Two forms of egg defence in a chrysomelid beetle: egg clumping and excrement cover

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Abstract
Field experiments demonstrated that the faecal covering that female Microrhopala vittata (Fabr.) (Coleoptera: Chrysomelidae) place over their egg masses significantly reduces egg mortality. The bottom egg in the egg mass, which lies against the leaf of the host plant, suffers significantly higher mortality than the other eggs in the egg mass. The parasite Chrysonotomyia sp. (Hymenoptera: Eulophidae) generally parasitizes only the bottom egg in the egg mass, while predators rarely penetrate the faecal covering. No significant relationship was found between mortality and the number of egg masses per leaf. By placing eggs in masses, females may ensure that at least the upper eggs in any egg mass are effectively protected against virtually all natural enemies likely to pose a threat.