Is esterase-P encoded by a cryptic pseudogene in Drosophila melanogaster?

We have amplified and sequenced the gene encoding Esterase-P (Est-P) in 10 strains of Drosophila melanogaster. Three premature termination codons occur in the coding region of the gene in two strains. This observation, together with other indirect evidence, leads us to propose that Est-P may be a pseudogene in D. melanogaster. Est-P would be a "cryptic" pseudogene, in the sense that it retains intact the coding sequence (without stop codons and other alterations usually observed in pseudogenes) in most D. melanogaster strains. We conjecture that the beta-esterase cluster may consist in other Drosophila species of functional and nonfunctional genes. We also conjecture that the rarity of detected pseudogenes in Drosophila may be due to the difficulty of discovering them, because most of them are cryptic.