November 19, 2012

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.

Being so big (well, size is always relative, depending on the taxonomic group one is talking about) this is one of the few microgastrines that can actually be seen in the wild! In fact it is the only Apanteles species whose adult specimens have been recorded as feeding on plants, namely two wildflowers from the families Apiaceae and Asteraceae. This wasp species was described from Quebec, in 1886, by the Canadian priest and naturalist, Léon Abel Provancher -known as "The Father of Natural History in Canada". 
Apanteles crassicornis (Provancher, 1866). See the elongated face and large glossa. 
Photo of the holotype of the species, deposited in Laval University, Quebec.

And yet, we know nothing about the caterpillars that this large species parasitizes!

One might be tempted to think that, being such a large wasp, its host caterpillar should be a large one as well... but this assumption may be wrong. There are many records of small microgastrine wasps attacking large caterpillars, one of those examples can be seen in this Youtube video. The reason behind that is that microgastrines can be gregarious (i.e. more than one wasp develops from one host caterpillar). In fact, most of the Apanteles species for which we know their host records are gregarious, meaning that the size of the caterpillar does not necessarily correlates with the size of the adult wasp. One thing seems certain, though: with the size that the adult Apanteles crassicornis reaches, the species should likely be solitary (i.e. one wasp develops from one host caterpillar).

Other than that, we know nothing else. It would be awesome if someone interested in rearing caterpillars could come with the host of this Apanteles species. We just need to start rearing caterpillars from the areas where A. crassicornis has been recorded. Below I provide two maps with the known distribution of the species. The first one shows, in green, all provinces and states for which there are records in the scientific literature [it was generated by that incredibly useful database that is Taxapad].

The second map, which is better seen by clicking on it to open a larger file, contains locality records (blue circles), gathered from specimens deposited in the Canadian National Collection of Insects. The red square shows the westernmost and southernmost record of the species (in Arizona, unspecified locality) which comes from the literature and may prove to be wrong. That map was generated using SimpleMappr. [I want to thank David Shorthouse for making freely available such a nice program to the researcher community].

I expect to refine that information soon, with a detailed description of the species and more photos, which will be uploaded in my homepage at  the Canadian National Collections of Insects, Arachnids and Nematods (CNC, Ottawa) website. I will post here when that is ready.

Time to start searching! (Well, not exactly now but next spring, when caterpillars will appear again in the regions where the species inhabit).

[I want to thank Dr. Jan Klimaszewski (René Martineau Insectarium, Laurentian Forestry Centre), Gisèle Wagner and Jean-Marie Perron (Collections de l'Université Laval), from Sainte-Foy, Québec, for their invaluable assistance during my visit to their institutions, and for kindly loaning me the holotype specimens of Microgastrinae wasps described by Provancher]

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