Defensive potential of components of the larval osmeterial secretion of papilionid butterflies against ants

ABSTRACT. Toxicity and repellency of components of larval osmeterial secretions of the Papilionidae to the ants Lasius niger and Crematogaster matsumurai were evaluated in the laboratory and in the field. The test chemicals comprised five aliphatic acids, five esters, three monoterpene hydrocarbons and four sesquiterpenes.
The majority of aliphatic acids and esters exhibited weak to potent toxicity, but exposure to acetic, isobutyric, 2-methylbutyric and isovaleric acids, ethyl 2-methylbutyrate and methyl 3-hydroxy- n -butyrate proved fatal to both ant species. Monoterpene hydrocarbons also had considerable toxicity, whereas sesquiterpenes were only slightly or not toxic. Of the terpenic compounds tested, α-pinene was found to be the most toxic. L. niger ejected formic acid in response to d -limonene.
Field experiments revealed that all the compounds examined except 3-hydroxy- n -butyric acid were significantly repellent to worker ants of both species. Acetic, isobutyric and 2-methylbutyric acids especially showed pronounced repellency, while the esters were less deterrent.
Among terpenic compounds, the repellency of caryophyllene oxide was noticeable. d -Limonene elicited no particular response, other than rapid evasion, by L. niger.