All Drosophila species, including D mel, do much better when
vegetable (powdered spinach for example) is added to the
medium. Part of the reason is the additional vitamins this
provideds - conventional medium is low in available
vitamins. Obscura group species will certainly benefit.
Conventional medium is also far too rich in carbohydrate,
particularly sugar, which favours fermenting yeasts against
other microrganisms and i suspect, though i havn't tried,
that sugarless medium with cooked vegetable and/or fungus
(mushroom) might suit obscura more. I'd love to have this
tested but who'd fund such a 'boring' study ?
For conventional lab. rearing living food is problematic but
if you're having real problems then try inocculating the
medium with microrganisms from the substrate the flies were
originally reared from.
University of Leeds, Yorkshire
England, LS2 9JT UK
a.j.davis at uk.ac.leeds