Insect biodiversity and forest pests-the case of ground beetles (Col.: Carabidae) and cockchafers (Col.: Melolonthinae) in south-eastern Poland

Insects can play different roles in forest ecosystems. Ground beetles (Col.: Carabidae) are con- sidered to be a group of insects that are very sensitive to changes in environmental conditions; therefore they are often used as bioindicators of changes in forest ecosystems. Cockchafers (Col: Melolonthinae) are known to be significant forest pests by feeding on the roots of plants (grubs) and tree foliage (adults) resulting in serious damage to tree plantations and forest stands. The aim of study was to assess the effect of disturbances resulting from the long-lasting occurrence of cockchafers on the diversity of ground beetles collected in the affected and non-affected stands. The research was done in two Forest Districts (Lubaczow and Narol) on 141 plots established on a regular grid. Pitfall traps were installed in the centres of the plots and checked during the vegetative period of 2018. The plots with traps were classified (classes 0-4) according to the number of years with a recorded occurrence of cockchafers in the 4-years period covered by the analysis. The number of species, as well as Shannon-Wiener and Margalef indices were used to characterize the diversity of ground beetles. The mean number of species collected increased along with the classes reflecting the number of years with a recorded occurrence of cockchafers. This pattern was not fully reflected by the diversity indices, but their values were higher in the classes with a longer lasting occurrence of cockchafers. We posit that the observed increase in species richness corresponding to the occurrence of cockchafers is related to changes in the food accessibility favourable for several trophic guilds of carabids (predators - hemizoophages - phy- tophages). The increase in the abundance of dying/dead plants damaged by the feeding grubs may be related to the properties of forest litter that may be more favourable for some carabid species. The demonstrated variability can result from disturbances caused by cockchafers and from changes in species composition of ground beetles in analysed stands based on various char- acteristics, such as age or composition of tree species.