[Odonata-l] Emergence Triggers

[Paul Brunelle]

Hello All:
	This is an interesting string, and quite timely.
	I think the matter is probably much more complex than we currently  
suspect, and the triggers may differ by species, habitat, and  
geography. There are probably more than one trigger per species,  
depending on circumstances. Corbet (1999, pg 243 on) has some  
interesting points, certainly wish we could still discuss them with  
Philip.
	Regarding Nick's L. parvulus. In small primary streams such as the  
species principally inhabits up here, the risk of the water drying up  
completely is greater than with any other type of freshwater habitat  
I am aware of except puddles, and I expect it could happen very  
quickly. When it happens the species might not have to emerge at all  
in the sense of deliberately leaving the water; the water just  
disappears around it and the species may have evolved the ability to  
eclose at that point. Would seem a valuable survival trait.
	Date of emergence of some species is very consistent year to year -  
you can almost set your calendar by H. brevistylus up here, June 24th  
± a day in mainland Nova Scotia. But that is comparatively late  
emergence for the suborder, and the groups which emerge earlier seem  
to show more variance by year. Although Ophiogomphids generally  
emerge towards the end of the first week of June in southern Maine  
and New Brunswick, one year they emerged starting May 22nd.
	Consolidating observation of emergence (reared and natural) would  
make an interesting projects. I'm not aware of anyone taking  
emergence records and consolidating them in a single database,  
although I believe Michael May might be doing so for A. junius.
	I'd be happy to database such records if sent to me - a couple of  
years of records might be very informative, and I've always felt the  
lack of a baseline structure for assessing whether a year is 'early'  
or 'late'. Perhaps we could work out a protocol and make it a DSA  
initiative. Or perhaps someone would like to work towards a paper on  
the subject.
	Regards,
	Paul
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Paul M. Brunelle, BDes, FGDC
4 Hilltop Terrace, Dartmouth, NS, Canada, B2Y 3T1
(about 45°N) 902-423-1845
Fellow of the Society of Graphic Designers of Canada
Research Associate, New Brunswick Museum
Regional Coordinator, Atlantic Dragonfly Inventory Program
Coordinator, Maine Damselfly and Dragonfly Survey
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