Submitted to: Proceedings of the Congress of the Entomological Society Of Southern Africa
Publication Type: Abstract Only
Publication Acceptance Date: 5/12/2003
Publication Date: 7/6/2003
Citation: HATTING, J.L., WRAIGHT, S.P., MILLER, R.M. 2003. DEVELOPMENT AND EVALUATION OF A NOVEL BIOASSAY METHOD FOR SCREENING ENTOMOPATHOGENIC HYPHOMYCETES AGAINST CEREAL APHIDS (HEMIPTERA: APHIDIDAE)[ABSTRACT]. PROCEEDINGS OF THE CONGRESS OF THE ENTOMOLOGICAL SOCIETY OF SOUTHERN AFRICA. v. 14. p. 35.
Technical Abstract: Entomopathogenic fungi are the only significant microbial pathogens of the piercing-sucking Homoptera, including aphids. From a commercial point of view, the quantitative expression of the virulence (i.e., median lethal dose or LC50) of these agents is a crucial step in the screening and quality control process during development as mycoinsecticide. A novel bioassay methodology was developed employing live host plants while limiting secondary dose acquisition post inoculation. Initially, four strains of the Hyphomycete Beauveria bassiana (Balsamo) Vuillemin were assayed in a single-dose maximum-challenge test followed by two series of multiple-dose assays; each series comprising five assays. LC50ís, fiducial limits and other regression parameters were used to evaluate the efficacy of the protocol and to investigate between-assay variability. Using this design against the Russian wheat aphid Diuraphis noxia (Kurdjumov), an average LC50 estimate of 85 conidia per mm2 for B. bassiana strain GHA was calculated. The data indicated high assay precision; reflected by an average coefficient of variation for slope of less than 20%, an average chi-squared value of 5.46 ± 2.74 (n = 10 assays), and control mortality below 4%. This design will also accommodate the use of cereal-aphid species other than D. noxia and facilitate tritrophic studies on the effect of host-plant resistance on fungus-induced mortality of aphids. Other measurable phenomena include cadaver distribution (e.g., host plant substrate versus soil surface) as well as pre-mortem behavior of infected aphids.