Bloomington Fly Food Prep Method
Updated March 30, 2007
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This method was developed at Bloomington to support high-throughput media preparation. Trays of fresh vials are sealed with Press’n Seal® plastic wrap instead of plugs. This material is easy to handle, quick to apply, and relatively inexpensive. Vials sealed in this way stay moist much longer than plugged vials. Press’n Seal® can be purchased from Genesee Scientific or your local grocery store.

This is our new method:

Glassware is racked by hand in cardboard trays with dividers that hold 100 vials in a 10 x 10 array. 80 trays can be racked in ~2.5 hours (this step can be eliminated by using pre-racked plastic vials).

Trays of vials are filled with medium using the Applied Scientific media filler (Fisher, AS-770) and a heavy duty peristaltic pump (Watson-Marlow Bredel 624Di/L) to keep the filler filled. Uniform delivery from the filler requires that the food be uniformly hot and at a consistent volume, so a pump powerful enough to quickly deliver a liter of food is very helpful. We start with four liters of food in the filler and use a pump program that delivers a liter of food in a few seconds and pauses for 20 seconds. This allows a tray to be filled, covered (we use cotton bandanas) and placed on the cooling rack every 25 seconds or so. The pump can be stopped with a foot peddle if a longer pause is needed, but the filler can’t be left for long because delivery becomes uneven as the food cools. 80 liters of food can be dispensed into vials (~10 ml per vial) in less than 45 minutes (vs 3 hrs 45 minutes dispensing one vial at a time with our National Instruments AB-5).

Trays are left to cool for at least 2 hours. Condensation is slow to evaporate with this method; vials sealed while still too warm will be wet. When the food is cool, each tray of vials is covered with a sheet of Press’n Seal®. A piece long enough to cover the vials is torn off, laid on top of the vials tacky-side down, and briefly rubbed with the flat of the hand to seal the plastic to the tops of the vials. Another cardboard tray (without the dividers) is then inverted onto the sealed vials. This lid makes the vials easy to handle without disturbing the plastic. It takes a little over an hour to seal, date and stack 80 trays of vials, compared to 8 to 10 hours to plug with rayon.

A drawback is that any small gaps in the seal, from wrinkles in the plastic or small differences in the height of vials (as with glass) will allow flies to enter if food is held outside a cold room. This problem can be solved by the end user checking and correcting the seal as needed when a tray is removed from the cold room, or by placing trays that will be left at room temperature in a sealed plastic bag (16" x 16" slide lock bag is a good size for narrow vials).

We invert the trays for use (into a tray without a grid), so you don’t have to peel the plastic away, you just pull off one vial at a time (the cardboard grid holds the array in place). Others in the Bloomington fly group prefer to use them right side up and they slice the wrap between rows with a razor blade before use so that the wrap can be peeled from one or two vials at a time without disturbing others.