Invertebrates

Among the invertebrates, the group of arthropods accounts for most of the animal biodiversity and includes insects in particular. For this group of animals, which is the most diverse on Earth and the least well known, it is necessary to use numerous field-collection techniques and to implement them over the long term.

As part of the Life On Trees programme, we use Berlèse devices to extract the fauna from the humus accumulated on the branches. We also collect arthropods manually or by beating the foliage in the crown of the tree. Traps with coloured trays are hung from the branches to collect Diptera and Hymenoptera. Pieces of dead wood from the tree are laid out to collect wood-eating insects. We also placed ant bait in the tree and tested fumigation of the foliage. In order to obtain a more complete picture of the succession of insect species that evolve within the crown according to the different seasons and the phenology of the tree, interception traps (SLAM and Polytrap) are placed in the crown and are collected regularly over the course of a year.

We also carried out an inventory of the species of Heteroceran Lepidoptera present in the immediate vicinity of the study trees. This is in order to gain a better understanding of the diversity of the local moth community, but above all to sample the adult representatives of as many species as possible in order to facilitate, at a later stage, the association of caterpillars collected from the tree itself or from the plant species it hosts with the moths observed.

Some of the collected insects are processed using traditional morphological taxonomy and another part is processed using the DNA metabarcoding method (sequencing of a set of genomes) to obtain a proxy for the number of species contained in these samples based on the number of MOTUs (Molecular Taxonomic Units) differentiated.

We will thus obtain a ‘morphological’ estimate and, in parallel, a ‘molecular’ estimate of the number of insect species collected in the tree.

Despite the combination of all these techniques, we will ultimately only have a partial understanding of the arthropod fauna associated with the tree, since it renews itself over time, but the figures will no doubt already be surprising and revealing of the enormous diversity of insects associated with the tree over a period of one year.