Thesis (PhD (Agric))--University of Stellenbosch, 2004. / ENGLISH ABSTRACT: Biological control studies were conducted with isolates of entomopathogenic fungi
Beauveria bassiana and Metarrhizium anisopliae from Ethiopia and South Africa against
the spotted stem borer Chilo partellus. The study was conducted from April 2002 to April
2003, at the department of Entomology and Nematology, University of Stellenbosch,
South Africa. The objectives were to screen these isolates for pathogenicity and to
determine the susceptibility of different larval instars; to study the effect of temperature
on fungal development and virulence; to investigate food consumption of fungus treated
larvae; to determine compatibility of fungal isolates with insecticides; to study the effect
of exposure methods and diets on larval mortality; and to evaluate promising isolates
under greenhouse conditions using artificially infested maize plants.
Four isolates of B. bassiana and six isolates of M. anisopliae were tested against
second instar larvae. Of these isolates, B. bassiana (BB-01) and M. anisopliae (PPRC-4,
PPRC-19, PPRC-61 and EE-01) were found to be highly pathogenic inducing 90 to 100
% mortality seven days after treatment. In subsequent assays, the fungal isolates were
tested against third, fourth, fifth and sixth instar larvae. Second and sixth instar larvae
were more susceptible to these isolates than third, fourth and fifth instar larvae.
Conidial germination, radial growth and sporulation of the isolates PPRC-4,
PPRC-19, PPRC-61, EE-01 and BB-01 were retarded at 15 and 35 0C. A suitable
temperature range for the isolates was from 20 - 30 0C. At 25 and 30 0C the isolates
induced 100 % mortality to second instar larvae within four to six days.
Second and third instar C. partellus larvae were treated with the isolates PPRC-4
and BB-01, and daily consumption of maize leaf was measured. Treatment with the fungi
was associated with a reduction in mean daily food consumption.
In in-vitro studies, five concentrations (0.1 ppm, 1 ppm, 5 ppm, 10 ppm, and 100
ppm active ingredients) of the insecticides benfuracarb and endosulfan were tested with
the isolates PPRC-4, PPRC-19, PPRC-16, EE-01 and BB-01. Increasing the
concentration of the insecticides adversely affected germination, radial growth and
sporulation of the isolates. In in-vivo studies combining the fungi, PPRC-4 and BB-01,with low concentrations (1 and 5 ppm a.i.), of the insecticides increased the mortality of
third instar larvae from 65 to 100 %.
Larvae sprayed directly with conidia, exposed to conidia treated leaves and
dipped into conidial suspensions suffered high mortality of 98 to 100 %. Larvae exposed
to treated leaves and larvae sprayed directly with conidia produced high numbers
mycoses in cadavers. Exposure of larvae to treated leaves yielded high sporulation. At a
low conidial concentration (1.25x107 conidia/ml), mycosis and sporulation were high.
The optimum temperature was 20 0C for mycosis and 15 0C for sporulation.
In greenhouse trails, a conidial suspension of 2 x 108 conidia/ml of the
pathogenic isolates was sprayed on 3 to 4 week-old maize plants infested with 20 second
instar larvae per plant. This resulted in suppression of foliar damage. Treatment with the
fungi also reduced stem tunneling and deadheart. In addition, fungal treatment increased
mean plant fresh and dry biomass compared to untreated control plants. In general,
results from laboratory and greenhouse studies indicated that there was good potential for
the use of these fungal isolates for controlling C. partellus larvae. / AFRIKAANSE OPSOMMING: Biologiese beheerstudies is uitgevoer met isolate van die insekpatogeniese swamme,
Beauvaria bassiana en Metarrhizium anisopliae teen die gespikkelde stamboorder, Chilo
partellus. Die doelwitte was om hierdie isolate te evalueer vir patogenesiteit; die
vatbaarheid van verskillende larvale instars teenoor hulle te bepaal; die invloed van
temperatuur op swamontwikkeling en virulensie te bepaal; die voedsel inname van
swambehandelde larwes te ondersoek; die verenigbaarheid van die swamisolate met
insektedoders te bepaal; die invloed van blootstellingsmetodes en diëte op larvale
mortaliteit; en om belowende isolate in glashuisproewe te evalueer met gebruik van
kunsmatig besmette mielieplante.
Vier isolate van B. bassiana en ses isolate van M. anisopliae is teen tweede instar
larwes getoets. Uit dié isolate is B. bassiana (BB-01) en M. anisopliae (PPRC-4, PPRC-
19, PPRC-16 en EE-01) as hoogs patogenies bevind. Hulle het 90 tot 100 % mortaliteit
na sewe dae veroorsaak. In daaropvolgende essays, is die swamisolate teen derde, vierde,
vyfde en sesde instar larwes getoets. Tweede en sesde instar larwes was gevoeliger vir
die isolate as die derde, vierde en vyfde instar larwes.
Spoorkeming, radiale groei en sporulasie van die isolate PPRC-4, PPRC-19,
PPRC-61, EE-01 en BB-01, is by 15 en 35 0C vertraag. ‘n Aanvaarbare temperatuurreeks
vir die isolate is vanaf 20 tot 30 0C. By 25 en 30 0C het die isolate 100 % mortaliteit teen
tweede instar larwes binne vier tot ses dae geïndusseer.
Tweede en derde instar C. partellus larwes is met die isolate PPRC-4 en BB-01
behandel en die daaglikse inname van mielieblare gemeet. Behandeling met die swamme
is met ‘n afname in die gemiddelde voedselinname geassosieer
In in-vitro studies is vyf konsentrasies (0.1 dpm, 1 dpm, 5 dpm, 10 dpm en 100
dpm aktiewe bestandele) van die insekdoders, benfuracarb en endosulfan getoets saam
met die isolate PPRC-4, PPRC-19, PPRC-16, EE-01 en BB-01. ‘n Toename in die
konsentrasie van die insekdoders het ontkieming, radiale groei en sporulasie van die
isolate benadeel. In in-vitro studies het die kombinering van die die swamme, PPRC-4 en
BB-01, met lae konsentrasies (1 en 5 dpm a.b.) van die insekdoders mortaliteit van derde
instar larwes vanaf 65 tot 100 % laat toeneem.
Larwes wat direk met spore gespuit is, aan behandelde blare blootgestel is en in
spoorsuspensies gedoop is het tot hoë mortaliteit gelei, (98 tot 100 %). Blootstelling aan
behandelde blare saam met ‘n lae konidiakonsentrasie, 1.25x106 spore/ml) en ‘n
temperatuur van 15 tot 20 0C het tot hoë swammikose en sporulasie in kadawers gelei.
In glashuisproewe, is ‘n spoorsuspensies van 2 x 108 spores/ml van die
patogeniese isolate op 3 tot 4 weekoud mielieplante wat met 20 tweede instar larwes per
plant besmet is gespuit. Dit het blaarskade onderdruk. Behandeling met die swamme het
ook stamtonnels en dooiehart verminder. Boonop het swambehandeling die vars- en droë
plantbiomassa laat toeneem in vergelyking met die onbehandelde kontrole plante. Oor die
algemeen het resultate van laboratorium- en glashuisproewe getoon dat daar goeie
potensiaal is vir die gebruik van hierdie swamisolate vir die beheer van C. partellus
larwes.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/16063 |
| Date | 11 August 2011 |
| Creators | Mekonnen, Tadele Tefera, Tadele Tefera |
| Contributors | Pringle, K.L., University of Stellenbosch. Faculty of Agrisciences. Dept. of Forest and Wood Science. |
| Publisher | Stellenbosch : University of Stellenbosch |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | English |
| Type | Thesis |
| Format | 127 leaves : ill. |
| Rights | University of Stellenbosch |
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