Rhagoletis: Western Cherry Fruit Fly etc

FRUIT FLY BULLETIN #7
May 10, 2014
CHERRIES, CURRANTS /GOOSEBERRIES AND APPLES:
DEALING WITH RHAGOLETIS FRUIT FLY

This bulletin will concentrate on the Western Cherry Fruit Fly (CFF) – rhagoletis indifferens -
and its rhagoletis relatives, the Currant Fruit Fly and the Apple Maggot Fly. These rhagoletis
species are all native to North America and have been known for a hundred years or more,
although their spread to different areas has varied.

These are all true fruit flies (unlike the Spotted Wing Drosophila [SWD] which is a
drosphila/vinegar fly). Rhagoletis do cause damage similar to SWD but only to specific fruits,
and their life cycles - and therefore control methods - are different from SWD. If we
understand the life cycle of rhagoletis, we have the key to control methods. What I discuss
about CFF can be applied to the others because of the commonalities.

Rhagoletis Species we are concerned with locally: 


• Western Cherry Fruit Fly (CFF ) – rhagoletis indifferens or rhagoletis cingulata –
hosts on cherries only, but all kinds – sweet and sour cherries, wild cherries. If it turns
out that CFF is indeed identified as being in Powell River, it has only arrived very
recently.
• Currant Fruit Fly – rhagoletis ribicola, sometimes also called euphranta canadensis -
hosts only on currants (red, white and black) and gooseberries. This has been been in
Powell River area for some time now.
• Apple Maggot Fly – rhagoletis pomonella – hosts on apples, crabapples and hawthorns
only. Has only arrived in the last few years on southern Vancouver Island so may be here
too.

Are CFF in Powell River? We think we found evidence of their activity last year but we did not
get a specimen of the fly to do a positive identification. I will be working with a few gardeners
to try to get a specimen – or not - in June and July.

What are the signs of CFF attack on local cherries?
The Cherry Fruit Fly, like the SWD, lays eggs under the skin of ripening cherries, and the larvae feed inside the cherry and make it spoiled and wormy. But then the behaviour becomes different: the CFF grub chews an exit hole and drops to the ground under that tree. There is burrows down an inch or two and pupates until
the next summer. The distinctive clue to CFF presence is seeing the exit holes.

If you observe exit holes in your cherries – or saw exit holes last summer - please get in
touch with me and we will set out a trap and lure to try to get specimens.

Size and Appearance:
They are a little smaller than a house fly and each species has its own distinctive striped wing
pattern. (See link on CFF for wing diagrams to help you with identification of
each.) All these rhagoletis are bigger than SWD.

Life Cycle:
• CFF over-winter in the soil under the tree as pupae, not as adult flies. The adults will
begin to emerge as the weather warms up and the cherries begin to get a blush of colour
and the skins start to soften. This will be a bit later than the SWD - about early June,
depending on temperatures and fruit ripening. They will keep emerging in sequence right
through the period when there are ripe cherries available. Peak appearance often
coincides with peak harvest time.
• Upon emergence from the ground, the female fly undergoes a 7 – 10 day maturation
period before she mates and starts egg-laying. This is the time slot in which we can
try to stop them, with covers, sprays, getting picking, etc – before they lay the eggs.
Once eggs are laid, the larvae are virtually invulnerable – and destructive - inside the
fruit.
• The adult CFF lives 2 1/2 to 5 weeks, and each female can lay 50 – 200 eggs. They can
easily ruin an entire crop of a tree. However they do not fly far if they have a food
supply, so do not spread to other trees and properties as aggressively as SWD.
• Also, they complete only one breeding generation per summer . This makes control
easier than with the multi-generational SWD.

IF WE CAN INTERRUPT THE LIFE CYCLE AT THE PUPA OR FLY STAGE, WE CAN REDUCE THE INFESTATION NOT ONLY THIS YEAR, BUT NEXT YEAR TOO.

What can we do to control CFF?

1. Ground cover and Mulches
Cover the ground under the tree/bush from trunk to drip line to
(a) block the pupae from emerging, and
(b) to stop the larvae from burrowing into the soil after they have exited your cherries.
Landscape fabric, heavy black plastic or mill felt will all make a good barrier. Be sure that it is
firmly fixed down around the edges and trunk. They will still try to burrow in at the perimeter of
your ground cover, but at least you know where they are. Mulches of dense materials also can
prevent the larvae from burrowing in to complete their life cycle. One article even suggests that
growing grasses with very dense root systems under the tree make it hard for the larvae to
burrow in.
2. Good Harvest Methods
• Again, the rule is “pick early, pick often, pick clean. Store cool”.
• Start to pick cherries while they are still on the firm and pink side.
• Keep picking regularly as cherries ripen. At the end of the crop, pick the tree clean. This
is why it helps to have your tree down to a size you can manage.• Pick up all fallen fruit and fruit mush regularly. If you have put down ground cover, this
will also be a helpful in gathering all the fruit that falls.
• If fruits or culls are infested, burn/bake/boil, freeze or solarize them. Do not throw them
into the compost or over the back fence.
3. Chickens and birds
Invite them to eat the larvae as they drop down. Dig the soil up under your bush/tree or around
the perimeter of your ground cover to expose the pupae for the birds.
4. Nets and covers
Cherry trees are big to cover, but if you want to try this, read the Kootenay Kovers attachment
that I sent with Bulletin #6.
5. Traps?
• We will just use sticky traps with lures in targeted gardens to try to catch specimens for
ID and mapping purposes, and to know when/where/if they have appeared.
• There is no effective way to trap CFF for control.
• We advise against using sticky traps anyway because these catch many beneficial insects
and even humming birds and other small birds.
• Cider vinegar traps do not work with CFF because they are not vinegar flies.
6. Sprays
I am not going to get into much detail on sprays, but if anyone does choose to use them, note that
the time to stop the CFF from laying eggs is in that initial 7-10 day maturation period after
they emerge. Then spraying needs to be repeated at 7 – 14 day intervals right through the
harvest season to stop each successive emergence of flies, and should be continued beyond the
end of the harvest to destroy the late-emergers. The sprays used should be varied through the
season to avoid the CFF developing resistance. The spinosid group of sprays is considered
acceptable for organic certification. (Refer to the sprays chart in the attachment.)
Most of us will want to avoid using sprays. My entomologist adviser says that small growers
and backyard gardeners should be able to manage against the fruit flies that we face
without sprays, by using good garden hygiene and picking early, often and clean.
**************
ABOUT CURRANT FRUIT FLY
The adults lay eggs in young green fruit of currants and gooseberries. The larvae feed inside the
fruit, and infested fruit turns red and falls prematurely. The larvae exit the fallen berries, then
pupate and overwinter in the soil. Rake up fallen berries to reduce pest pressure. Lightly
cultivate the soil beneath the bushes to expose the pupae and larvae to predators.As they pupate under the bush, ground cover is a good protection. Nets and covers would also
be easier to use because the bushes are smaller.
Here is what an expert near Victoria wrote me about covering her currants:
I have sewed big bags that fit my red currants and just cover them from May 1 to June 10th or
so--tie bag securely around base of trunk so they can't get in to lay egg. Uncover for the rest of
the season since they are not laying eggs later. When I used curtain material I tried to limit
covering time to 3 weeks because it didn't let in enough light so was monitoring eggs being laid
in fruit. But if you use ProtekNet fabric, it lets in enough light and is sturdy enough not to snag
on branches.
******************
ABOUT APPLE MAGGOT FLY
Codling moth damage can be confused with apple maggot damage. The difference is codling
moth feeds in the core and the apple maggot tunnels throughout the flesh. The apple maggot will
lay its eggs under the skin of the fruit. When the eggs hatch the larva will wind their way
through the fruit and will typically stay there until the fruit drops. That’s when the larva will exit
the fruit and over-winter in pupa state in the soil
Apple maggot was first detected in the Fraser Valley of British Columbia in 2006. As of 2013
apple maggot had yet to be detected in the fruit production areas of Interior B.C..
To help prevent the spread of apple maggot to other parts of B.C., there are restrictions if you are
planning to move apples, apple trees or other host plants with soil, or nursery stock of apple,
crabapple or hawthorn, out of the Fraser Valley, Vancouver Island, or Prince George areas. Soil
under or adjacent to infested host trees may also contain apple maggot pupae, thus any plants
removed from the site with soil pose a risk of moving apple maggot.
*****************
So. . . What can we do with wormy fruit?
If your fruit has grubs, it is ruined as fresh fruit but you can still make juices, jams or jellies.
Trading fruit
Be careful. In the early stages, the damage may not be very noticeable from the outside.
Don’t sell or give away cherries if they are infested. That is how the fruit fly got here in the first
place, by someone unknowingly transporting infested fruit – and then probably throwing it out.
If you buy or are given cherries that turn out to have grubs (a) tell the grower and (b) don’t throw
them out but dispose of them properly as above.
Well, that is more than enough for this time, but it covers the CFF/rhagoletis and I
hope gives you a good picture of differences between dealing with CFF and SWD.
Best wishes,
Margaret


http://www.agf.gov.bc.ca/cropprot/tfipm/fruitfly.htm