The Glanville fritillary butterfly, Melitaea cinxia (Credit: S. van Nouhuys)
AT A GLANCE Project Information
Project Title: The Parasitoid Ecology Group. Project: Landscape scale foraging of a parasitoid wasp
Project Duration and Timing: The research group was established in 2002 and has been working on this project since 2004, with more intensity since 2012.
researchers’
“That period of time in which the caterpillars are available for parasitism is absolutely tiny – a matter of hours”
by others. Mulling over the many possible explanations for why these individuals might show this level of restraint, they first believed that the mounded formation in which the eggs were laid might physically restrain the wasps from reaching all of them. However, this was shown not to be the case. The group then looked at the possibility that there might be a temporal constraint, in that the restricted time in which the eggs were at the right stage in development might limit the amount of eggs that could be parasitised. This explanation also, however, proved to be wrong. It was only when one of the group’s PhD
students decided to carry out some mathematical modelling on the optimum foraging strategy of the wasps that the
64 investigations finally began
to bear fruit, as van Nouhuys explains: “Using this model, we realised that the longer an individual stays at a particular cluster,
the higher the likelihood that it
will come across eggs that it has already parasitised. Parasitising the cluster thus becomes less efficient the longer the individual stays there. Combined with our knowledge from genetic studies that the wasp would be likely to find another batch of eggs if it were to leave, the decision to leave after a certain percentage of eggs has been used becomes apparent.”
Future work Although her group has gone some way towards explaining the reasons behind the peculiarly uniform parasitism of H. horticola, van Nouhuys believes there is still a lot left to find out. Work continues on the tracking by individuals of multiple resources within the landscape, ascertaining just how similar the wasp’s methods are to those of bees and ants. As well as this, another question remains around the movement between egg clusters. When a wasp has parasitised a cluster, it leaves a scent mark signifying that no one can return there. “A really interesting question is: why, if competition is high, would other individuals obey this rule?” says van Nouhuys. “We don’t know why yet, but they do!”
★ Insight Publishers | Projects
Project Funding: 1) The Academy of Finland Centre of Excellence in Metapopulation Ecology 2) Academy of Finland Research Fellowship Grant
MAIN CONTACT
Saskya van Nouhuys Saskya van Nouhuys is an Academy Research Fellow in the Centre of Excellence in Metapopulation biology in the Department of Biosciences at the University of Helsinki. She leads the Parasitoid Ecology Research group that studies behavioral ecology and population and community ecology of parasitoid wasps in natural populations
Contact: Tel: +358 50 4484452 Email:
Saskya.vannouhuys@
helsinki.fi Web:
www.eeb.cornell.edu/sdv2/ www/
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