Dissertation (PhD (Agric))--University of Stellenbosch, 2000. / ENGLISH ABSTRACT: A study was made of the basic biology of subterranean Eriosoma
lanigerum (Hausmann) populations in apple orchards in the Western Cape
Province of South Africa.
The absence of cornicles and the presence of a vulva could be used to
identify 1st instar nymphs and adults respectively. Body length, body width and
length of the hind femur are useful for separating 2nd
, 3rd and 4th instars.
However, separation of 2nd from 3rd instar nymphs was very unreliable.
Maximum population growth rate was at 23°C while at 30 °C
population growth was zero. The estimated minimum and maximum threshold
temperatures for development were 4.32 and more than 30°C respectively.
Numbers of underground E. lanigerum in soil samples taken using
mechanical and hand augers were similar. However, numbers of aphids in
samples were influenced by the distance from the trunk at which the samples
were taken and the presence and the type of root material in the samples.
More aphids were recorded close to the trunk, and at a given distance from
the trunk more aphids were recorded if there was root material in the sample,
especially if the roots were galled. early autumn (February, March) and declined during winter, especially if the
winter rainfall was high. These cycles coincided with the nitrogen cycles in the
roots.
Embryos were also present in all instars throughout the year. There
were more embryos in the 4th instar and adult aphids than in the other instars.
The highest number of embryos in the 4th instar and adult aphids occurred
during spring, which coincided with peak nitrogen levels in the roots of apple
trees. Nitrogen levels in root material adjacent to galls and in ungalled roots
were higher than in root galls.
A number of entomopathogenic fungi, including species of
Conidiobolus, Hirsufella and Beauveria were found. Their present contribution
to biological control is not known.
A straw mulch suppressed subterranean E. lanigerum population levels
at least as well as the soil insecticide, imidacloprid, currently in use. / AFRIKAANSE OPSOMMING: 'n Studie van die basiese biologie van ondergrondse bevolkings van
, Eriosoma lanigerum (Hausmann) is in appelboorde in die Weskaap Provinsie
van Suid-Afrika uitgevoer.
Die afwesigheid van kornikels en die aanwesigheid van 'n vulva kon
gebruik word om die 1ste instar nimfe en volwassennes onderskeidelik te
identifiseer. Liggaamslengte, liggaamsbreedte en die lengte van die agterste
femur kon gebruik word om die 2de
, 3de en 4de instars van mekaar te
onderskei. Onderskeiding tussen 2de en 3de instar nimfe was egter baie
onbetroubaar.
Maksimum bevolkingsgroei het by 23°C plaasgevind, terwyl dit nul was
by 30 °C. Die beraamde minimum en maksimum temperature vir ontwikkeling
was by 4.32 en meer as 30°C onderskeidelik.
Getalle van ondergrondse E. lanigerum in grondmonsters wat geneem
is met gebruik van meganiese en hand bore was eenders. Getalle plantluise in
monsters is egter beïnvloed deur die afstand vanaf die stam waarby die
monsters geneem is en die teenwoordigheid van wortelmateriaal in die
monsters. Meer plantluise is aangeteken as daar wortelmateriaal in die
monsters was, en veral as daar galle op die wortels was. Die appelbloedluis was dwarsdeur die jaar ondergronds aktief.
Bevolkingsvlakke het gedurende die vroeë somer (November, Desember) en
vroeë herfs (Februarie, Maart) toegeneem, en gedurende die winter
afgeneem, veral as die winterreënval hoogwas.
Embrio's was ook teenwoordig dwarsdeur die jaar. Daar was meer
embrio's in die 4de instar en volwasse plantluise as in die ander instars. Die
hoogste aantal embrio's in die 4de instar en volwasse plantluise het in die lente
voorgekom, wat saamgeval het met piek stikstofvlakke in die wortels van
appelbome. Stikstofvlakke in wortelmateriaal aangrensend aan wortels en in
wortels sonder galle was hoër as in wortelgalle.
Talle entomopatogeniese swamme, insluitend spesies van
Conidiobolus, Hirsufella en Beauvaria IS gevind. Hulle huidige bydrae tot
biologiese beheer is nie bekend nie.
'n Strooideklaag het ondergrondse bevolkingsvlakke van E. lanigerum
tot ten minste dieselfde mate as die grondinsektedoder, imidacloprid, wat tans
in gebruik is, onderdruk.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/51638 |
| Date | 03 1900 |
| Creators | Damavandian, M. R. |
| Contributors | Pringle, K. L., 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 | xii, 126 p. : ill. |
| Rights | Stellenbosch University |
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