In vitro experiments using [1-(14)C] and [2-(14)C]acetate were devised to study the
biosynthesis of the defensive coccinellid alkaloids adaline and coccinelline in Adalia
2-punctata and Coccinella 7-punctata, respectively. The labelled alkaloids obtained
in these experiments had a specific activity about ten times higher than that of the
samples obtained in feeding experiments. This in vitro assay has enabled us to demonstrate
that these two alkaloids are most likely biosynthesised through a fatty acid rather
than a polyketide pathway, that glutamine is the preferred source of the nitrogen
atom and that alkaloid biosynthesis takes place in the insect fat body.