We're having difficulty getting eggs "on demand" from D. virilis
and D. hydei. We've tried starving them overnight for one night, or
starving them for 2 nights, allowing the flies to feed for about
1 hour after the 1st night. (We'll try to see now if they lay their
eggs late at night and adjust our timer accordingly.) We are using
Carolina Biological blue media mixed with grape juice and smudged with
a paste of yeast to induce egg-laying. We'd appreciate any
suggestions you may have to offer.