Genetics and Expression of Mottled Body: Mosaic Mutant of the German Cockroach (Dictyoptera: Blattellidae) with Possible Cytoplasmic Inheritance

Abstract

Mottled body (Mt) is a mutant of the German cockroach, Blattella germanica (L.), which is characterized by extensive color variegation on the surface of the body. Irregular light patches appear in the integument of wild-type black color. Mottling is more conspicuous on abdominal segments than on thoracic segments. The character is clearly observed in the nymphal stage but also can be seen on the small dorsal tergites of adults. Expression of mottling is variable. The trait is mostly maternally inherited, and cytoplasmic factor(s) may be involved. A method for judging the degree of mottling was established. Degree of mottling was scored on the surfaces from 1st to 3rd thoracic and 1st to 7th abdominal segments. Mottling patterns did not change during late nymphal development. Mottling expression did not decrease from the Mt stock to the F1 (Mt female × wild-type male), and F2 (F1Mt female × wild-type male). Mottling patterns were often different between left and right sides. Patterns were often discontinuous across the median line of the body and sometimes one side was mottled and the other side almost wild-type color. Separate scoring between left and right surfaces and also between dorsal and ventral surfaces revealed that the degree of mottling was more correlated dorsoventrally than laterally. This suggests that mottling patterns were determined before dorsal closure during embryogenesis and are influenced by the shape peculiar to cockroach embryos packed in the ootheca, which is broad dorsoventrally and compressed laterally.