Firstly there was nothing wrong with the seeds themselves, they germinated well (after vernalising) and grew on fairly well into the autumn, but when I came to have a look at them now (northern hemisphere - so it's springtime, and time to start the seedling/bulblets into growth) for some species there are very very few. To cut a long story short - are they particularly susceptible to sciarid flies (fungus gnats) ?
I sowed several varieties and they all germinated very well except for a couple of late germinators (mentioned in another post - and are now doing well) and most are now starting to show some growth. I've had the seed trays in separate propagators (plastic base and transparent lid), two or three trays to a propagator and this one propagator has done very badly; the propagators are all together so differences in temperature and watering are minimal. However I did notice a few sciarid flies in the autumn and sprayed with a pyrethrum based insecticide which seemed to work (this year I've bought some 'Gnat Off' and given one application already). I used some copper-based fungicide once or twice early on but everything did seem quite normal although I did wonder whether this particular propagator's seedlings may have died back in the autumn a little earlier than the others. I did let the trays dry off but tried to keep a little moisture just in case. The winter temperatures have been fairly mild - a few days sub-zero and a good number of overnight frosts but I have kept the seedlings slightly heated (when necessary) and they probably haven't been below zero at all.
So bearing in mind that the flies' damage is really done under the soil and so I probably didn't notice - and didn't properly check - they seem to be the most likely cause.
Anyone else noticed a particular problem with the flies ? Or any other suggestions ?