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!

A braconid wasp in the COSEWIC List?

The Committee on the Status of Endangered Wildlife in Canada (COSEWIC) exists to provide Canadians and their governments with advice regarding the status of wildlife species that are nationally at risk of extinction or extirpation. Its committee of experts assesses and designates which wildlife species are in some danger of disappearing from the national territory. As part of  its work, COSEWIC produces a Candidate List of species. I strongly recommend to anyone interested in the protection of the Canadian nature to visit the COSEWIC website, and to support their work and that of similar organizations. [Disclaimer: I do not work for COSEWIC, nor I am involved with their efforts in any capacity].

My interest in COSEWIC, and the reason I am writing this post today is to discuss the POSSIBILITY of including a parasitoid Braconidae wasp within their list. Is that a real thing? Or am I just getting too excited with my subject of research?

Let's look at the facts and try to be impartial. COSEWIC List includes quite a few arthropods species. Which in itself is something truly amazing, especially in this world that usually focus its conservation efforts in large, charismatic fauna -conservation efforts also prioritize the flora, but I will leave plants out of this comment and will restrict myself to animals for the time being. 

Small animals, like insects, tend to be almost completely overlooked... unless they are "charismatic" by themselves, e.g. a beautiful butterfly, a conspicuous bumble bee, a colorful ground beetle, a large dragon fly, etc. But a small parasitoid wasp (2.5 mm long)... are you kidding me? Who cares about THAT?

Well, as they say "no harm in trying", and I am trying today to present the case for a first parasitoid wasp to be considered by COSEWIC: the microgastrine species Apanteles samarshalli Fernández-Triana, 2010.

The species was described very recently, in 2010, from specimens found mostly in southern Florida, United States (Everglades and the Florida Keys). I have also found additional specimens in two countries of Central America (data from unpublished studies). 

But, the original description also recorded the species from one Canadian locality: Rondeau Provincial Park, in southwestern Ontario. Rondeau truly honours its reputation of having species commonly found at much southern latitudes, because the single specimen collected there (in August of 1973, and deposited in the Canadian National Collection of Insects, Ottawa) happens to be, by far, the northernmost known for the species.

Forest Pest Management Forum

This week Ottawa hosted, once again, the Forest Pest Management Forum. This is an annual meeting where people from all over Canada (and a few from the United States) gather together to share updated information about forestry pests and its management in the country. 

I have never been to those meetings, but this year a good friend and colleague, Dr. John Huber, from the Canadian Forestry Service and the Canadian National Collection of Insects (CNC) in Ottawa, suggested me to attend. And I was seriously planning to go when some unexpected complications at work prevented me to do it. 

As a "consolation prize" I ended checking the website of the meeting to at least have a sense of what was going on there. First I found a nice compilation of pdf files with the proceedings of past meetings. Anyone interested in the topics of Entomology, Forestry and Pest Management should take the time and revise that valuable source of data. There are tons of information there. One of the most interesting, in my humble opinion, is to see the historical pattern of pests, within the country and in individual provinces. You can follow the evolution of different pest problems that Canadian forests have experienced during the past years by just reading those proceedings.

I went back only seven years, up to the proceedings of the 2005 meeting. But found quite a few interesting details, and this post is to share what I found about Lepidoptera pests.

First of all, I could compile a list of 119 species and 20 families of Lepidoptera caterpillars that have been considered forestry pests in Canada (see detailed list at the end of this post).  Half of all species belong to just two families: Geometridae (27%) and Tortricidaae (26%), and seven families account for three quarters of the species.

Lepidoptera considered as pest of Canadian forests (grand total: 119 species and 20 families). For an explanation of the data sources, see detailed list of species added at the end of this post.

Of course, most of those species are of low significance and cause minor affectations to forestry (or the damage is just too sporadic or too sparse to consider them of real importance). Actually less than a dozen species can be considered as serious pests. Still, this grand total of 119 species should remind us of how quickly things can go wrong with an insect pest. Unfortunately, the next "new pest" outbreak might be just around the corner...

What do we know about the largest Apanteles species in North America?

In a previous post it was mentioned that the braconid wasps of the subfamily Microgastrinae comprise specimens ranging from 1.5 to 8.0 mm of body length. The truth is that most of the microgastrines are rather small, usually 2.0 to 3.5 mm long. The "record" of 8 mm is reserved for "giant" specimens of Larissimus, a tropical genus in South America. However, in North America there are very few species that surpass the 4 mm mark, and most of those species are in the genera Microgaster and Protomicroplitis...

Among the largest specimens of microgastrine wasps in North America, the species Apanteles crassicornis stands on its own with around 5 mm of length. That species is also noteworthy because of its elongate face and enlarged glossa, which is supposedly related to the gathering of pollen or nectar. 

Apanteles crassicornis (Provancher, 1866). Antennae and legs are missing some segments. Photo of the holotype of the species, deposited in Laval University, Quebec.

An overview of braconid wasps in Canada

Braconid wasps are the second largest group within Hymenoptera (the insect order that comprises bees, stinging wasps, ants, sawflies and parasitoid wasps). The last version of Taxapad records 956 described species of Braconidae for Canada. Of course, that is just the total of species that have been given scientific names by taxonomists. But it does not account for the many undescribed and/or unrecorded species that remain to be discovered. How many species are actually out there in the Great White North?  

Main subfamilies of Braconidae (Hymenoptera) in Canada. Total number of species: 956 [based on Taxapad (2012)].

While it is impossible to be certain, it is likely that at least twice the current figure, or about 2,000 species of braconid wasps will be found in Canada when all is said and done. 

Think about that for a second. The only group of living things (excluding perhaps microorganisms) that is more diverse than braconids wasps is yet another group of parasitoid wasps: Ichneumonidae, which happens to be the sister group to braconids. Ichneumonid wasps currently comprise almost 3,000 species in Canada (2,834, according to Taxapad). Nothing else comes even close to those figures -and the same situation is probably found in most other areas of the planet. We are talking here about the biodiversity heavy-weights.

Two thousand species of braconid wasps in Canada is a great number, and it amazes to think that we are still missing ONE THOUSAND species to be recorded -let alone studied in detail! The vast majority of those tiny wasps play a capital role in the natural regulation of herbivores -which might otherwise become pests of our crops and forests. Thus, this is not only a matter of scientific inquiry, but also a practical issue with economical implications.