Dissertation (PhD)--University of Stellenbosch, 2001. / ENGLISH ABSTRACT: The basic biology of Eriosoma lanigerum (Hausmann) and its natural enemy,
Aphelinus mali (Haldeman), was investigated in the Western Cape Province of South
Africa.
The first instar nymph can be identified by the absence of cornicles and the
adult female by the presence of the vulva. Body length and distance between cornicles
can be used to distinguish between the 2nd
, 3rd and 4th instars.
The development of E. lanigerum was negatively influenced by temperatures
above 27DC. The net replacement rate (Ro) and intrinsic rate of increase (rm) peaked at
20DC. The theoretical lower and upper threshold temperatures for development were
estimated at 4.48DC and 28.07DC, respectively.
Crawlers of E. lanigerum migrated from the roots up into the trees during
spnng to start new infestations. Colonies became visible from December and
maximum colony numbers were reached from the end of summer until autumn, at
which time most of the colonies were parasitised by A. mali. Colony numbers
declined at the end of autumn after high parasitism and the appearance of winged E.
lanigerum. The aphid overwintered on the tree. Chemical sprays, rain during spring
and high temperature influenced population numbers negatively.
E. lanigerum can be monitored by counting the unparasitised colonies in leaf
axils of half of each of 25 trees per 2 hectare plot with 5 unparasitised colonies as the
economic threshold. Sampling error was high at 40% but increasing the number of
trees did not reduce it. Presence-absence sampling, which will reduce the time
required for monitoring, did not seriously compromise the reliability of decisions
regarding the necessity for intervention. Chemicals containing nitrogen usually sprayed for bitterpit control stimulated
the settling of E. lanigerum crawlers on Granny Smith trees, while fruit weevil
barriers for the control of Phlyctinus callos us Boh. limited crawler movement into the
trees but did not prevent colonisation.
All the postembryonic developmental stages of E. lanigerum were parasitised
by A. mali. Complete parasitism of the population was never reached as younger
instars sheltered under other aphids and mummified aphids.
Development of A. mali was not influenced negatively by high temperatures.
The minimum developmental temperature and number of degree days needed for
development of the larval stage and emergence of the adult from the mummy were
.6.72°C and 172.41°D, and 10.27°C and 109.89°D respectively. Mummies collected
during early winter survived long periods of cold storage in postdiapause. The
rrummum threshold temperature for postdiapause development of A. mali was
·10.15°C.
Most chemicals tested against A. mali adults were highly toxic to the wasp,
except endosulfan and two growth regulators, flufenoxuron and fenoxycarb. The
mortality of adults exposed to the fungicides tested was low within the first 24 hours.
The percentage emergence from the mummies was high for all chemicals tested, but
more than 60% of the adults died soon after emergence from mummies treated with
chlorpyrifos. Nearly 30% of the adults died soon after they emerged from carbaryl
(XLR-Plus) and fenthion treated mummies. The growth regulators, flufenoxuron and
fenoxycarb, did not influence fecundity adversely. / AFRIKAANSE OPSOMMING: Die basiese biologie van Enosoma lanigerum (Hausmann) en sy natuurlike
vyand, Aphelinus mali (Haldeman), in die Weskaap Provinsie van Suid-Afrika
isondersoek.
Die eerste instar nimf kan aan die afwesigheid van kornikels en die
volwassenes aan die teenwoordigheid van die vulva uitgeken word. Die
liggaamslengte en afstand tussen die kornikels kan gebruik word om tussen instar 2, 3
en 4 te onderskei.
Die ontwikkeling van E. lanigerum word nadelig deur temperature bo 27°C
beïnvloed. Die netto vervangingstempo (Ro) en intrinsieke tempo van toename (rm)
was die hoogste by 20°C. Die teoretiese minimum en maksimum temperatuur
drempelwaardes vir ontwikkeling was 4.48°C en 28.07°C onderskeidelik.
In die lente beweeg E. lanigerum kruipers op vanaf die wortels tot in die bome
om nuwe kolonies te begin. Kolonies is sigbaar vanaf Desember en die hoogste
koloniegetalle word aan die einde van die somer tot die herfs bereik, wanneer die
meeste van die kolonies dan ook deur A. mali geparasiteer word. Teen laat-herfs neem
koloniegetalle af as gevolg van hoë parasitisme en die verskyning van gevleuelde E.
,lanigerum. E. lanigerum oorwinter op die appelboom. Chemiese behandelings, reën
gedurende die lente en hoë temperatuur beïnvloed koloniegetalle nadelig.
E. lanigerum kan deur die aantal ongeparasiteerde kolonies in die blaaroksels
van die helfte van 25 bome per 2 hektaar blok te tel, met 5 ongeparasiteerde kolonies
as die ekonomiese drempelwaarde, gemonitor word. Die steekproefnemingsfout was
hoog (40%), maar kon nie verminder word deur die aantal bome wat gemonitor is te
verhoog nie. Steekproefneming, vir aan- of afwesigheid van kolonies, wat monitortyd sal verminder, het min invloed op die betroubaarheid van besluitnemings oor die
noodsaaklikheid van bespuitings gehad.
Stikstofbevattende chemikalieë, wat vir die beheer van bitterpit gespuit word,
stimuleer vestiging van E. lanigerum kruipers op Granny Smith bome, terwyl
snuitkewerversperrings, vir die beheer van Phlyctinus callosus Boh., die opwaartse
beweging van kruipers in die bome beperk, maar nie kolonievorming van E.
lanigerum verhoed nie.
Alle postembrioniese ontwikkelingstadiums van E. lanigerum is deur A. mali
geparasiteer. Totale parasitisme is nooit bereik nie, omdat jonger instars onder ander
bloedluise en gemummifiseerde bloedluise skuil.
Die ontwikkeling van A. mali word nie deur hoë temperature benadeel nie. Die
minimum ontwikkelingstemperatuur en graaddae, nodig vir ontwikkeling van die
larwale stadium en die verskyning van die volwassene uit die mummie, was 6.72°C
met 172.4loD en 10.27°C met 109.89°D, onderskeidelik. Mummies wat vroeg in die
winter versamel is, het lang periodes van koelopberging oorleef. Die minimum
temperatuur drempelwaarde vir A. mali ontwikkeling in postdiapouse was 10.15°C.
Die meeste van die chemikalieë wat getoets is, was hoogs toksies vir die
volwasse wesp, behalwe endosulfan en die twee groeireguleerders, flufenoxuron en
fenoxycarb. Die mortaliteit van volwassenes wat aan swamdoders blootgestel is, was
laag binne die eerste 24 uur na blootstelling. Die persentasie uitkoms vanuit mummies
was hoog vir al die chemikalieë wat getoets is, maar met chlorpyrifos het 60% van die
volwassenes net na uitkoms doodgegaan. Ongeveer 30% van die volwassenes is dood
na verskyning vanuit mummies wat met carbaryl (XLR-Plus) en fenthion gespuit is.
Die groeireguleerders, flufenoxuron en fenoxycarb, het nie die vrugbaarheid van die
parasiet merkbaar beïnvloed nie.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/52491 |
| Date | 03 1900 |
| Creators | Heunis, J. M. (Juanita Maria) |
| 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 | xv, 238 p. : ill. |
| Rights | Stellenbosch University |
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