An effective method currently being employed for the area-wide suppression of the FCM is the Sterile Insect Technique (SIT) and the effective dispersal of sterile moths is very important for success with SIT. This study was conducted in the Addo area of the Sundays River Valley (Eastern Cape) where the programme is commercially used. In this study, sterile male moths were released in different orchards on a citrus farm, and in nearby veld at different times of the year, and their dispersal was monitored through the use of pheromone traps. Various climatic factors were monitored. This provided insight into the local dispersal of sterile male FCM adults in response to abiotic cues (particularly climatic factors). The movement of the FCM in four citrus cultivars, namely lemons, navel and Valencia oranges and mandarins and in the nearby veld (open field), was determined at six different stages of the year. Results clearly indicated that sterile FCM movement is concentrated within citrus orchards, as very few moths were trapped beyond 30 m from the release point, particularly in navel and Valencia orchards. Of the climatic factors measured, minimum and maximum temperatures had the most significant influence on FCM dispersal, and based on the results, various recommendations are made for the releases of sterile FCM in an area-wide SIT management programmes on citrus. A better understanding of the dispersal capabilities of the FCM in an agricultural system, under different conditions and at different times of the year, is invaluable not only in improving release strategies in an SIT programme but in planning future control strategies against the FCM.
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Epidemiology and control of Pseudocercospora angolensis fruit and leaf spot disease on citrus in ZimbabwePretorius, Mathys Cornelius 12 1900 (has links)
Thesis (MScAgric)--University of Stellenbosch, 2005. / ENGLISH ABSTRACT: Fruit and Leaf Spot Disease (FLSD) of citrus, caused by Phaeoramularia angolensis, is
found only in 18 countries in Africa, the Comores Islands in the Indian Ocean and Yemen in
the Arabian peninsula. The major citrus export countries in Africa are Morocco, South Africa,
Swaziland, and Zimbabwe. Zimbabwe is the only country affected by FLSD. FLSD is a
disease of major phytosanitary and economic importance and its devastating effect on citrus is
highlighted by the fact that the damage is cosmetic, which renders the fruit unmarketable.
Total crop losses are not uncommon in Kenya. The aims of the present study, therefore, was
was to determine the occurrence of P. angolensis in Zimbabwe and neighbouring
Mozambique, to compare these isolates with the Cercospora Fresen. isolates from Swaziland
and South Africa, to determine the epidemiology of the pathogen and to implement an
effective control strategy to prevent the spread of FLSD.
Leaf samples with citrus canker-like lesions collected in the early 1990’s in Zimbabwe
were found to be infected by the fungus, Phaeoramularia angolensis. Surveys were
undertaken to determine the spread and intensity of FLSD in Zimbabwe and Mozambique. In
Zimbabwe, P. angolensis was limited to an area above the 19° south latitude, predominantly
the moist areas and not the low-lying drier parts of the country. In Mozambique, no P.
angolensis symptoms were found. Observations during the survey indicated that no proper
management systems were implemented by Zimbabwean growers.
A cercosporoid fungus causing a new Fruit and Leaf Spot Disease on Citrus in South
Africa was identified. From morphological and rDNA sequence data (ITS 1, 5.8S and ITS 2),
it was concluded that the new disease was caused by Cercospora penzigii, belonging to the
Cercospora apii species complex. The genera Pseudophaeoramularia and Phaeoramularia
are regarded as synonyms of Pseudocercospora, and subsequently a new combination was
proposed in Pseudocercospora as P. angolensis. Cercospora gigantea was shown to not
represent a species of Cercospora, while Mycosphaerella citri was found to be
morphologically variable, suggesting that it could represent more than one taxon.
A control strategy for the control of FLSD was evaluated in the study. The data showed
that P. angolensis in Zimbabwe can be managed successfully by the removal of all old and neglected orchards, and on timely fungicide applications. Trifloxystrobin + mancozeb +
mineral spray oil (20 g + 200 g + 500 ml/100 l water) applied in November, January and
March was the most effective treatment. Three applications of benomyl + mancozeb +
mineral spray oil (25 g + 200 g + 500 ml/100 l water) applied during the same period, was
the second most effective treatment, and two applications (November and January) of
trifloxystrobin + mineral spray oil (20g + 500 ml/100 l water) and difenoconazole (40 g) per
100 l/water applied twice in November and January, the third most effective treatment.
The spore trap and weather data showed that P. angolensis needs high moisture and
temperatures in excess of 25°C for disease development. It is concluded that P. angolensis in
Zimbabwe can be managed successfully by implementing a holistic approach, which should
be supported by the authorities, organised agriculture and all technical personnel involved in
citrus production. / AFRIKAANSE OPSOMMING: Blaar- en vrugvleksiekte (BVVS) op sitrus, veroorsaak deur Phaeoramularia
angolensis, kom in 18 lande in Afrika voor asook die Comores Eilande in die Indiese Oseaan
en Yemen op die Arabiese skiereiland. Marokko, Suid Afrika, Swaziland en Zimbabwe is
die belangrikste uitvoerders van sitrus in Afrika. Van dié lande het slegs Zimbabwe blaar en
vrugvleksiekte op sitrus. Hierdie siekte is van fitosanitêre en ekonomiese waarde en die
nadelige effek van die siekte, wat slegs kosmetiese van aard is, is venietigend aangesien
vrugte onbemarkbaar is. Totale opbrengsverliese is nie ongewoon in lande soos Kenya nie.
Die doelwitte van die studie was dus om die voorkoms van P. angolensis in Zimbabwe te
bepaal, om die Cercospora Fresen. isolate vanaf Swaziland en Suid-Afrika met mekaar te
vergelyk, om die epidemiologie van die siekte vas te stel en om ‘n effektiewe beheermaatreël
teen die siekte te ondersoek.
Blaarmonsters met kankeragtige letsels wat in die vroeë 1990’s in Zimbabwe gevind
is, het getoon dat die blare geinfekteer is met die swam, Phaeoramularia angolensis.
Ondersoeke is geloots om die verspreiding en intensiteit van BVVS in Zimbabwe en
Mosambiek te bepaal. In Zimbabwe was gevind dat P. angolensis beperk was tot gebiede bo
die 19° Suid breedtegraad, wat die hoër vogtiger gebiede insluit eerder as die droeër,
laagliggende gebiede. Geen P. angolensis simptome kon in Mosambiek gevind word nie.
Tydens die opnames was dit duidelik dat geen geskikte beheerstrategieë toegepas word deur
Zimbabwe se produsente nie.
‘n Nuwe cercosporoid swam, wat blaar en vrugvleksiekte op sitrus is in Suid Afrika
veroorsaak is geidentifiseer. Morfologiese en rDNA volgorde (ITS 1, 5.8S en ITS 2) data het
getoon dat die siekte veroorsaak word deur Cercospora penzigii wat tot die Cercospora apii
spesie kompleks behoort. Die genus Pseudophaeoramularia kan as sinoniem van
Pseudocercospora beskou word en ‘n nuwe kombinasie word voorgestel in
Pseudocercospora as P. angolensis. Cercospora gigantea het getoon dat dit nie ‘n spesie van Cercospora kon verteenwoordig nie terwyl Mycosphaerella citri varieërend voorkom en
meer as een takson kan verteenwoordig.
‘n Beheerstrategie vir die beheer van BVVS is ondersoek. Die data wys dat P. angolensis
in Zimbabwe doeltreffend beheer kan word deur die uitroeiing van ou en verwaarloosde
bome, en deur goed beplande fungisied bespuiting. Trifloxystrobin + mancozeb + minerale
spuitolie (20 g + 200 g + 500 ml/100 l water), wat in November, Januarie en Maart toegedien
is, was die mees effektiefste behandeling. Drie bespuitings van benomyl + mancozeb +
minerale spuitolie (25 g + 200 g + 500 ml/100 l water) wat oor dieselfde tydperk toegedien
is, was die naas beste behandeling. Trifloxystrobin (20 g) + minerale spuitolie (500 ml) per
100 l/water en difenoconazole (40 g) per 100 l/water, beide as twee bespuitings toegedien in
November en Januarie, het die derde beste resultaat opgelewer.
Die spoorlokval en klimatologiese data het getoon dat P. angolensis vogtige toestande en
temperature hoër as 25°C benodig vir siekteontwikkeling. Die afleiding uit die studie is dat
P. angolensis suksesvol beheer kan word indien ‘n holistiese benadering gevolg word en alle
rolspelers naamlik die owerheid, georganiseerde landbou en tegniese personeel die proses
ondersteun.
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Biology, ecology and management of white wax scale, Ceroplastes destructor Newstead (Hemiptera: Coccidae), on citrus and syzygiumWakgari, Waktola (Waktola Muleta) 12 1900 (has links)
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.
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Die insekplaagkompleks op sitrus te VaalhartsMathewson, Johanna 03 1900 (has links)
Thesis (MSc)--Stellenbosch University, 2000. / Full text to be digitised and attached to bibliographic record. / ENGLISH ABSTRACT: The cultivation of citrus in the Vaalharts region is a fairly recent
development. With the introduction of this crop, an insect pest
complex has also developed in this region. The presence of these
pests was studied in eleven orchards, planted with three citrus cultivars
and of varying ages, distributed in the 300 square kilometer cultivation
area. Each orchard was inspected for the presence of pests by making
use of two weekly sampling techniques.
Ten of the most important insect pests of citrus in the Vaalharts
region are briefly described by refering to their general appearance, life
cycles, feeding and pest status and economic threshold. For every
pest various control options, including operational systems, crop
cultivation, biological and chemical control, are discussed and, where
applicable, illustrated by means of graphic presentations. The seasonal
presence of the cirtrus pests in the Vaalharts region is tabulated and
discussed individually. With these details as background, an insect
pest management programme for citrus in the Vaalharts region is
compiled. / AFRIKAANSE OPSOMMING: Die verbouing van sitrus in die Vaalhartsgebied is 'n redelik
onlangse ontwikkeling. Gepaard met die nuwe gewas het daar ook
'n insekplaagkompleks in die gebied ontstaan. Die voorkoms van die
plae is in elt .boorde, beplant met drie sitruskultivars en van
verskillende ouderdomme, verspreid in die 300 vierkante kilometer
verbouingsareaal, bestudeer. Elk van die boorde is weekliks ondersoek
vir die aanwesigheid van plae deur van twee moniteringstegnieke
gebruik te maak.
Die tien belangrikste insekplae van sitrus in die Vaalhartsgebied
word kortliks beskryf deur na hulle algemene voorkoms, lewenssiklus,
voeding en plaagstatus en ekonomiese drempelwaardes asook die
moniteringsmetodes wat gebruik is, te verwys. Vir elke plaag word
beheeropsies, wat operasionele stelsels, gewasverbouing, bloloqlese en
chemiese beheer insluit, bespreek wat, waar toepaslik, aan die hand
van grafiese voorstellings gemustreer word. Die seisoenale
aanwesigheid van die sitrusplae word in 'n tabel aangedui en
individueel bespreek. Met die gegewens as agtergrond is 'n
insekplaagbestuurprogram vir sitrus in die Vaalhartsgebied opgestel.
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