What I found out about the shield bug

A total of 3 105 Thesium alpinum plants were found, distributed among 74 patches situated in 30 landscapes. Canthophorus impressus was present in 25 (34%) of the patches and in 15 (50%) of the landscapes. The occupied landscapes were distributed throughout the studied area with exception of the western-most part. In total, 504 shield bugs were found in the study, distributed on 9.6% of the host plants.

Plant size most important

The summed length of branches on a host plant turned out to be the most influential parameter for the distribution of Canthophorus impressus. Large host plants increased both the probability of presence of shield bugs and the abundance of them. A plant with summed branch length of 350 cm was needed for 50% probability of shield bug presence.

The figure on the right shows the predicted probability of occurrence of a bug on a host plant in relation to summed length of branches. The dotted lines show 95% confidence interval.

South-facing slopes, sun exposure and bare ground

Other important habitat quality parameters on plant scale were aspect of slope, sun exposure and cover of bare ground. The shield bug had higher presence on host plants standing in south-facing slopes or in flat terrain. Furthermore, higher sun exposure and higher cover of bare ground increased both probability of presence and abundance of the shield bug on a host plant.

Abundant host plants in the landscape

Number of plants in the landscape was also among the more important variables for determining the presence of C. impressus. Both the presence on an individual host plant and in a landscape increased with the amount of plants.

The figure on the right shows the predicted occurrence probability of a shield bug in a landscape in relation to the number of plants in the landscape. The dotted lines show 95% confidence interval.

The spatial configuration of the host plants in the landscape, i.e. number of plants in a patch (plant group) or number of patches in a landscape, was not important for explaining the distribution of the bug.