Control of the woolly apple aphid, Eriosoma lanigerum (Hausmann) (Hemiptera: Aphididae), using entomopathogenic fungi

Mathulwe, Letodi Luki (2019-04)

Thesis (MScConsEcol)--Stellenbosch University, 2019.

Thesis

ENGLISH ABSTRACT: Eriosoma lanigerum (Hausmann) (Hemiptera: Aphididae), or woolly apple aphid (WAA), is a serious pest of apple trees (Malus domestica Borkhausen), attacking both the root system and the arboreal parts of the tree. Current management of WAA in apple orchards relies on the use of both biological and chemical control. However, biological control using the principal parasitoid of the WAA, Aphelinus mali (Heldemann) (Hymenoptera: Aphelinidae), was found to be ineffective. The use of chemical control has also proven to be negative, as biotypes of the WAA have developed resistance to the chemicals used. The use of entomopathogenic fungi (EPF) has been identified as promising biological control method against a wide array of insect pests. The main aim of the current study was to conduct a survey of EPF in the local apple orchards of the Western Cape province, and to screen their ability to control the root colonies of the WAA, under optimum laboratory conditions. The above was achieved by collection of soil and WAA-infested root samples from six apple farms. The EPF were baited from collected soil samples, using susceptible insect hosts, and directly from WAA females collected from the infested root samples. Successfully isolated fungi were grown on agar plates and screened for their pathogenicity against insects. The isolated EPF were identified both morphologically and molecularly, which include Beauveria bassiana, Isaria fumosorosea, Metarhizium brunneum, Metarhizium pinghaense, Metarhizium robertsii and Purpureocillium lilacinum. The second aim of the study was to screen the six isolated EPF for their virulence against the WAA under optimum laboratory conditions. The above was achieved by conducting screening, concentration-dose-response and exposure-time-response bioassays. Metarhizium pinghaense and M. brunneum proved to be the most effective species against the root colonies of WAA, indicating that the local isolates of EPF have potential for the biological control of the WAA. The final aim of the current study was to test for the persistence of M. pinghaense and M. brunneum on apple bark over a period of 3 weeks under laboratory conditions, and to determine whether the fungal conidia would attach to crawlers, or the fourth-stage nymphs, of the WAA as they move up tree trunks from the roots to the aerial parts of the apple trees. The above was done by means of spraying apple bark with a standard conidial concentration of 1.0 x 107 conidia/ml of both M. pinghaense and M. brunneum, respectively. The persistence of fungal conidia on the apple bark was measured using codling moth larvae as an indicator. The results indicated M. pinghaense to have better persistence on the apple bark over a period of 3 weeks than did M. brunneum. Further analysis of persistence, whereby the root colonies of the WAA were exposed to the dried conidia of M. pinghaense on apple bark, showed that M. pinghaense was capable of inducing mortality of about 39-82% in colonies of WAA under optimum laboratory conditions, when exposed for a period of 10 days. The current study has highlighted both the diversity of soilborne EPF in the local apple orchards of the Western Cape, and their potential to be successfully integrated in managing the presence of the WAA colonies in apple orchards. The local isolate of M. pinghaense has shown to be the best candidate for managing WAA. Therefore, future research should focus on testing the efficacy of the local isolate of M. pinghaense against the WAA, under both glasshouse and field conditions.

AFRIKAANSE OPSOMMING: Eriosoma lanigerum (Hausmann) (Hemiptera: Aphididae), ook bekend as die appelbloedluis (WAA), is ʼn ernstige pes van appelbome (Malus domestica Borkhausen) wat skade veroorsaak aan die wortelstelsel, takke en blare. Die luis word tans bestuur in appelboorde deur die gebruik van chemiese en biologiese beheermiddels. Biologiese beheer deur die gebruik van die hoofparasiet van die WAA, Aphelinus mali (Heldemann) (Hymenoptera: Aphelinidae), is egter getoets en daar was gevind dat dit oneffektief is in die beheer van die luis. Daar was ook bewys dat die gebruik van chemiese middels oneffektief is, aangesien sommige biotipes van WAA weerstand ontwikkel het teen die chemikalieë wat gebruik word. Die gebruik van entomopatogeniese swamme (EPF) is geïdentifiseer as ʼn belowende, effektiewe metode vir die beheer van verskeie insek peste. Die huidige studie was gefokus daarop om ʼn opname te doen van EPF in die plaaslike appelboorde van die Wes-Kaap provinsie en dan te toets of hul die vermoë het om wortel kolonies van WAA te beheer in optimale laboratorium omstandighede. Om dit te toets, was grond en wortels wat geïnfekteer was met WAA, versamel van ses appelplase. Die EPF was toe geïsoleer van die grondmonsters deur vatbare insekte te gebruik as lokinsekte. EPF is ook geïsoleer van die wortels deur WAA wyfies te versamel vanaf die geïnfekteerde wortelmonsters. Swamme wat suksesvol geïsoleer is, is dan gegroei op agarplate, waarna hul vermoë om insek peste te beheer getoets is. Die EPF wat geïsoleer is, is geïdentifiseer deur morfologiese en molekulêre tegnieke en sluit in Beauveria bassiana, Isaria fumosorosea, Metarhizium brunneum, Metarhizium pinghaense, Metarhizium robertsii en Purpureocillium lilacinum. Die tweede doelwit van die studie was om die effektiwiteit van die ses geïsoleerde EPF te toets op appelbloedluise in optimale laboratorium omstandighede. Om dit te toets was die EPF aangewend teen verskillende konsentrasies en die appelbloedluise blootgestel aan die swamme vir verskillende tydperke. Die twee EPS spesies, Metarhizium pinghaense en M. brunneum was mees effektief teen die wortel kolonies van ABL, wat beteken dat die plaaslike EPS isolate potensiaal het vir die beheer van die ABL. Die derde doelwit van die studie was om te toets of M. pinghaense en M. brunneum kan oorleef op appelboombas vir ʼn periode van drie weke in optimale laboratorium omstandighede, asook om vas te stel of die swamme se spore kan vassit aan die kruipers of die vierde stadium nimfe soos wat hul op beweeg teen die boomstam vanaf die wortels na die takke. Om bogenoemde te toets, was appelboom bas gespuit deur gebruik te maak van ʼn standaard spoor konsentrasie van 1.0 x 107 spore/ml van M. pinghaense of M. brunneum. Die oorlewing van die swam spore op die bas was getoets deur kodlingmot larwes te gebruik as indikatore. Die resultate het getoon dat M. pinghaense langer infektief gebly het op die bas as M. brunneum, oor ʼn tydperk van 3 weke. Verdere analises is uitgevoer waar die wortel kolonies van die WAA blootgestel is aan die gedroogde spore van M. pinghaense op appel bas en het getoon dat M. pinghaense in staat was om sterftesyfers van 39-82% te veroorsaak in WAA kolonies, na blootstelling vir 10 dae, in optimale laboratorium omstandighede. Die huidige studie beklemtoon die diversiteit van EPF in die plaaslike appelboorde van die Wes-Kaap, asook hul potensiaal om suksesvol geïntegreer te word in die bestuur van WAA getalle in appelboorde. Die studie het getoon dat die plaaslike isolaat, M. pinghaense, die beste kandidaat is uit die wat getoets is, vir die beheer van WAA. Toekomstige navorsing moet dus fokus daarop om die effektiwiteit te toets van M. pinghaense teen WAA in beide glashuis- en veld omstandighede.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/106136
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