Metacommunity Ecology Group

Spatial population biology of parasitoids

Through long-term monitoring of the butterfly Melitaea cinixa and its parasitoids in the Åland islands, as well as detailed study of the behavior and natural history of individual species, we have started to understand spatial aspects of host-parasitoid population dynamics, beyond what can be addressed in other natural host-parasitoid systems. We have shown that parasitoid metapopulation dynamics are influenced not only by host dynamics and habitat connectivity, but also by host plant distribution, hyperparasitism, temperature mediated phenology, and more recently a plant pathogenic fungus.

van Nouhuys, S. and Punju, E. 2009 Coexistence of competing parasitoids: which is the fugitive and where does it hide? Oikos, in press

van Nouhuys, S. & R. Kaartinen 2008. A parasitoid wasp uses landmarks while monitoring potential resources. Proceedings of the Royal Society B, 275: 377-385 PDF

van Nouhuys, S. and Laine, A-L. 2008 Population dynamics and sex ratio of a parasitoid altered by fungal infected diet of host butterfly. Proceedings of the Royal Society B, 275: 787-795 PDF

Elzinga, J. A., van Nouhuys, S., van Leeuwen, D. J., Biere, A. 2007. Distribution and colonization ability of three parasitoids and their herbivorous host in a fragmented landscape. Basic and Applied Ecology, 8: 75-88 PDF

Kankare, M., van Nouhuys, S., Gaggiotti, O., Hanski, I. 2005. Metapopulation genetic structure of two coexisting parasitoids of the Glanville fritillary butterfly. Oecologia, 143: 77-84 PDF

van Nouhuys, S. 2005. Effects of habitat fragmentation at different trophic levels in insect communities. Annales Zoologici Fennici, 42: 433-447 PDF

van Nouhuys, S., & G. C. Lei. 2004. Parasitoid and host metapopulation dynamics: the influence of temperature mediated phenological asynchrony. Journal of Animal Ecology, 73: 526-535 PDF

van Nouhuys, S., & I. Hanski. 2002. Colonization rates and distances of a host butterfly and two specific parasitoids in a fragmented landscape. Journal of Animal Ecology, 71: 639-650 PDF

van Nouhuys, S. & W.T. Tay. 2001. Causes and consequences of small population size for a specialist parasitoid wasp. Oecologia, 128: 126-133 PDF

van Nouhuys, S. & I. Hanski. 1999. Host diet affects extinctions and colonizations in a parasitoid metapopulation. Journal of Animal Ecology, 68: 1248-1258 PDF

Following are brief descriptions of some current projects:

Sex ratio variation in parasitoid populations

Parasitoid populations can differ in sex ratio (proportion of individuals male) because female Hymenoptera (ants bees and wasps can control the sex of each egg that is laid. Local mate competition predicts that if individuals mate locally then a mother should produce as few males as possible to assure that her daughters are mated. We predict that for some parasitoids, population size and connectivity affect parasitoid sex ratio such that the fraction male will decrease with decreasing host population size and connectivity. This is because in small and isolated populations most progeny will only have close relatives around to mate with. We expect the effect of habitat isolation to be weak for H. horticola because it is mobile and mating is delayed, and stronger for C. melitaearum which is less mobile and has been observed to sib mate, and M. stigmaticus because it is at a high trophic level so experiences a more fragmented landscape. We are using field survey and a large-scale field experiment to test these predictions.

Related papers:

van Nouhuys, S. and Laine, A-L. 2008 Population dynamics and sex ratio of a parasitoid altered by fungal infected diet of host butterfly. Proceedings of the Royal Society B 275: 377-385 PDF

Fox L. R., D. K. Letourneau, J. Eisenbach & S. van Nouhuys. 1990 Parasitism rate and sex ratios of a parasitoid wasp: Effects of herbivore and plant quality Oecologia, 83: 414-419 PDF

What maintains a uniformly low rate of parasitism?

The parasitoid wasp H. horticola parasitizes young larvae still inside the eggs of M. cinixia.   The butterflies lay eggs in clusters. Hyposoter horticola parasitize about 1/3 of the larvae in each cluster, and practically all clusters get parasitized, each by a single wasp.  There are several possible explanations for this apparent constrained rate of parasitism, some of which we are studying experimentally and using mathematical modeling.  Fore instance:

Butterfly-parasitoid hyperparasitoid interactionOne generally thinks of rate of parasitism as an outcome of the interaction between a host and parasitoid. But the parasitoid is actually sandwiched between the host and its own secondary parasitoids. Thus, how a parasitoid distributes progeny among hosts may be explained in part by the parasitoids relationship with the secondary parasitoid. Preliminary data suggest that secondary parasitism by M. stigmaticus is positively density dependent at the scale of butterfly larval group. Perhaps the rate of primary parasitism must be low enough to prevent high secondary parasitism, but high enough to allow persistence given the host metapopulation dynamics. To test this idea we are experimentally measuring the degree and spatial scale of density dependence of hyperparasitism, the behavior of H. horticola from areas it is absent, and constructing a quantitative model of the interaction.

Time allocation The hosts in a single cluster become suitable for parasitism over several hours.  It is possible that a wasp parasitized all that are ready upon arrival, and would have to wait to parasitize the rest.  Perhaps their success rate is higher if they leave to forage for another egg cluster, rather than wait.  This would depend on the mortality of egg clusters, and the chance of the wasp successfully parasitizing more egg clusters.