[Odonata-l] Emergence Triggers

[Hal White]

Paul and others,

I really would be careful trying to make conclusions about the factors 
critical for emergence from nymphs kept inside during the winter in 
uncontrolled circumstances. Anecdotally, I too have had emergence much 
earlier than in the field. The temperatures were different for a long 
time and the photoperiods were quite different as well. Also water 
temperatures where the larva live are less variable and slower to 
respond than air temperature.

Corbet is an excellent place to start for anyone wishing to study this 
issue systematically for particular species. Clearly, there are many 
interesting issues about Odonate biology that warrant further study.

Hal


Paul Brunelle wrote:
> 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
> -----------------------------------------------------------------------------------
> *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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