Pick of the Week – Pretty Flies, Bad Apples

My work life is in entomology (bug stuff). Specifically, integrated pest management.

My personal life aims for sustainable, healthy, local living. So, when I found one of my favourite local foods being ravaged by an insect pest, I was all over it!

The sprawling crabapple tree in my former backyard produced so many healthy, mid-size, tasty crabs. I ate them raw, made applesauce, baked them, and still had barely touched the tree.

“Boy, a lot of fruit must go to waste in Edmonton,” I thought (and said). My boss told me about OFRE, and I haven’t looked back! That was 2011. The first pick I attended as a volunteer, the apple trees had apple maggot. What looked like large, normal apples on the tree were actually slimy and decayed, with tunnels inside. At the time, the organizers seemed to feel this was an anomaly, not the norm. “What is this dastardly bug ruining local apples?” I had to know.

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I learned that Rhagoletis pomonella is relatively new to Edmonton.  It was first recorded here about 10 years ago. It evolved as a new species from hawthorne maggot flies only a few hundred years ago in North America, after the introduction of apple trees. Now it has spread all over the continent.

The flies lay eggs on apples. The maggots (baby flies) eat tunnels and grow inside the fruit and then drop out to pupate in the soil under the tree. Next summer, they emerge as flies.

“Hmm. Neat. Thank goodness it’s not very common,” I thought upon learning all this.

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The next summer, I eagerly waited again for my yummy crabapples to be ready. I prefer them greener and crunchy, so I picked them fairly early and processed them right away: canning them, making apple butter etc… But the ones I left longer started looking ominously dimply. They had apple maggot!! Now my relationship with this fly was personal!

More and more apples were coming up maggoty. I started wondering what could be done. On my own time, as well as in my work with the City of Edmonton, I’ve been doing some research and observing maggoty apples. These are a few of the things I’ve learned:

1) Apple Maggot Flies are Pretty! With a very distinctive black wing pattern and iridescent red/blue eyes, I find these guys pretty endearing (just me?). This is a struggle shared by many entomologists: Dislike the pest’s action/admire the pest!

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2) Maggots Don’t Wait Until the Apples Hit the Ground. In all the literature, it says the maggots go into the ground from apples that have fallen down. But I have definitely had maggots raining on me while sleeping under my apple tree. So if you want to reduce the flies for the following year, you can’t wait until the apples fall to dispose of them.

3) Getting Rid of Apple Maggot is Not Easy. The biggest challenge of getting rid of these flies is that even if you do everything right as a tree owner (pick all apples and send to landfill, put out sticky traps, cover the ground under the tree from June through July etc), if a neighbour (in a 1km radius) doesn’t do their part, their flies may still find your apples and re-infect your tree.

Orchard owners can just spray all of their trees, eliminating the pest. But spraying is not feasible for a homeowner as effective sprays are not available for private use. As well, timing is very important, and repeated spraying is needed. So one has to rely on the participation of all his neighbours to “cure” a tree.

4) You can Save Some of Your Apples. Some orchards and individuals place a nylon or plastic bag around each apple when they are small. The fruit grows inside the bag, untouched by flies, and therefore, maggot-free! This is not something I am willing to do. So I tried what I have named “Maggot Exclusion Sleeves”. Basically, I made socks for entire branches by glue-gunning white garden netting into tube shapes. So, I enclosed all the apples on several branches, and had 100% success at protecting the enclosed ones from apple maggot! Online, you can also get giant nets meant to cover the entire tree! More expensive, but hey, your apples are protected.

5) There are Natural Biocontrols in Edmonton. I reared a bunch of flies from apple maggots and found that from some of the pupae came parasitoid wasps! This is exciting, as it shows that there are insects here that are helping reduce fly numbers. One of the downsides of using the recommended yellow sticky traps is that the wasps feed on flowers as adults and so are also attracted and stick to them.

Can we get rid of apple maggot in Edmonton? Sheesh. I dunno. It’s daunting. But, it would save so many delicious, local apples if we could.

The more that people know about the value of their apples, and understand how apple maggot works, the better chance there is they will act to eliminate these pretty but pesky flies. So through OFRE and the City lab I hope to work on public outreach and education.

Do you have apple maggot?

You can direct any apple maggot questions to: healthyfruit@operationfruitrescue.org.

I would also like to rear as many maggots as possible, to get a better idea of how much parasitism is going on. If you have maggots in your apples and are willing to share them, please contact me at healthyfruit@operationfruitrescue.org.

Happy fruit season!

Sarah McPike

Credits: All photos from Prevention and Management of Apple Maggot in Commercial Apple Orchards in British Columbia

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