Gergely Várkonyi:
HOST-PARASITOID FOODWEBS OF SAPROXYLIC INSECTS AND THEIR SUCCESSION IN NATURAL FORESTS

This research project is part of Deficiently known and endangered forest species in Finland, called PUTTE, running 2003 - 2007.

We study the effects of tree species, microhabitat (part of the tree) and decay stage on the structure of saproxylic insect communities. Our study sites are situated in five protected old-growth forest areas in province Kainuu, eastern Finland, as well as in a large untouched forest continent in the adjacent Russian Karelian municipality Kostamus. Our study tree species include the most typical boreal forest trees, i.e. Scots pine, Norway spruce, silver birch and trembling aspen. We felled down 20 large trees of each species in each study area, making a total of 480 trees. To keep the structure of these fully or closely natural-state forests undisturbed, we chose the study trees to be situated at a minimum of 100-m distance from each other. Each study tree has been sampled once a year since 2004 onwards, i.e. a base-, mid- or canopy-trunk or a twig sample has been taken and transported to the laboratory of Friendship Park Research Centre in Kuhmo. Each sample has been divided into two equal parts, one of which has been searched immediately for – mostly immature – insects, while the other part has been put into a rearing sack in order to collect emerging adults. The insect communities dwelling in these samples consist of insects feeding on decaying wood or fungi as well as their natural enemies, including predators and parasitoids. The direct search for – e.g. parasitized – larvae in the other half of the each sample helps us to confirm the possible host-parasitoid relationships to be found in the reared material. To identify the typically undescribed immature stages of both hosts and parasitoids we use sequencing of variable genes and a large DNA sequence database. Field data also include results of the detailed inventory of living and decaying trees around each study log as well as of fungi dwelling on the sample logs (first inventory in 2004, second to be in 2006).

During 2004-2005 we preserved insect samples in altogether ca 8500 vials, which material is now being subject of identification by a wide international group of entomologists. The main insect groups included in this study are beetles, several nematoceran dipteran families, brachyceran and cyclorrhaphan flies, parasitic wasps as well as psocopterans. Beetle samples contain so far some 6000 individuals and ca 140 species.

Our study material will be used to describe the saproxylic insect communities dwelling in different trees, in different parts of the study tree species as well as the successional changes following the decaying process of coarse woody debris. We shall also explore which factors describing forest structure if any affect the incidence of saproxylic species. Further questions to be explored include more specific problems in the biology of parasitoids, e.g. how wide host ranges different parasitoid wasps have got and what is the mechanism of host detection by the female parasitoid.

Additional information:

Gergely Várkonyi, Kainuun Ympäristökeskus, Ystävyyden puiston tutkimuskeskus, Lentiirantie 342 B, 88900 Kuhmo, Tel. +358 50 3520 883.