A series of sedimentary profiles derived from the Lac Long Inférieur peat-bog (2090 m altitude, southern Alps) enabled the tracing of the evolution of successive fossil insect assemblages (Coleoptera, Hymenoptera Formicidae, Diptera Bibionidae, Trichoptera, Megaloptera and Nevroptera) from the Würm deglaciation to the present in this part of Vallée des Merveilles. This evolution reflects the climatic changes and hence the vegetation changes, as well as the human impact on the environment since neolithic times. During deglaciation, an episode marked by very poor fossil insect assemblages was followed by one with abundant boreo-alpine Coleoptera dependent on melting snow and steppe Coleoptera. This episode corresponds to the Younger Dryas climatic deterioration (10 970 ± 210yr BP; 10 430 ± 210yr BP) during which a steppe vegetation prevailed. The sudden fall in the number of insects belonging to cold environments marks the beginning of the Holocene warming. During the Preboreal and the Boreal period (8801 ± 54 yr BP; 8692 ± 53 yr BP) these insects disappear almost totally. On the other hand, Coleoptera mostly living at the tree-line and at forest margins increase and reach a maximum at the end of the Boreal. Thereafter (Atlantic, 8087 ± 58yr BP; 5678 ± 50yr BP) they decrease to the benefit of forest insects. This development corresponds to an elevation of the tree-line during the Atlantic and the Sub-boreal (4770 ± 300yr BP; 3740 ± 160yr BP) and to a thicker forest cover. Coleoptera dependent on Abies and Larix appear at this time. The final entomological event occurs at the end of the Sub-boreal and in the Subatlantic (2660 ± 190yr BP): it is characterised by a regular decrease of tree-dependent taxa. This development is attributed to human action. Copyright © 2001 John Wiley & Sons, Ltd.