Importance of rearing caterpillars and its parasitoids

A month ago I had the great opportunity and honor of visiting Mark Shaw in Scotland, and Kees van Achterberg in the Netherlands. Today I will be writing about my stay with Mark, and what I learned from his extraordinary collection.

The first thing I realized was how few I know on parasitoid biology, especially compared to what Mark knows. It is a humbling experience to listen to him talking about particular species of wasps attacking particular species of caterpillars -and on determined plants, at different moments of the season/year! Here in North America we are light-years away of that kind of knowledge. By comparison, we know nothing.

Another thing I learned was to not be fooled by the appearances. Mark's collection (photos below) might seem a bit rustic... but make no mistake, you are contemplating one of the greatest resources available about biology and ecology of Lepidoptera-parasitoid wasps.

 

The collection -which in due time will be transferred to proper wooden drawers and deposited in the National Museums of Scotland, in Edinburgh- mostly comprises thousands of specimens collected by Mark during the last 2-3 decades. Decades he spent patiently rearing caterpillars, mostly in the United Kingdom, but also in many places across Europe. There are hundreds of new host records, and valuable ecological information on the wasps species, mostly Braconidae, but also Ichneumonidae and a few other families of Hymenoptera parasitoids.

During my 5-days visit I only had time to study 2 genera of Microgastrinae, and could not even finish with them. Going through the collection I was amazed to see the richness of the data gathered by Mark. And, as a greedy person gathering golden coins from a treasure coffin, I spent my last two days frantically recording data and typing notes in my laptop... 

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!

Updated list of Nearctic Microgastrinae (Hymenoptera: Braconidae)

This post introduces a new way I plan to use in this blog to share taxonomic information. I will start providing dynamic species lists -in the sense that data are new/current as of the date they are posted, and they will be kept updated as I post more information during the next few months.

The reader should check the page in this blog named "Species Lists". It provides updated information about species from a particular region. The first list posted includes all Microgastrinae known from the Nearctic Region (Canada, Greenland, and United States). You can access that data by clicking on the top left corner of the blog, or just by clicking  here.

A total of 338 Microgastrinae species (321 of them already described) are accounted for there, making it the most comprehensive list assembled so far for the region. Let's briefly summarize what was known before.

The last Nearctic list was published by Whitfield (1995). It included 288 microgastrines -282 when removing some questionable records: at least 5 species introduced into North America as biological control agents which are not likely to be established; and also cited Glyptapanteles longicornis as a valid species, overlooking its synonymization under G. pallipes by Papp (1983). 

During the 18 years since the publication of Whitfield's paper, 27 new species with Nearctic distribution have been described, and a handful of species already described from other regions have been recorded for North America.

For example, Fernandez-Triana (2010) provided an updated list of 225 species for Canada and Alaska, including 29 species determined only to genus level. Some of those undescribed species are also mentioned in the present list, because they are expected to be published soon (and when they are, the blog will update that information accordingly). However, I have left may more out -species that are clearly new records for the Nearctic but are not accounted for now, pending further study.

The taxonomic conundrum of Cotesia xylina and Cotesia yakutatensis

One of the main purposes of this blog is to provide comments on species of Microgastrinae that are of interest to a broader audience. I am still thinking on how to organize those posts to make them more useful to potential users, and hopefully soon will come with a system to do that. In the meantime, I am tagging them with the label "Species Profile", to make it easier to search and retrieve that kind of data.

Today I will briefly comment on two Nearctic species of Cotesia that present an interesting challenge to taxonomists and biocontrol workers alike: Cotesia xylina (Say, 1836) and C. yakutatensis (Ashmead, 1902).  Both species are only found in the Nearctic region, although yakutatensis has a wider and more northern range, extending up to Alaska in the West and up to Greenland in the East.

Distribution of Cotesia xylina and Cotesia yakutatensis. Data taken from Taxapad (2012). The coloured areas represent the Provinces/States where the species have been recorded, but no information on exact localities is shown here.

Both species have been reared from several species of Lepidoptera, mostly from the family Noctuidae, with some of the hosts representing agricultural pests. The validity of some records is questionable, especially the ones from Pyralidae and Sphingidae -those were reported in papers before 1920 (mostly late XIX century), and the wasps species may just have been missidentified.


C. xylina has been recorded parasitizing eight species of caterpillars: Epiglaea apiata, Mamestra configurata, Peridroma saucia, Xestia c-nigrum, Xylena nupera (all noctuids), Evergestis rimosalis (Pyralidae), Lampara bombycoides, and Smerinthus jamaicensis (Sphingidae). As written above, the last two records are suspicious.

As far as I know, there is no published paper providing illustrations or drawings of C. xylina, so here I present one colour photo taken a couple of years ago in the CNC.  

Open for business: Apanteles fumiferanae

The microgastrine wasp Apanteles fumiferanae Viereck is one the most important Braconidae -as forest pest management concerns- in North America. Based on specimens available in collections, it is the most common braconid parasitoid reared from the spruce budworm Choristoneura fumiferanae (Harris) (Lepidoptera: Tortricidae), which in turn is one of the major forest pests in the region.

Very few pests rival the spruce budworm in importance, and thus this lepidopteran species has been extensively studied over the years. There are hundreds of papers covering details of its biology, ecology, damage and control (biological, chemical, integrated). As part of those studies, for many years its caterpillars have been collected and reared for parasitoids, providing perhaps the best information ever available for a single forest pest in the Neartic. And still there are many details to be researched and understood!

Some recent papers summarize what we know until now. For example, an excellent analysis of the complex relationships between the spruce budworm and its parasitoids/hyperparasitoids/pathogens, was published by Eldon Eveleigh (Canadian Forest Service, CFS) and ten co-authors in 2007; it can be freely downloaded here. Reading that paper will open anyone eyes regarding the complexities of the food webs in a temperate forest. I especially recommend to check Figure 1 of that paper (which is not for the faint of heart!). One can only image similar analysis for a tropical forest... it is just mind boggling.

From a parasitoid perspective, John Huber, also from the CFS, led a team of four taxonomists to produce a series of papers covering all major groups of parasitoids of the genus Choristoneura in the Nearctic region: chalcid wasps (Huber, 1996), tachinid flies (O'Hara, 2005), ichneumonid wasps (Bennett, 2008) and braconid wasps (Fernández-Triana and Huber, 2010). Those works provided numerous illustrations, keys, and taxonomic notes to help identifying the large fauna of currently known parasitoids (230 species within 106 genera and 13 different families; see figures 155-157 and Discussion in Fernández-Triana and Huber (2010). [Unfortunately those papers can be downloaded for free, except for their Abstracts. However, being one of the authors of the braconid paper, I have plenty of reprints for that one, and would be pleased to send copies to anyone interested].

Which bring us back to the topic of this post: Apanteles fumiferanae. The species is widely distributed in the Nearctic region (there is also a record from Poland, but that might be incorrect). It has been reared from caterpillars of 17 lepidopteran species representing 4 families (although some of those early records, from historical references, are likely to be wrong). Close to one hundred scientific papers have dealt with that wasp species, and there is reason to believe more are needed... Why? Because A. fumiferanae actually comprises a complex of morphologically cryptic species (i.e. species that cannot be easily separate based on external morphology, yet are distinct biological entities).

Numbers matter

This week I was talking to my colleague Caroline Boudreault about the numbers of Braconidae specimens, species, and primary types that we currently have in Ottawa (Canadian National Collection of Insects, CNC). Caroline, an extremely skillful and knowledgeable person when it comes to braconids, had been asked to revise and update the number of primary types here.  

Primary types (i.e. holotypes, syntypes, lectotypes, and neotypes, as defined by Articles 73-75 of the International Code of Zoological Nomenclature) are usually one of the main factors considered when evaluating the weight of a collection. The more the types, the higher a collection is ranked. Because primary types are name-bearing specimens. 

So, how good is the CNC in terms of Braconidae types? According to Taxapad, there are almost 300 institutions worldwide storing primary type material of braconid wasps, altogether representing 20,007 type specimens. And, according to that source, Ottawa is the 5th largest collection in the world, with 683 types (see pie chart below).

Number of primary types (mostly holotypes) stored in 272 collections of Braconidae worldwide (after Taxapad, 2012).

When Caroline added some new data that is not yet in Taxapad, the number rose to more than 720. And then we will be incorporating over 200 new holotypes within the next couple of months (I will write about that development in a future post). Thus, in round numbers, the CNC collection of Braconidae is approaching the one-thousand-types mark. 

Of course, beyond the number of primary types it is also important to know the number of specimens overall, the geographic coverage of the collection per se, and its curation state. We do not know those figures with the same precision as for the types, but below I share what have found out so far.

There are almost 60 cabinets, each with 29 drawers, for a total of over 1,600 drawers with braconid wasps in the CNC (a previous summary mentioned 1,500 drawers of Braconidae, but that number has increased steadily in the past two years). Based on that, and on a conservative average number of specimens/drawer,  my tentative estimate would be around half million of specimens. And that only represents the mounted/pined material; there is a huge collection in alcohol (several thousand vials, as mentioned here), where many more thousands specimens await to be processed and incorporated to the main (dry) collection.

Opportunities of DNA barcoding for taxonomists

A few days ago a paper I co-authored came out in Molecular Ecology Resources. That paper is of relevance to this blog because it releases over 20,000 DNA sequences (gene CO1) from over 2,000 species and 50 genera of Microgastrinae braconid wasps, collected in over 75 countries. The number of sequences made available for free use of the scientific community and the general public it is likely one of the highest ever released. It speaks volumes of the efforts made by the International Barcode of Life or iBOL (among many other institutions, partnerships and initiatives) that are promoting the use of DNA barcoding to help cataloging, studying and describing the amazing diversity of life in this planet. [For those interested in more information about DNA barcoding, there are many resources online to look at, probably an easy way is to just start browsing the iBOL website and related sites mentioned there. Suffice to say that DNA barcoding has many practical applications, but for this post I will only focus on its potential for taxonomists working with parasitoid wasps].

The sequences we are talking about today were amassed during the last eight years and they represent the effort of many scientists and institutions -that explains the long chain of authors being part of the paper. The resources can be accessed using BOLD (The Barcode of Life Data Systems) a magnificent online resource designed to support the generation and application of DNA barcode data.

A view of the BOLD website with summarized information about microgastrinae wasps. Accessed on December 21, 2012. For a larger view and more information on the group click here.

Back to the paper mentioned, it not only releases a significant amount of data, but it also provides suggestions on how to use it in the near future. For example, we considered the sequences to be important in efforts related to: 1) Discovery of cryptic species and description of new taxa; 2) Estimating species numbers in biodiversity inventories; 3) Clarification of generic boundaries within Microgastrinae; 4) Biological control programmes; 5) Molecular studies of host-parasitoid biology and ecology; 6) Evaluation of shifts in species distribution and phenology; and (7) Fostering collaboration at national, regional and world levels. 

All of the above mentioned points are relevant to this blog -and are indeed relevant to biocontrol workers, biodiversity researchers, taxonomists, etc. What is more important: many specimens mentioned in the paper actually come from Canada (~6,000 specimens), or from related areas in the Nearctic or Palearctic regions (+3,000). And that will allow us to advance researches in a way that would not have been possible in the past, before the arrival of DNA barcoding.

Braconid wasps and forest pests in Canada

In a previous post, I analyzed some interesting data coming from the Canadian Forest Pest Management Forum. I could find at least 119 species within 20 families of caterpillars (Lepidoptera) that have been mentioned as pests of some kind to our forests in the past few years. As a taxonomist working with braconid wasps, my next logical step was then to see how many parasitoid species have been recorded out of those 119 lepidopterans.

For such a compilation I used the great resource that is Taxapad. [I have mentioned previously what Taxapad is, and promise that will dedicate a future post to that magnificent database maintained by Dicky Yu (Canada), Cornelis van Achterberg (The Netherlands) and Klaus Horstmann (Germany). Suffice to say for now that Taxapad should be considered as a key tool by many biologists and entomologists, especially those working in biocontrol].

Altogether, 299 species of Braconidae have been found, worldwide, attacking those pest caterpillars. I stress here the world "worldwide" in the sense that those records go beyond Canada to include ANY braconid wasp that has been cited in the scientific literature as a parasitoid of those lepidopterans. It is difficult and very time consuming to separate the sources of information for each individual species and pinpoint the country source. And it is even more difficult to be sure about the certainty of some of those records -some are likely to be wrong for a number of causes. Still, they give us a kind of ballpark estimate about the diversity of parasitoids of forest pest caterpillars. So, for the purpose of this post we can take the worldwide totals as a first approximation to the story of what is going on in Canada.

The first thing that becomes clear is how few we know about the parasitoid of those forest pests. Surely that 299 braconids sounds like an awfully large number of wasps, but the numbers are misleading (see the graph below). Because for 40 (33.6%) of those caterpillar species there is ZERO braconid wasps recorded as parasitoids. That means one third of the caterpillars where we know NOTHING of its parasitoid biology. For another 31 species of lepidopterans (26%) we only know one or two species of braconid parasitoids.

Braconidae species (299) recorded as parasitoids of 119 pests caterpillars of some relevance to Canadian forests. Data source mostly from Taxapad (2012). The numbers on top of each bar represent the actual number of braconids in each category.


On the other side of the spectrum, we have recorded 30 or more braconid parasitoids for 4 species of caterpillars. They represent important pests (such as the spruce budworm or the gipsy moth) which at some point have been the focus of serious rearing efforts from biocontrol workers, resulting in hundreds of research papers. If anything, that should be the example to follow with other pest species that are important as well. 

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...

Why Microgastrinae and why they may interest you

When rearing caterpillars, it is common to find some small parasitoid wasps (1.5-8 mm long), often black or yellow and with rather short "abdomen". They belong to the subfamily Microgastrinae (Order Hymenoptera, Family Braconidae), and are one of the most important groups parasitizing butterflies and moths (Order Lepidoptera). These wasps are key components in the biological control of agriculture and forestry pests; and have also been extensively used in biodiversity, ecological, behavioral and molecular studies. However, its narrow host specificity and extraordinary diversity (more than 2,200 described species, with an estimate of 20-40,000 worldwide) presents an immense challenge. 

Addressing the need of more information about those fascinating insects is the main reason of this website. Tips to recognize different genera, species profiles, new biological data, distribution records, and other comments will be provided in following posts. Also, the readers are encouraged to send any question and/or contribution they may have about microgastrines (or any braconid wasp) parasitizing caterpillars. 

Detailed distribution of species and their host records will be compiled from different sources (mostly mined from the large and rich collection available in the Canadian National Collection of Insects, as well as other collections I have visited and/or borrowed material from). Contents intend to be useful to anyone already working or just interested in rearing caterpillars and their parasitoids. It will hopefully interest workers on biological control, bioinformatics, biodiversity researchers, wasp taxonomists, conservation authorities and entomological societies looking for information of species in particular areas. 

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.