March 14, 2013

The beautiful complexity of caterpillar-parasitoid food webs

This morning the good friend and colleague Dr. Jan Hrcek sent me a copy of his last paper on caterpillar-parasitoid food webs in Papua New Guinea (PNG). In the past we had collaborated regarding some work on braconid wasps, especially microgastrines. Jan has been researching caterpillars and their parasitoids in PNG for several years and has published quite a few interesting and amazing papers on the topic.

The title of the paper that he sent me today is "Parasitism rate, parasitoid community composition and host specificity on exposed and semi-concealed caterpillars from a tropical rainforest", and was published in Oecologia. It documents parasitism rate and host specificity in a highly diverse caterpillar-parasitoid food web encompassing 266 species of lepidopteran hosts and 172 species of hymenopteran or dipteran parasitoids from a lowland tropical forest in PNG.

I strongly recommend the reading of this paper -which, unfortunately, is not open access, but I guess the interested reader could contact Jan to ask for a copy. Anyone rearing caterpillars and/or dealing with caterpillar parasitoids will find the data reported there useful. I found the comparison between parasitoids of external and semi-concealed host very telling, even though some results are not in line with some preconceived ideas -such as ichneumonid wasps being more generalists than tachinid flies. But preconceived ideas are just that, and field data may change our "old thinking" on parasitoids. This study is based in collecting almost 40,000 caterpillars in the wild, with a rearing success of more than 11,000 adult Lepidopterans and over 1,500 parasitoids (wasps and flies) which represented 12% of parasitism rate. That is certainly a sizable database to extract some valid conclusions -although it may be risky to make generalizations to the world fauna based on only one study site, but I look at this as a very valuable piece of information.

And, of course, I liked the fact that braconids, and especially Microgastrinae, are considered the most suitable group for the biological control of caterpillars (but I am totally biased here ;-)

Most importantly, it is an eye-opener to realize that there has been no resarch like this in the past. Even the most comprehensive studies rearing caterpillars in several regions of the world -Jan cites in his paper a good number of such studies- have not fully addressed the potential differences between parasitoid communities of exposed and concealed (or semi-concealed) hosts. We still know so few about this and many other related topics!

After I read Jan's paper I went to briefly check some of those past researches that he mentioned. And I spent some time analyzing the diverse approaches, merits and/or shortcomings of those studies. There are many logistics difficulties, lack of resources and time constraints that limit what we can do -especially in tropical, hyperdiverse areas... I will try to cover those topics in future posts.

It is never a simple thing this endeavour of rearing caterpillars and study their parasitoids!


  1. Hi Jose,

    Thanks for sharing. I wish to read it so have asked pdf from Dr. Jan Hrcek.


  2. Hi Ankita,

    I apologize for my delay in replying to your comment -too many things going on now. Anyway, better late than never... ;-)

    I am glad that you were interested in that paper. I hope to continue to use this blog to bring the attention on interesting papers/data like that.

    Thanks again for your interest!