The researchers from the Biodiversity Unit of the University of Turku have studied the diversity of tropical parasitoid insects for almost 20 years already. During their research, they have discovered large numbers of new species from different parts of the world. In the newest study, the research group sampled parasitoid wasps of the genusAcrotaphus, which parasitise spiders. The diversity of the insects was studied in e.g. the tropical Andes and the lowland rainforest areas of the Amazon. The research was conducted in cooperation with the Brazilian INPA (Instituto Nacional de Pesquisas da Amazônia) research unit.

-Acrotaphuswasps are fascinating because they are very sizeable parasitoids. The largest species can grow multiple centimetres in length and are also very colourful. Previously, only 11 species of the genus were known, so this new research gives significant new information on the diversity of insects in rain forests, tells postdoctoral researcher and lead author of the new study Diego Pádua, who has worked both for the INPA and the Biodiversity Unit of the University of Turku.

The parasitoidAcrotaphuswasps parasitise on spiders. A femaleAcrotaphusattacks a spider in its web and temporarily paralyses it with a venomous sting. After this, the wasp lays a single egg on the spider, and a larva hatches from the egg. The larva gradually consumes the spider and eventually pupates.

- TheAcrotaphuswasps we studied are very interesting as they are able to manipulate the behaviour of the host spider in a complex way. During the time period preceding the host spider's death, it does not spin a normal web for catching prey. Instead, the parasitoid wasp manipulates it into spinning a special web which protects the developing pupa from predators. Host manipulation is a rare phenomenon in the nature, which makes these parasitoid wasps very exciting in terms of their evolution, tells Ilari E. Sääksjärvi, Professor of Biodiversity research from the University of Turku.

The University of Turku and INPA continue to study the diversity of the parasitoid wasps in collaboration in the west Amazon area and in the Andes. On each research trip, the researchers discover many new species with unknown habits.