Responses of the ticks Amblyomma hebraeum and A. variegatum to known or potential components of the aggregation-attachment pheromone. III. Aggregation.

Ten known or potential components of the aggregation-attachment pheromone (AAP) of the ticks Amblyomma hebraeum and A. variegatum, as well as mixtures of these components, extracts of prefed males and live prefed males, were tested as aggregation stimulants. In field assays, laboratory-reared unfed male and female ticks were released 20 cm downwind of CO2/pheromone release sites; the numbers of ticks that aggregated at the release sites were recorded after 30 min. In A. variegatum, aggregation was induced by methyl salicylate, o-nitrophenol, 2,6-dichlorophenol, phenylacetaldehyde and some mixtures containing these compounds; a strong aggregation response was induced by an extract of five prefed males A. variegatum and a weak response was induced by an extract of 50 prefed males of A. hebraeum. In A. hebraeum, aggregation was induced by phenylacetaldehyde, mixtures of compounds that included phenylacetaldehyde, extracts of 50 prefed males of A. hebraeum or A. variegatum and 50 live prefed males of A. hebraeum. In A. variegatum, aggregation was inhibited if compounds that do not occur naturally in the AAP of the species were included in mixtures. In A. hebraeum, phenylacetaldehyde appeared to act as an arrestant for ticks that had been attracted to release sites by other compounds.