// Twitter Cards // Prexisting Head The Biologist Is In: Doom of the Fruit Fly

Tuesday, January 5, 2016

Doom of the Fruit Fly

The red-eyed fruit-fly familiar to biology students everywhere (Drosophila melanogastor) likes to lay eggs in recently spoiled fruit, where its larvae can consume the fruit sugars and the yeasts that grow on them. If you have an infestation of D. melanogastor in your kitchen, the first step is to get rid of whatever they're breeding in. The second step is to get rid of all the adults that are flying around. You could spray some poison, get skilled with a fly-swatter, or buy some commercial traps... but it is a pretty simple task to make your own trap without needing any poison. Make a paper cone with a small hole in the tip, then put it point-down into small jar with a bit of over-ripe fruit in the bottom as bait

The inverted cone prevents the fruit flies from finding their way out once they've crawled inside. If you don't have an inverted cone, you'll just be breeding more fruit flies to infest your kitchen. The bait can be whatever rotten fruit was attracting the flies.

One species of fruit-flies that doesn't like recently spoiled fruit is the Spotted-Wing Fruit Fly (Drosophila suzukii). This species lays its eggs in ripe soft fruit (raspberries, strawberries, blueberries, etc.). They are able to do this because the females have a saw-edged ovipositor that lets them cut into soft fruit to lay their eggs. They don't have to wait for fruit to begin rotting like the typical fruit flies and their infestation will result in the rapid destruction of fruit that would otherwise go to market. This has become a big problem for people trying to grow berries without pesticides. There are traps for these flies, but they're only really useful as a surveillance tool. The traps alone will not protect your fruit.

Image from blogs.cornell.edu post.
Another group of fruit-flies that don't like recently spoiled fruit are the dark-eyed fruit flies. D. repleta, D. hydei, and D. robusta are slightly larger and prefer their food source to be far more degraded. What this often means is the grimy collection of goo in floor drains or between/underneath cracked floor tiles in restaurant kitchens. It also can mean chicken poop in a barn, a mostly rotted compost pile, or the litter of a reptile tank (that I really probably should have cleaned already).

Once I noticed the existence of the flies, I cleaned up the source of the problem and my gecko is happy with her spiffy new home. The fruit-fly trap I described for D. melanogastor would work equally well for these flies if I could figure out a bait that they would be attracted to. I could scoop some of the old rotted reptile media into the jar, but I discovered something a bit more interesting (and effective).

S. integrifolium "Pumpkin Tree" fruit.
I had the branches and fruit from a Solanum integrifolium "Pumpkin Tree" plant I grew this year hanging up in our kitchen to dry. I first noticed the dark-eyed fruit-flies because they were hanging out on the branches when I checked on how the dry the fruit was. As an experiment, I put a couple of the fruit into the previously described fruit-fly trap and put the remainder of the plant outside.

The next morning, all of the flies from the kitchen were having a party -inside- the trap. I scattered all the flies outside and reset the trap beside the (now clean) reptile tank. The next morning, all the fruit-flies in that area were also inside the trap. The dark-eyed fruit-flies (of whichever species I have here; D. repleta, D. hydei, or D. robusta) really, really, love the fruit of the "Pumpkin Tree" plant.

I've dehydrated and powdered the remaining fruit to save them for later use as a bait. If the dark-eyed fruit-flies ever reappear, I'll mix some of the powder with some water as bait and continue the experiment. I could also do some experiments outside next summer, as the dark-eyed fruit flies are likely to prosper in my compost pile again.

I've saved seeds from the "Pumpkin Tree" plant and will definitely be growing it again for its decorative and fly-trapping features.