IDENTIFICATION OF ELECTROPHYSIOLOGICALLY-ACTIVE COMPOUNDS FOR NEW-WORLD SCREWWORM, COCHLIOMYIA-HOMINIVORAX, IN LARVAL WOUND FLUID

Acidic and non-acidic fractions from extracts of fluid from sheep woun ds infested with larvae of Cochliomyia hominivorax (Coquerel) were ana lysed by linked gas chromatography and electroantennography in order t o detect electrophysiologically-active compounds that could be potenti al attractants. Responses to twenty-six electrophysiologically-active compounds were observed and, on the basis of electron impact and chemi cal ionization mass spectrometry and co-chromatography with authentic compounds, twenty-five of these compounds were characterized. The most abundant compounds identified in the larval wound fluid were straight and methyl-branched aliphatic carboxylic acids, ranging from C2- to C 5-carbon chain length. Butanoic acid, for example, was found to be pre sent at approximately 0.45 mg/ml. Aliphatic carboxylic acids with long er chain lengths were also observed but in trace amounts. Three aromat ic carboxylic acids, benzoic, phenylethanoic and 3-phenylpropanoic aci ds were also present but only phenylethanoic and 3-phenylpropanoic aci ds elicited electroantennographic responses. Phenol and indole were by far the most abundant components of the non-acid fraction of the larv al wound fluid with all other components, except delta-valerolactam, p resent at levels of less than 5% that of phenol which was present at a concentration of 0.05 mg/ml. Electroantennographic studies of straigh t-chain aliphatic carboxylic acids showed that pentanoic acid elicited the strongest response from C.hominivorax. Similar studies showed tha t 1-octen-3-ol elicited stronger responses than 3-methylphenol, indole , phenol or dimethyldisulphide. 3-Methylindole, which was not found in the wound fluid, also elicited a strong response. The potential behav ioural significance of these compounds is discussed in relation to tha t of known attractants of C.hominivorax and other dipteran pests of ma mmals.