The levels of de novo DNA methyltransferase were studied during the development of a mealybug, Planococcus lilacinus. No enzyme activity could be detected in extracts from second instar females. But the enzyme occurs at high levels in third instar females and is maintained at that level during fourth instar when gametogenesis, fertilization and chromosome imprinting occur. These results suggest a developmental stage-specific modulation of levels of DNA methyltransferase. Assays with synthetic polymers showed that the enzyme can methylate not only polymers containing GpG but also those containing CpA and CpI.