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

Abstract.

• 1 Field experiments demonstrated that the faecal covering that female Microrhopala vittata (Fabr.) (Coleoptera: Chrysomelidae) place over their egg masses significantly reduces egg mortality.
• 2 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.
• 3 The parasite Chrysonotomyia sp. (Hymenoptera: Eulophidae) generally parasitizes only the bottom egg in the egg mass, while predators rarely penetrate the faecal covering.
• 4 No significant relationship was found between mortality and the number of egg masses per leaf.
• 5 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.