Defensive Secretions

A small number of beetles of the genus Paederus when disturbed or crushed exude some haemolymph containing pederine (Figure 4.18) which produces severe blisters. The beetles are hence known as blister beetles. Although the biosynthetic origin may not be very obvious, some early studies showed the incorporation of acetate and propionate, suggesting a polyketide origin. The biosynthetic scheme requires several subsequent methylations on carbon and oxygen (Figure 4.18). Recent work

pederine

Figure 4.18 The probable biosynthetic precursors in the formation of the defensive compound pederine. The figure summarizes the suggestions of the investigators based on the radio-labelling of the compound and some degradation products pederine

Figure 4.18 The probable biosynthetic precursors in the formation of the defensive compound pederine. The figure summarizes the suggestions of the investigators based on the radio-labelling of the compound and some degradation products has shown that pederine is actually produced by Pseudomonas species bacteria which are symbionts (symbiotic micro-organisms) inside the beetles, and it is only produced by females, who pass it to their eggs. Pederine and related compounds have also been found in marine organisms.

The coccinellines from ladybirds (Chapter 3), were first thought to be of polyketide origin when it was shown that the beetles incorporated [l-14C]acetate and [2-14C]acetate, but subsequently a fatty acid origin has been demonstrated (Figure 3.26).

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