February 16, 2013

A braconid wasp and global warming

In previous posts I have "profiled" several species of braconid wasps which were interesting or significant for some reason (large species, important parasitoids of major pests, potential interest in conservation biology, taxonomic complexes, etc). Today I will introduce a species that might be shrinking its distribution due to warmer temperatures.

The microgastrine wasp Microgaster deductor Nixon (1968) is a very distinctive braconid, and can be easily separated from all Holarctic species of Microgaster based on its tarsal claws, which have a lobe. 
Microgaster deductor, color photo of a female specimen from Churchill, Manitoba, Canada, deposited in the Canadian National Collection of insects. The drawings are taken from the original description (Nixon, 1968) to show details of  the tarsal lobe (red arrow) and head in frontal view.
Until very recently the species was thought to be restricted to northern areas of Europe, in the Western Palearctic. But in 2008 I found in the Canadian National Collection many specimens collected in 1940-1950 from Chuchill, Manitoba, Canada. That locality was the first record of the species for North America. In 2010 the species was collected again in another Canadian locality: Tuktoyaktuk, Northwest Territories. Thus, and based on the information currently known, M. deductor seems to be distributed in sub-Arctic or Arctic areas of Europe and North America.

Distribution of Microgaster deductor (blue dots) based on literature records (Europe) and CNC specimens (Canada). There is a record from Poland that is not included here pending verification of its accuracy.

Based on the number of specimens and the dates they were collected, the species was, by far, the most abundant microgastrine wasp in Churchill 60 years ago (between 1940-150). M. deductor was not only abundant, but also collected from late June to early August -i.e. throughout most of the "insect season" in that northern locality, which usually runs from late May to early September.

But, in spite of intensive and comprehensive collecting going on in Churchill and surroundings for the last 7 years (2006-2012), the species has never been found again. This is a significant change, from being the most abundant species in the locality to be totally absent. In a recent paper reporting the diversity of Microgastrinae in the area, the dramatic change in species composition was attributed to warmer temperatures, which have been rising in the region for the past 50 years or so. While other species were found to be in the same situation that M. deductor, none was as dramatic as this case.

Churchill, which is almost 59° N of latitude, is an area of transition between the boreal forest and the tundra, limited to the north by the immense Hudson Bay. If it is true that the species has been extirpated from Churchill because of global warming, it did not have a place to move north. It would be a classical example of extinction by attrition -the species cannot move farther north and would be essentially "doomed" -at least in that particular region.

Fortunately M. deductor seems to exist in other localities further north, as it was proved by the specimen collected in Tuktoyaktuk (which is at 69° N or 10 degrees northern than Churchill). At present we know nothing about the potential distribution in other areas of the north of Canada (and perhaps Alaska). And, of course, we do not know if the wasp would be as abundant there as it once was in Churchill. 

Whatever is happening, we need more studies on the species to find out more about their potential populations in the Arctic. As with polar bears, we might be witnessing a significant reduction on the distribution of this braconid wasp (which potentially could affect its survival, in the worst case scenario). Yes, braconid wasps are not as big or charismatic as polar bears, and trying to protect and study more this species may well be an uphill battle. But it is nevertheless a battle worth fighting, and I am willing to fight a battle for that small wasp.

Stay tuned for more stories about significant species of braconid wasps...

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