The jewel beetle Chalcophora mariana (jättepraktbagge) in the High Coast area

Chalcophora mariana is a beetle that is rare in Sweden and presently only occurs in a few areas in Västernorrland and Gävleborg county. We analysed recent data available for the species to better understand potential limitations for the persistence of the species. Winter temperatures at Swedish sites of the species are unlikely to be at the extreme edge of what the species can tolerate as several sites outside of Sweden experience even colder minimum temperatures. However, the average temperature at Swedish sites between April and August is lower than at other sites the species is known to occur. This supports the prior suggestion that a sunexposed microclimate is very important for the Swedish population. A yearly hatching hole survey of the species in Skuleskogen national park showed a moderate decrease of hatching holes between 2011 and 2018 (rate of decrease: –(0.12-0.15). A single unusually high count early on in the monitoring period on a single deadwood item was responsible for much of the decrease. This deadwood item likely represents a highly suitable substrate in decline. In exploratory models we found that the number of hatching holes per year was positively associated with a higher number of days with good flying conditions in the year of hatching and an earlier occurrence of the first day with good flying conditions in the year of hatching and six years prior to hatching (roughly the assumed larval period). We also found that deadwood items receiving higher radiation values produced a larger number of hatching holes. However, these results are based on data with a narrow temporal and spatial extent and do not support the inference of robust conclusions. Therefore, the results should be regarded as tentative and will need to be confirmed, rejected or refined when more data become available. We give recommendations for the collection of additional data.