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So long as there is only one fly in the tube, the genitalia shouldn't get lost. I make a note in the record book and put an extra label in the tube to remind me that the genitalia are loose in the tube.

Another option is to mount the genitalia on card so they can be pinned, although they are then separate from the rest of the specimen. There is a substance called Dimethyl Hydantoin Formaldehyde or DMHF that the coleopterists use for mounting beetle genitalia. You buy it as a white crystal and dissolve it 50/50 in water to produce a clear treacle. With a pinhead you put a tiny spot on a piece of card and then place the genitalia in. The genitalia need to be wet so that they don't contain air bubbles and float, but not too wet so that they don't dilute the DMHF. I take them out the alcohol, just touch them on to tissue paper so that 90% of the liquid is sucked off by capillary action, then put the genitalia into the DMHF. You then have about a minute or two to manoeuvre the genitalia with pins into the position you want them, after which the DMHF gets too stiff. It soon sets to give a clear hard protective capsule over the genitalia, with excellent optical properties. If in the future the DMHF gets cracked or scratched or you really need a different view, the DMHF can be redissolved in alcohol and the genitalia extracted. Or if you expose DMHF to fumes of ethyl acetate, it just vanishes into the air leaving the genitalia exposed on the card.

The biggest problem with DMHF is how to get some. Apparently it is a component in hair spray. You could buy it by the kilo but that is very expensive when 5 mls would be enough to last most amateurs a lifetime. But it seems to be very difficult to find for sale in any quantity these days, so if any Diptera.info members find a source, please let us know. However, this recent mailing on the British beetles e-mail group may offer an alternative:

?Entomologist (and retired chemist) Juan De Ferrer who lives in Algeciras, Spain, has recently been selling small (c. 20 ml) bottles of "improved PVP" solution to EU countries, except the UK, for about 4 Euros each. PVP is very slightly amber in colour but is otherwise identical to DMHF (The Coleopterist 14: 29-35}.?

Unfortunately, no contact details for Juan de Ferrer were given. Perhaps one of our Spanish correspondents knows him? I don?t know what PVP stands for.

John Bratton