FRUIT FLY BULLETIN #5 WESTERN CHERRY FRUIT FLY (CFF)

We have already written extensively about the Spotted Wing Drosophila (SWD) which hosts on
our cherries as well as many other soft-skinned fruits and berries.

However, today I will write about the Western Cherry Fruit Fly (CFF for short), which we
suspect is also in Powell River. So this bulletin is particularly addressed to everyone who has a
cherry tree or trees – or who has a neighbour with cherry trees.

One of our important tasks early this coming summer is going to be to get a positive identification one way or the other on CFF.

What is CFF?

Its name is Rhagoletis indifferens, a fruit fly native to North America. It has been widespread in
North America for a century – but not suspected here until last year. It is a true fruit fly, unlike
the SWD which is a species of drosophila (commonly called a vinegar fly).
CFF is about the size of a small house fly, with distinctive striped wings.

It hosts only on cherries, but on all kinds of cherries – sweet, sour, and wild. It has only one breeding cycle per summer which might make it a little easier to combat than the SWD.
Each female can lay 50 –200 eggs over a three-week period, depending on temperature conditions.

Once the skin of a ripening cherry is soft enough, at the pink/salmon stage, the female CFF can
pierce the skin and deposit several eggs. The eggs hatch in about a week and the larvae feed
inside the cherry for two to three weeks. Then they bore an exit hole to crawl out and drop to the
ground under the tree. There they burrow down a couple of inches and pupate until the next
summer.

Western cherry fruit fly adult on cherry
with larval exit holes

It is difficult to determine if cherries are infested until the larvae exit through the holes, or the
fruit is cut to reveal the larvae inside. You can understand how easy it would be to ‘give away’
or sell infested fruit without knowing it, and thus cause the spread of CFF.

What signs of CFF have we found in Powell River?

Last summer it was late July when we got our first alert that there were grubs in cherries. A lot
of this damage was done for sure by SWD. However one grower in Wildwood not only got
specimens of a couple of cherries with exit holes but actually saw a grub crawl out of a cherry
and drop to the ground. This is CFF behaviour and not SWD behaviour. But it was too late to
catch a fly for positive identification.

I got many reports of grubs in cherries all over Powell River district, but we do not know which
kind of grubs. Remember that SWD also attack cherries. There were also a number of reports of
cherries not only rotting on the tree, but also of cherries falling into an unusual sticky mess under
the tree. Again, we do not know which fruit fly would have caused this.

How far do CFF spread?

It is thought that CFF do not travel very far once they have host fruit available. But within that
area they may infest fruit heavily. If we can determine this May/June if they are here, and where
they are, we can take measures to contain them and try to get on top of them. The only evidence
so far - the exit holes - came from one site in Wildwood.

What can I do now in spring?

1. If you also remember seeing exit holes in your cherries please let me know right away. If we
can map where they are, we can concentrate our efforts.
2. Practise good garden hygiene, just as for the SWD and other pests.
3. Start getting large cherry trees down to a size where you can pick the whole crop.
4. Just as with SWD, we have to ‘pick early, pick often, pick clean’. Any fruit left on the tree
provides a breeding ground for more CFF (and SWD) for next year.

What can I do if I think I may have had CFF in my cherries last year?

Any CFF pupae are now over-wintering in the ground under the cherry tree.
The flies will start to emerge when the weather warms up, mid-May give or take a week or two, and continue to emerge all through the fruit season.

By early May, you could cover the ground under your tree from drip-line to trunk with heavy landscape cloth or black plastic to block the adult flies from emerging. Fix the edges down well so the ground cover stays in place.
Later, in the fruit season, this ground cover will similarly prevent the larvae from burrowing into the soil. (That is a good time to let your chickens run around under the tree too, if you have chickens.)

What to do in summer?
My first concern will be to get specimens of the adult fly to send to the entomologist for a
positive ID. I will write again before May about setting out a trap, and about controls.

More info re CFF - from BC Ministry of Agriculture and Utah State University. Both articles are very helpful and will give you a lot more information. (But don’task me about the ‘degree days’ chart in the Utah article. Maybe one of you can work it out!)

Related pests, other rhagoletis:
When you read these articles, you’ll see that there are several other related rhagoletis fruit flies.
- The Currant Fruit Fly is in Powell River and has been here for some time; it hosts on currants
and gooseberries.
- The Apple Maggot Fly is on Vancouver Island and may be here. Its larvae eat the flesh of the
apple and cause it to rot on the tree. It is different from the Codling Moth whose larvae go to the
core of the apple and don’t usually cause it to rot.
- The Walnut Husk Fly. . . I don’t know about.
More later on,
Margaret Cooper