Abstract: Michal Holec & Jindřich Havelka Dr. Michal Holec (contact author), Bc. Jindřich Havelka, Jan Evangelista Purkyně University, Faculty of the Environment, Králova výšina 7, 400 96 Ústí nad Labem, Czech Republic. E-mail: holec@fzp.ujep.cz; jihanek@centrum.cz Myrmecol. News 10: 107 The leaf damage caused by chewing insects and an abundance of leaf sap-sucking aphids in an oak forest habitat were studied in five localities affected by red wood ants (Formica rufa Linnaeus, 1761 group) in the České Středohoří Mountains (Litoměřice, North Bohemia). Preliminary results from July 2006 are presented. The effects of the ants were studied by (1) comparing one locality with red wood ants (Strážiště Hill) and four control localities without or with only a low red wood ant abundance, and (2) using an experimental design where half of the studied oak trees in each locality were isolated from ant access through the use of petroleum jelly barriers. The aphid density was…