Almost all people that use Drosophila (aka Fly Pushers) spend an inordinate amount of time sitting at a dissecting microscope and sorting anesthetized flies. In my lab we do combine two types of experiments that require what feels like an insane amount of flies: memory experiments and biochemistry experiments. That is, we perform biochemistry and molecular biology experiments on flies to understand the mechanisms of memory formation and how alcohol and drugs of abuse influence this. In order words, we collect a lot of flies (we’re talking easily thousands and up to tens of thousands per day for some experiments). And we sort a lot of flies because we separate out male and female flies for each experiment, and often have to select against a balancer to make sure we have the right genetic components in each fly.
So, what are the best tools for fly pushing? I’ll address anesthesia and behavior in another post. Here I would like to address what to use to collect and sort flies. Throughout my career, I’ve also worked with both brushes and feathers, so I have, what I think, are well informed opinions:
Brushes should be used for all larval collection. Not the stubby little brushes or the older brushes with the stray bristles, but the nice, expensive, small, fancy-art-store brushes with soft, tapered bristles about 1 cm in length. They are great for gently separating out larvae in soft food, and strong enough to break through hard food to gently wisk the larvae into a small dish for a gentle wash.
Brushes can be used for adult fly collection, but I’d only recommend this for small amounts flies. Like if you only need a few flies from a small handful of vials. Because, make no mistake here, collecting flies with brushes is slower than collecting flies with feathers.
Feathers are better for pushing large amounts of flies. But the type of feather and how it is cut is very important! Feathers are faster because: they have a large surface for swiping groups of flies, they have a thin surface for dividing flies into groups, and they have a soft tip for rotating and turning individual flies so you can see the phenotypes you need to see.
What type of feather should you use? This is largely attributed to individual preferences. I like the look of the feathers that fall off my budgies when they molt because of the pretty colors (I mean, how wonderful to have the whimsy of a splash of color when doing my morning fly collection!), but they are a bit thin. Pigeon feathers and seagull feathers work OK if they are high enough quality. But if I’m being honest, duck feathers probably work the best. And not just ANY duck feathers, but the feathers from a duck that was hunted and plucked many years ago for Todd Laverty, who was a long-time lab manager of Gerry Rubin and then ran the Janelia FlyCore until he retired. We were lucky enough to get a bag of those feathers when Todd retired, and it gives me such joy to have these good-luck feathers (and history) in my lab.
How you prepare your feather is also very important and attributed to individual preference. It will be different if you are left or right handed. I like to have a feather with a soft tip and the concave side of the curve facing me as I fly push. I also like the bottom vane larger than the top vane.
The worst thing EVER is when the shaft on your favorite feather breaks and the vane gets a split. The nice thing about feathers is if you gently press the vane back together, you can sometimes get another month or so out of it. Which will give you enough time to get a new feather and slowly adjust to it.
Some people also aspirate their flies to collect them. Like suck them up and move them around on the pad with a fly aspirator (aka pooter). Emily Petruccelli, a previous postdoc in my lab, used to do this and she was really fast. She was also able to sort and sex flies this way without even looking into the scope - just looking at the flies on the pad. But it always made me worry that sucking in this extra little bit of CO2 would give her a headache, so I personally wouldn’t recommend that.
I suspect you experienced fly people out there also have OPINIONS, and I’d love to hear them!