Purification and characterisation of proteins secreted by the entomopathogenic fungus Metarhizium anisopliae with insecticidal activity against adults of the Mediterranean fruit fly, Ceratitis capitata (Diptera: Tephritidae)

BACKGROUND: The control of the Mediterranean fruit fly (medfly) Ceratitis capitata (Wied) is usually performed with protein bait sprays incorporating chemical insecticides that may have adverse effects on humans, non-target organisms and the environment. In recent years, scientists have sought more environmentally friendly insecticides for medfly control, such as plant- and microorganism-derived compounds. Among these compounds, entomopathogenic fungi are an unexplored source of natural insecticides.RESULTS: The crude soluble protein extract (CSPE) of the entomopathogenic fungus Metarhizium anisopliae (Mestch.) (strain EAMa 01/58-Su) shows chronic insecticidal activity when administered per os. Mortality in flies exhibits a dose response. The CSPE produces an antifeedant effect in adult flies, a result probably due to a progressive deterioration of the fly midgut after ingestion of the extract. Protease and temperature treatments show that insecticidal activity against C. capitata is due to proteinaceous compounds that are highly thermostable. Four monomeric proteins from this crude extract have been purified by liquid chromatography and gel electroelution. Although all four monomers seem to be involved in the insecticidal activity of the CSPE, the 15 kDa and the 11 kDa proteins appear to be mainly responsible for the observed insecticidal effect.CONCLUSIONS: Four new fungal proteins with insecticidal activity have been purified and identified. These proteins might be combined with insect baits for C. capitata biocontrol.