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

[摘要] 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.

[发布机构] Stellenbosch University