ABSTRACT. The parasitoid, Bracon mellitor, will probe with its ovipositor plant structures containing its host. The identification of methyl parahydroxy‐benzoate (methyl parasept), an antimicrobial additive to the semi‐synthetic diet used for rearing the host, as a releaser of this behaviour prompted an investigation of the parasitoid's response to this chemical. Its absence from field hosts suggested the response was learned. Female parasitoids reared in host‐infested cotton plant buds from the fields or in methyl parasept‐free hosts did not respond to methyl parasept alone until exposed to hosts contaminated with it. This is taken to imply associative learning by the females reared from the methyl parasept‐free hosts. A few responses to methyl parasept were elicited from inexperienced females reared from methyl parasept‐contaminated hosts, but their responsiveness increased after they had been exposed to methyl parasept‐contaminated hosts as oviposition stimuli. These results point to the caution that must be exercised in the isolation and identification of kairomones.

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