1. Label seeded plates with strain name and date. Always label the bottom of the plate, at the edges. Use strain number or allele designation(s) for absolute unambiguity as to strain identity. For plates that may be shared, it may be appropriate to include your initials along with the date.
Note: it is also a good idea to label the lid with some uniquely identifying code that can be matched with the bottom of the plate. Thus when plates are dropped, which inevitably happens, appropriate lids can be matched up with plates, avoiding possible cross-contamination.
2. Dip the wide, blunt end of a spatula in 125 ml flask of ethanol (keep a reasonable distance from lighted flame source). Keep end about level, pointing slightly down to avoid ethanol running on to hand.
3. Pass spatula through flame just long enough to light. (Do not keep in flame source.) Watch out for flaming drips.
4. Cut a rectangular chunk from old plate about 1 x 2 cm. You may want to check in dissecting 'scope for a region with live worms if the plate is old or sparse. Lift out of old plate with spatula.
5. Place chunk in new plate, near the edge, worm-side down. Slide chunk slightly to spread worms on new plate. Confirm transfer under dissecting 'scope.
6. Return plates to incubator. Keep original plate as backup. Typically you may then discard the last generation chunked plate.