|Wraight, Stephen - Steve|
Submitted to: Biocontrol Science and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/25/2003
Publication Date: 8/1/2004
Citation: Hatting, J.L., Wraight, S.P., Miller, R.M. 2004. Efficacy of beauveria bassiana (hyphomycetes) for control of russian wheat aphid (homoptera: aphidae) on resistant wheat under field condition. Biocontrol Science and Technology. 14:459-473. Interpretive Summary: Populations of the Russian wheat aphid (RWA) have stabilized considerably since the worldwide outbreaks of the past two decades. However, this aphid remains one of the most important pests of dryland cereal crops in many regions. Adaptations by native natural enemies, introduction and establishment of new natural enemies, and development of aphid-resistant grain cultivars have all contributed to improved management of this pest. Resistant wheat varieties limit, but do not eliminate RWA from crops. This provides an excellent opportunity for integration of biological control agents. Fungal pathogens are considered potentially useful components of integrated pest management (IPM) strategies, but little is known with respect to the best ways to apply them in a microbial control context. The principal objective of this study was to determine the optimal timing of spray applications of the common insect pathogenic fungus Beauveria bassiana. Results demonstrated that applications targeting the early flag leaf stage of resistant wheat varieties produced maximum RWA population reductions of 60¿75% relative to untreated controls. The flag leaf is a highly preferred feeding site, and aphids migrate to this leaf from other locations on the plant. It was hypothesized that greater efficacy of the treatments applied during the early flag leaf stage resulted from aphids acquiring lethal doses of fungal spores from the treated foliage and from the generally greater exposure of aphids to the spray applications during this migration. This study indicates that fungal pathogens formulated as sprayable microbial control agents have strong potential to become important components of cereal aphid IPM systems.
Technical Abstract: The microbial control potential of the entomopathogenic fungus Beauveria bassiana was evaluated against Russian wheat aphid (RWA) infesting RWA-resistant wheat cultivars near Bethlehem, Free State Province, South Africa. In small-scale field trials using a back-pack hydraulic sprayer, a single application of fungus at the rate of 5 x 1013 conidia in 350 liters water/ha reduced aphid populations by 60¿75% relative to untreated controls. Maximum efficacy was associated with applications precisely timed to coincide with the initial stages of flag leaf formation. The flag leaf is a highly preferred feeding site, and aphids migrate to this leaf from other locations on the plant. It was hypothesized that greater efficacy of the treatments applied during the early flag leaf stage resulted from aphids acquiring lethal doses of fungal conidia from the treated foliage and from the greater exposure of aphids to spray application during this migration. Fungal efficacy following applications during an earlier growth stage was dependent on wheat cultivar. No significant control was noted on a cultivar (`Elands') expressing high antibiotic resistance, whereas an approximate 50% reduction in aphid numbers was observed on a less resistant cultivar (`Limpopo'). These results also suggested a correlation between fungal efficacy and overall aphid activity (aphid populations were higher, and thus activity greater, on the less resistant cultivar). This study demonstrated potential for integrated use of fungal pathogens and varying levels of host-plant resistance for RWA management.