Parnassius apollo (Lepidoptera: Papilionidae) is a butterfly species which was common in Europe in 19th century,
but now it is considered as near threatened. Various programs devoted to protect and save P. apollo have been
established, between others the one in Pieniny National Park (Poland). An isolated population of this butterfly
has been restored there from a small group of 20–30 individuals in early 1990s. However, deformations or reductions
of wings occur in this population in a relatively large number of insects, and the cause of this phenomenon is
not known. In this report, the occurrence of lesions in the wingless (wg) gene is demonstrated in most of tested
butterflies with deformed or reduced wings, but not in normal insects. Although the analyses indicated that wg
lesion(s) cannot be the sole cause of the deformed or reduced wings in the population of P. apollo from Pieniny,
the discovery that this genetic defect occurs in most of malformed individuals, can be considered as an important
step in understanding this phenomenon.