Raising syrphid larvae

Those of you raising aphid eating syrphid maggots may find the excerpts from this series of e-mails circulated by the Syrphidae list serve informative. I am sure that this applies to American species just as well as British ones.
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Sent: Sunday, June 27, 2010 8:28 AM
To: syrphidae@lists.nottingham.ac.uk
Subject: [Syrphidae] Raising Syrphus larvae
Good afternoon,
I could do with some advice on my hoverflies!
I am raising Syrphus ribesii larvae and am keeping each larvae individually in small glass / plastic test tubes and provide them with a small leaf and lots of fresh aphids every day. I clean the tubes every day, and use damp cotton wool to plug the ends of the tube. They are kept at 70% humidity, 16:8 hours light: dark.
1. My larvae are now 6 days old and I need to know if they have any requirements for successful development into pupae - do they require something to stick too or do they need to hang upside down etc. Also should I need to keep them moist throughout their pupae stage?
2. I have recently had many (less than 25%) of different age classes turn black and die. It appears on first glance like they have not discharged their gut... but I have no idea. Does anyone recognise these symptoms or could provide advice or keeping more alive?
Thanks,
Matt Perkins
PhD Researcher
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Sent: 27 June 2010 13:57
To: 'Hoverfly discussion list'
Subject: [Syrphidae] RE: Raising Syrphus larvae
Matt,
I have had this experience with larvae of Heringia calcarata. It has been sporadic and unpredictable, but like you, I would be interested to know if anyone has an explanation.
Cheers - Chris
Chris Bergh
Associate Professor of Entomology
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Dear Matt (& Chris), Re your queries about rearing aphidophagous larvae, I have reared many species over the years. Under the rearing conditions Matt describes, you shouldn’t have any particular problems.
However, I know well the dead ‘blackened’ larvae you have encountered. Some mortality is to be expected in cultures and there is nothing special you can do to prevent it, other than carrying on and hoping the proportion dying remains small. The main dangers to larvae in culture are desiccation and the quality and quantity of prey. Use of damp cotton wool plugs should ensure there is enough (& not too much) moisture in your tubes and providing small to medium sized aphids until larvae have reached the 3rd stage when they will take a wider range of prey sizes, should be OK.
Not all aphid species are suitable even for a polyphagous species like S. ribesii, and although you don’t mention what aphid species you are offering, I assume that is something you are aware of. Also switching between aphid species presented as prey can sometimes cause mortality and should be avoided. Larvae, especially small ones, are obviously more vulnerable and require care in handling, i.e. use a brush to move them about rather than tweezers or forceps.
After larvae have finished feeding and emptied the hind gut, they are best removed to clean tubes and gently wrapped in slightly moistened tissue paper. Tubes should be stored in cool, dark conditions. Depending on time of year, it will be 2-3 weeks before adults appear or larvae will aestivate for several weeks or hibernate for several months. The tissue paper should be replaced every few weeks to prevent fungal infection.
Hope this is helpful.
All best wishes,
Graham
Graham E Rotheray
National Museums Collection Centre