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Aphids, Fungus Gnats, & Fruit Flies

Originally published at The Suburban Garden. Please leave any comments there.

Aphids feasting on a hot pepper plant.

Aphids feasting on a hot pepper plant.

I’ve been hearing the same questions over and over, and thought perhaps it was time to do a post about common household pests.  I’ve written a post about aphids in the past, and this post will include all of that information, as well as information on fungus gnats and fruit flies.

Before getting into the nitty-gritty about each pest, it’s important to differentiate between the three in terms of appearance, so that you know what you are dealing with.  Aphids are tiny white flies, and their larvae has small, clear-green bodies.  Fungus gnats are tiny, slow moving black flies, and their larvae is a clear-brown colour.  Fruit flies are tiny, quick moving black flies, and their larvae is a clear-yellowy-brown colour, similar to maggots (only smaller).

This article will provide information and suggestions on how to rid your plants and homes of each of these three common pests.



Aphid Overview
Aphids are tiny white flies that start as a clear-green larvae.  They have soft bodies, and their mouths, called “stylets”, are designed so that they can suck their food in.  Most aphids also have abdominal tubes through which they can secret a thick, quick-hardening defensive fluid called “cornicle wax”.  This is the sticky whitish fluid you’ll often see on your  plants when you find aphids.

Most species of aphids are monophagous, which means that they feed only on one plant species.  This would explain why you might find them crawling all over one variety of plant, but leave all of the other plants alone.

Aphids feed on the sap from phloam vessels in plants (the tissue that carries all of the nutrients through the plant).  Through pressure, the sap is forced into the mouths of the aphids, requiring little to no effort on the part of the pest.  Occasionally they will ingest Xylem sap, which has more sugars and requires more sucking to ingest.

Natural Predators to Aphids
Aphids have a variety of natural predators, many of which can be introduced into a garden setting to help control the aphid population (or irradicate them entirely).  These include:  ladybugshoverfliesparasitic wasps, and lacewings.

There are also a variety of bacteria and fungi.  The aphids brush against the spores of the fungi and, after about three days, the fungi pierces the aphids from the inside and they die.  Later the fungus releases more spores into the air.

Aphids can also be killed off by freezing or extreme high temperatures.

Getting Rid of Aphids
Due to their soft bodies and lack of personal defenses against pressure, a strong spray of water from a hose every few days is usually enough to keep aphids off of your plants.  If you’re indoors, you can also simply rub your fingers along the stronger leaves to and gently squeeze the aphids, killing them instantly.

You can opt to import insects such as ladybugs into your garden.  These are often found at plant nurseries, or can be ordered online.If you are not able to obtain natural predators, or you are dealing with plants sensitive to water pressure, neem oil can be applied to the plants.  A homemade concoction which is currently popular is:

  • 1 tablespoon of dish soap
  • 1 tablespoon vegetable oil
  • 700ml water
Place all ingredients in a spray bottle, shake, and spray.  If you are able to use a strong stream on the plants, this will help remove the aphid larvae.  If you are only able to use a light mist on a delicate plant, the oil helps the soap stick to the aphids, which envelopes them and basically drowns them.



Fungus Gnat Overview
Fungus gnats are tiny black flies, with clear-brown larvae.  Fungus gnats are usually found in the top 2-3 inches of growing medium, and feast on the fungus, algae, and roots under the soil.  The larvae will also eat rotting plant matter on top of the soil.  The gnats are fully grown in 2-3 weeks, and lay up to 200 eggs in the soil.

Fungus gnat infestations can be detected by simply placing slices of potato into the growing medium.  The potato attracts the gnats (which feed on it).  After a few days, turn the potato slices over to see larvae underneath them.

Natural Predators to Fungus Gnats
The most common natural predator to fungus gnats are nematodes.

Getting Rid of Fungus Gnats
Fungus gnats are attracted to moist soil.  Allowing the soil to dry out between watering, and avoiding over-watering, are very effective methods in killing most of them.  Removing any dried or dead plant matter from the surface of the soil will also help.

Adding a layer of sterile sand (about 1/2 inch) on top of the soil will help keep the larvae from escaping, and will keep the adults from reaching the soil.

A long-term control method is to use yellow sticky card traps*. Fungus gnats are attracted to the yellow stickies because, to the gnats, the traps mimic healthy leaves.  Since the adults get stuck to the cards, they aren’t able to lay their eggs in the soil.  Place the cards in the soil, or hang them from the leaves of larger plants.  Since the gnats often head towards windows, it is helpful to place one near the top of a window frame.

If the problem persists, there are a number of houseplant insecticides available as well, including granules, sprays, and spikes, which can often be found in the pest-control section of local plant nurseries or garden centres.

*I’ve personally captured literally THOUSANDS of gnats with the sticky cards over time.  Warning:  be careful where you place the traps if you have pets, they can be quite painful to remove from a furry friend.  The cards should also not be used outdoors, as they could stick to, and cause harm to, furry or feathered animals.



Fruit Fly Overview
Fruit flies are tiny, quick moving black flies, and their larvae is a clear-yellowy-brown colour, similar to maggots (only smaller).  While they are less of a problem with plants, they are just as big of a nuisance.  Fruit flies feast on fermenting fruit, and can detect it from very far away.

Fruit flies usually enter your home by hitching a ride on fruits and vegetables, or even outside plants.  Fruit flies are so small that they can also penetrate window screens.  Therefore, if you have fruit somewhere in your home, there are likely fruit flies trying to find a way in.  These pests live for about 30 days, and breed quickly, laying eggs on fermenting fruit.

Natural Predators to Fruit Flies / Outdoor Fruit Fly Control
Unfortunately, most natural enemies of the fruit fly are not ones you would want in your home.  That said, if you have fruit trees, this information may be useful to you.

Natural predators to the fruit fly include weaver ants, parasitic wasps, rove beetles, spiders, bats, and birds.

Evaluate your crops twice a week, removing and discarding fruits that are overripe immediately.  The maggots can be killed by placing the fruits in black bags and leaving them in the sun for a few hours.  Alternatively, you can bury the fruits at least 2 feet deep to keep the adults from emerging from the soil.  Harvesting crops early also helps keep the fruit flies from becoming attracted to the fruits.

Fruit flies can be kept away from tree fruit by placing an exclusion bag around the branches of the fruiting tree.  The bag should allow light and air to reach the fruit, while keeping the flies from reaching it.

Organic fruit fly sprays are also available, and can be purchased from nurseries and garden centres.

Getting Rid of Fruit Flies
Once you have a few fruit flies, you’ll want to get rid of them ASAP, before they get a chance to breed.

Create a common (and tested) homemade trap by placing a piece of overripe, skinless fruit in a bowl, adding some balsamic vinegar or wine, and covering the bowl tightly with plastic wrap.  Pierce small holes in the plastic wrap with a fork.  Place the concoction near the bowl of fruit that the flies are attracted to.  The flies will go for the fermenting fruit instead of the fresh fruit, and will become trapped in the bowl (some will drown in the liquid).

Placing a piece of fruit in a zip-lock bag and leaving the bag open about an inch is also effective at trapping the pests.  Once they’re trapped, simply close the bag and discard the entire trap, fruit and all.

If you aren’t up for a DIY project, a great store-bought trap like this one works well.  We tried this particular model, and a single trap cleared 200+ fruit flies in less than 24 hours.

Maintaining The Removal of Fruit Flies
Removing all sources of fruit from your home will go a long way to keeping away the pests.  If they can’t smell nourishment, they will go elsewhere in search of food.  Cleaning your fruits and vegetables before bringing them into the house will also help – fruit flies often find their way indoors by hitching a ride on produce, either from the garden or from the grocery store.

Store fruits and vegetables in the fridge, if possible.  Store food that can not be refrigerated in a bowl with a cover on it.

Rinse out fruit juice containers and put them in outdoor recycle bins.  The fruit flies aren’t only attracted to the fruits, they’re also attracted to fruit juices.

Get rid of overripe fruits and vegetables immediately, and empty kitchen composters regularly.  The kitchen composter, containing primarily rotting food, is a haven for fruit flies.