Mites and how to avoid them

Mites - what they look like

MiteThe biggest threat to Drosophila culture is mite infestation. While some mite species only share the flies' food, others eat fly embryos and pupae and can eventually wipe out a fly lab. Even ‘food mites' can increase in number so rapidly (often by parthenogenesis) that they can destroy fly stocks. Adult mites are smaller than a Drosophila embryo, so can be difficult to detect. In older Drosophila cultures, they will normally be found wandering around the empty pupal cases. Mite embryos are even tinier and are often found in pearly strands of 10-20 eggs between Drosophila pupae.

In the video below (between 0.45 and 1.50),a single adult mite is seen walking through a Drosophila culture before pausing at a pupal case. You can see how small the mite is compared to the passing flies and the pupa itself. 

Mites - how to control them

Mites are everywhere, so constant vigilance is required to keep Drosophila cultures 'mite free'. These three precautions are the most effective for controlling mites:

  1. Quarantine all incoming Drosophila stocks. Any new stocks that enter the lab need to be kept isolated from the main stocks for at least 2 full generations (see full quarantine procedure here).
  2. Transfer fly stocks regularly. The life cycles of most mite species that infect Drosophila cultures are a little longer than that of the fly. If the flies are transferred soon after they eclose, the mites will not have completed their life cycle and so should not be able to overwhelm the stock.
  3. Keep the fly lab spotlessly clean. Mite species thrive on the detritus that accumulates in fly incubators and around working areas in the fly lab. It is important to clean/wash all equipment that comes into contact with flies and fly cultures. Mites and their eggs can be killed by ethanol, so wiping down your microscope, bench, CO2 pad and brushes with ethanol before and/or after you handle your flies is recommended.

Help! I've got mites.

It is not a sin to find mites in your fly stocks, but it is a sin to do nothing about it. If you discover mites in one of your stocks you should:

  1. Immediately remove the infected vial from the lab, seal it in an autoclave bag and arrange for it to be autoclaved as soon as possible. Closely monitor all fly vials that were kept close to the infected vial, and discard any that also become infected.
  2. Wipe down everything that has come into contact with the infected vial with ethanol. This includes the container the flies were kept in, the area where you worked with the flies and any tools you used to work with the flies.
  3. Inform the Fly Facility staff, we need to know.
If your mite-infested fly stock is irreplaceable, you can attempt to rescue it. This must be done in the fly isolation/quarantine area.
  1. Select ~5 pairs of flies that don't appear to be carrying mites or mite eggs and place them in a clean vial. 
  2. Transfer the flies to new food 3 times, once every 2 days, and keep only the last vial. 
  3. Monitor the rescued stock for at least 2 full generations (follow the quarantine procedures described here) to ensure that it is mite-free. 
IMPORTANT: If you are unsure what mites look like or would like confirmation that your cultures are mite-free, please ask a member of the Fly Facility staff or some other experienced fly worker.