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Johanna Ehrnsten 2003: The within-patch movement behaviour of a mobile parasitoid,
Hyposoter horticola. MSc-Thesis.

Many butterfly species have greatly declined worldwide, which means that their specialist parasitoids must be even more endangered. Hyposoter horticola is a very mobile, successful, specialist parasitoid of the endangered butterfly, Melitaea cinxia on the Åland islands. It finds almost all its host populations and constantly parasitises 20-30 % of its host larvae, despite the fact that parasitism is only possible during a short time period before the larvae are ready to hatch from the eggs, that is a couple of hours. It is quite exceptional for a parasitoid to be so consistent temporally and spatially usually populations fluctuate in time and space.

I investigated the within-patch movement behaviour of H. horticola to see if it is possible to study the behaviour of such a mobile parasitoid in the field. I also wanted to find out how much the parasitoid moves within its habitat patches. Furthermore I wanted to find out if H. horticola has got a spatial memory and therefore is so successful in parasitising its host.

The results of my experiment showed that it is possible to study the behaviour of H. horticola in the field. It is a very mobile parasitoid and it also moves considerable distances within habitat patches, probably more than its host does. The results also suggest that H. horticola learns the locations of its host´s egg clusters when they are not yet ready to be parasitised and uses that information later to visit them multiple times and parasitise them when they are ready. Another explanation is that H. horticola uses a long-range odour mark, although long-range odour marks in parasitoids are often water soluble and ephemeral and distances between egg clusters are long.