Acta Scientiarum Polonorum
Silvarum Colendarum Ratio et Industria Lignaria

Introduction: Small balsam (Impatiens parviflora) is considered in Poland a highly expansive and dangerous species of significant importance (invasiveness category 4). It came from Asia as an ornamental plant, and over time made its way into forest ecosystems. Right now it has spread throughout the country. It changes the species composition of the undergrowth, and at strong lighting conditions it displaces the native species Impatiens noli-tangere. Siobla sturmii is a sawfly (Tenthredinidae, Sioblinae), which is one of the few phytophages feeding on representatives of the Impatiens spp. family in Europe and Asia. In Poland it is known from a small number of sites, located mainly in the southern part of the country, where it was found on its main European host – Impatiens noli-tangere. In the literature this insect is described as a monophagous species, whose larvae inhabit and feed on the green parts of I. noli-tangere. In Europe the presence of S. sturmii on the surface of I. parviflora has been described only once in Europe; however, the potential completion of the full development cycle of this insect outside of the I. noli-tangere tissues is considered disputable.

Aim of the study: Description for the first time in Poland of the rare phytophagus Siobla sturmii on an invasive, alien species – Impatiens parviflora, and an attempt to determine its impact on the process of domestication of this species.

Material and methods: Studies were conducted in the Drawa National Park and the Wigry National Park, where the Impatiens parviflora entomofauna was studied. Compact stands of the plant were selected using the floristic inventory method and the occurrence of phytophages on randomly selected individuals was assessed. At each site the phytophage species and the percentage green mass loss were determined.

Results and conclusions: These observations indicate the adaptation of S. sturmii to a new host – Impatiens parviflora in Europe. This is the first record of S. sturmii in the western part of Poland – in the Drawa National Park, where it was found on the leaves of I. parviflora, leading to the leaf mass loss covering 80% of the leaf blade. It also occurred in sites free of its main host plant – Impatiens noli-tagere, which suggests its full adaptation to a new host.